“Once you’ve cloned a major gene in one crop, it is possible to find a counterpart gene that has the same function in another crop, and this is easier than finding useful genes from scratch” explains Leon Kochian, Professor in Plant Biology and Crop and Soil Sciences at Cornell University, USA, and Director of the Robert W Holley Center for Agriculture and Health, United States Department of Agriculture – Agricultural Research Service.
Aluminium toxicity and low phosphorus levels in acid soils are major factors that hinder cereal productivity worldwide, particularly in sub-Saharan Africa, South America and Southeast Asia. Globally, acid soils are outranked only by drought when it comes to stresses that threaten food security.
Tolerance to high levels of aluminium and low phosphorus is conferred by major genes, which lend themselves to cloning. Major genes are genes that by themselves have a significant and evident effect in producing a particular trait; it’s therefore easier to find and deploy a major gene associated with a desired trait than having to find and clone several minor genes.
Harvesting sorghum in Kenya.
Cloning major genes instrumental in hunt for resilient varieties
Locating a single gene within a plant’s DNA is like looking for a needle in a haystack. Instead of searching for a gene at random, geneticists need a plan for finding it.
The first step is to conduct prolonged phenotyping – that is, measuring and recording of plants’ observable characteristics in the field. By coupling and comparing this knowledge with genetic sequencing data, scientists can identify and locate quantitative trait loci (QTLs) – discrete genetic regions that contain genes associated with a desired trait, in this instance tolerance to aluminium or improved phosphorus uptake. They then dissect the QTL to single out the gene responsible for the desired trait. In the case of sorghum, researchers had identified the aluminium tolerance locus AltSB, and were looking for the gene responsible.
Once the gene has been identified, the next step is to clone it – that is, make copies of the stretch of DNA that makes up the gene. Geneticists need millions of copies of the same gene for their research: to gain information about the nucleotide sequence of the gene, create molecular markers to help identify the presence of the gene in plants and help compare versions of the gene from different species, and understand the mechanisms it controls and ways it interacts with other genes.
Drying the sorghum harvest in India.
Sorghum was one of the simpler crops to work with, according to Claudia Guimarães.
“Sorghum has a smaller genome… with clear observable traits, which are often controlled by one major gene,” she says.
The first breakthrough was the identification and cloning of SbMATE, the aluminium tolerance gene in sorghum behind the AltSB locus. The next was finding a diagnostic marker for the gene so that it could be used in breeding.
Marking genes to quickly scan plants for desired traits
Harvesting rice in The Philippines.
Once a desired gene is identified, a specific molecular marker must be found for it. This is a variation in the plant’s DNA, associated with a gene of interest, that scientists can use to flag up the gene’s presence. We can compare this process to using a text highlighter in a book, where the words represent the genes making up a genome. Each marker is like a coloured highlighter, marking sentences (genomic regions) containing particular keywords (genes) and making them easier to find.
In molecular breeding, scientists can use markers to quickly scan hundreds or thousands of DNA samples of breeding materials for a gene, or genes, that they want to incorporate into new plant varieties. This enables them to select parents for crosses more efficiently, and easily see which of the next generation have inherited the gene. This marker-assisted breeding method can save significant time and money in getting new varieties out into farmers’ fields.
Leon, who was also the Principal Investigator for various GCP-funded research projects, says that the cloning of SbMATE helped advance sorghum as a model for the further exploration of aluminium tolerance and the discovery of new molecular solutions for improving crop yields.
“This research also has environmental implications for badly needed increases in food production on marginal soils in developing countries,” says Leon. “For example, if we can increase food production on existing lands, it could limit agriculture’s encroachment into other areas.”
Rice field trials in Tanzania.
Aluminium toxicity is the result of aluminum becoming more available to plants when the soil pH is lower, and affects 38 percent of farmland in Southeast Asia, 31 percent in South America and 20 percent in East Asia, sub-Saharan Africa and North America. Meanwhile phosphorus, the second most important inorganic plant nutrient after nitrogen, becomes less available to plants in acid soils because it binds with aluminium and iron oxides. Almost half of the ricelands across the globe are currently phosphorus deficient. The research therefore has the potential for significant impact across the world.
The GCP-funded scientists used markers to search rice and maize for genes equivalent to sorghum’s SbMATE. In maize they successfully identified a similar gene, ZmMATE1, which is now being validated in Brazil, Kenya and Mali. In rice the search continues, but will become easier now that markers for ZmMATE1 have been developed.
Similarly, having validated, cloned and developed markers for PSTOL1 gene in rice, researchers at IRRI and JIRCAS then worked with researchers at EMBRAPA and Cornell University to use PSTOL1 markers to search for comparable genes in sorghum and maize. In both crops, genes similar to PSTOL1 have been identified and shown to improve grain yields under low-phosphorus soil conditions, albeit through different mechanisms.
The GCP-funded discoveries are already being used in marker-assisted selection in national breeding programmes in Brazil, Kenya, Niger, Indonesia, Japan, The Philippines and USA in sorghum, maize and rice. They have led to the release of new, aluminium-tolerant sorghum varieties in Brazil, with more currently being developed, along with phosphorus-efficient rice varieties.
Showing off freshly harvested sorghum in Kenya.
Cloning a worthwhile investment
Gene cloning was a relatively small cost in GCP’s research budget – about five percent (approximately USD 7 million) of a total research budget of USD 150 million spread over 10 years.
The gene-cloning component nonetheless yielded important genes for aluminium tolerance and phosphorus-uptake efficiency, within and across genomes. The molecular markers that have been developed are helping plant breeders across the world produce improved crop varieties.
Jean-Marcel Ribaut, Director of GCP, concludes: “The new markers developed for major genes in rice, sorghum and maize will have a significant impact on plant-breeding efficiency in developing countries.
“Breeders will be able to identify aluminium-tolerance and phosphorus-efficiency traits quicker, which, in time, will enable them to develop new varieties that will survive and thrive in the acid soils that make up more than half of the world’s arable soils.”
Humans are a protective species. We like to hoard away our precious items in vaults and safes made of concrete and steel, safe from thieves and catastrophes.
One not-so-obvious precious item, which many people take for granted, is seed. Without seeds, farmers would not be able to grow the grains, legumes, vegetables and fruits we eat.
For centuries, farmers have harvested seeds to store and protect for planting the following year. Most of the time, farmers will only keep seeds harvested from plants that have excelled in their environment – that have produced high yields or have favourable qualities such as larger or tastier grain. This simple iterative process of selecting primarily for high yields means that many crops today are closely related genetically, which can make them more vulnerable to evolving diseases and pests.
Without diversity, a severe epidemic can completely wipe out a farmer’s crop — and even a whole region’s crop. One of the best-known historical examples of just such a disastrous crop failure is the Irish Potato Famine of the 19th century, when potato blight disease caused extensive death, human suffering and social upheaval. A number of crops around the world are in similar danger today, including wheat, threatened by the Ug99 strain of stem rust disease, to which almost all the world’s wheat is susceptible, and cassava, menaced by African cassava mosaic virus (ACMV).
The solution – genetic diversity
Plant breeders are looking at ways to increase diversity among cultivated crops, mitigating the risks of pests and diseases and introducing genes that help plants thrive in their local environments. To do this they are looking for useful traits in traditional cultivars, related species and wild ancestors. Such traits may include tolerance to drought, heat, and poor soils as well as insect and disease resistance. Breeders cross these donor parents with high-yielding elite breeding lines. The resulting new varieties have all the preferred traits of their parents and none of the deficiencies.
The genetic diversity of crops and their wild relatives is held by gene banks. There are thousands of gene banks worldwide, which collect and store seeds from hundreds of thousands of varieties. Breeders and researchers submit seed and tissue of wild and cultivated varieties as well as of lines of new varieties they are trying to breed.
Staff hard at work in the medium-term storage room of the International Rice Genebank at IRRI.
“For years, gene banks were primarily repositories, but with genetics evolving, and its subsequent application in plant breeding growing over the past 10 years, breeders and geneticists are now mining gene banks for wild and exotic species that might have favourable genes for desired traits,” explains Ruaraidh Sackville Hamilton, evolutionary biologist and head of the International Rice Genebank maintained by the International Rice Research Institute (IRRI) at its headquarters in The Philippines.
Sifting through all these gene-bank collections for plants with desired traits is challenging for breeders, even for traits that are easy to select for through visual screening. For example, Ruaraidh says the rice collection held at the International Rice Genebank contains more than 117,000 different types of rice, or accessions.
In recognition of this challenge, the initial rationale of the CGIAR Generation Challenge Programme’s (GCP) genetic stocks activity was to make the diversity in gene banks more easily accessible and practical for the study – and application – of genetic diversity.
Taking stock of genetic stocks
The first step towards making diversity accessible to breeders was to develop reference sets, representing as much genetic diversity as possible within a small proportion of gene bank accessions, selected through pedigree and molecular marker information.
“A reference set represents the whole diversity found in the collections. Breeders can then use this sample to make crosses with their preferred varieties to try and integrate specific genes from the reference-set lines into those varieties.”
During the first phase of GCP (2004–2008), the Programme focused on identifying and characterising reference sets, each of roughly 300 lines, for banana, barley, cassava, chickpea, coconut, common bean, cowpea, faba bean, finger millet, foxtail millet, groundnut, lentil, maize, pearl millet, pigeonpea, potato, rice, sorghum, sweetpotato, wheat and yam. For most crops phenotyping data – information about physical plant traits – were also being made available for the reference sets, helping researchers to select material of interest for breeding.
A trainee at the International Maize and Wheat Improvement Center (CIMMYT) shows off diverse wheat ears, a small sample of the thousands of different lines found in the centre’s gene bank.
A further aspect of the work was the development of data-kits, which included molecular markers used to genotype and verify the sets. These kits allow plant scientists to assess and compare the diversity of their own collections with that of the reference sets, thus facilitating the introduction of new diversity in their prebreeding programmes.
Jean Christophe says the reference sets and data-kits were pivotal to the success of GCP’s molecular-breeding projects as they allowed researchers in different institutes to simultaneously work on the same genetic materials. “The sets served as consistent reference material that everybody collaborating on the project could analyse,” he explains. “Some of these collaborations involved hundreds of researchers, particularly those projects seeking to map genomes and identify genes.”
During the second phase of GCP (2009–2014), the reference sets for GCP’s Phase II target crops (cassava, chickpea, common bean, cowpea, groundnut, maize, rice, sorghum and wheat) were thoroughly phenotyped under different environments, including biotic and abiotic stresses. Jean Christophe says this work helped to identify new alleles (alternative forms of a gene or genetic locus) associated with desired traits that could be used for breeding purposes. Reference sets have been used successfully to identify and use new plant material in breeding programmes to improve various traits, particularly disease resistance and even more complex traits such as drought tolerance in cassava, chickpea, cowpea, maize, sorghum and wheat.
Broadening groundnut’s genetic base to prevent disease
A farmer in Senegal shows off her groundnut crop, almost ripe for harvest.
Another objective of GCP’s genetic stocks activity was to create new diversity within domesticated cultivated crops that have narrow genetic diversity, such as groundnut.
“The groundnuts we grow today are not too dissimilar to the ones that were first created naturally five to six thousand years ago,” says David Bertioli, a plant geneticist at the University of Brasília, Brazil. “This means that they are genetically very similar and have a narrow genetic base – the narrowest of any cultivated crop.”
This genetic similarity means that all cultivated groundnuts are very susceptible to diseases, particularly leaf spot, requiring expensive agrochemicals, especially fungicides. Without agrochemicals, which smallholder farmers in Africa and Asia often cannot afford, yields can be very low.
David says groundnut breeders always recognised the need to increase diversity, but because cultivated groundnuts have had a narrow base for so long, they became radically different from their wild relatives, making it very difficult to successfully cross wild species with cultivated species.
New genetic diversity is created through recombination, that is, through crossing contrasting varieties to create novel lines. Researchers can study these recombinants to identify genes associated with desired traits or use them in further crosses to develop new varieties.
“One of our first jobs was to make wild-species recombinants to trace out the relatedness of the wild-species genomes,” says David. “Once we could see the relatedness, we could see which wild species we could cross with cultivated lines. We had to do a lot of these crosses, but we eventually started to broaden the genetic diversity of the cultivated lines.”
David says this painstaking work, carried out under GCP, also formed the platform for sequencing the groundnut genome for the first time.
“That gave us an even greater understanding of the genetic structure, which is laying the groundwork for new varieties with traits such as added disease resistance and drought tolerance,” says David.
An additional key outcome of the groundnut aspect of the Legumes Research Initiative was developing ‘wild × domesticated’ synthetic lines, which are being crossed with domesticated groundnut varieties in Malawi, Niger, Senegal and Tanzania to introduce higher drought tolerance.
Like many areas of Africa struck by climate change, this village in Tanzania is suffering the effects of drought, with temperature increases and increasingly unpredictable rainfall.
Genetic gain by exploiting genetic stocks
The genetic stocks activity has generated a large and diverse array of resources across GCP’s target crops, not just for groundnut.
Recombinant inbred lines (RILs) incorporating specific traits of interest – particularly drought tolerance – have been developed for cowpea, maize, rice, sorghum and wheat. RILs are stabilised genetic stocks, created over several years by crossing two inbred lines followed by repeated generations of sibling mating to produce inbred lines that are genetically identical. These can then be used to discover and verify the role of particular genes and groups of genes associated with desired traits.
Near-isogenic lines (NILs) are RILs that possess identical genetic codes, except for differences at a few specific genetic loci. This enables researchers to evaluate particular genes and groups of genes that they may want to incorporate into breeding lines, particularly genes that have come from plants that otherwise do not perform well agronomically, such as wild relatives or older varieties. Sorghum NILs incorporating the AltSB locus for aluminium tolerance are being tested in Burkina Faso, Mali and Niger on problematic acid soils.
Multiparent advanced generation intercross (MAGIC) populations are a form of recombinants developed from crossing several parental lines from different genetic origins and, in some cases, exotic backgrounds to maximise the mix of genes from the parental lines in the offspring. MAGIC populations have been developed for chickpea, cowpea, rice and sorghum, and are being developed for common bean. Selected parental lines have been used to combine elite alleles for simple traits such as aluminium tolerance in sorghum and submergence tolerance in rice, as well as for complex traits such as drought or heat tolerance.
The further evaluation and use of the genetic stocks stemming from GCP-supported projects, as well as the generation of new genetic stocks, will continue beyond GCP through CGIAR’s Research Programs as well as through those institutes and national breeding programmes associated with GCP. There will be a continuing and evolving need to identify new genes associated with desired traits to improve cultivated germplasm.
Transplanting rice plants in Myanmar.
Sustaining genetic stocks into the future
Sustainability of genetic stocks has always been an issue, as stocks are generally not managed in a centralised way but are left under the direct responsibility of the scientists who developed them. These resources have therefore usually been handled in a highly ad hoc manner.
Because of high staff turnover in CGIAR Centers and breeding programmes in developing countries, and also because their management is neither centralised nor coordinated, these resources are also often lost as staff move from one organisation to another.
Although different genetic resources require different management protocols and storage timelines, the idea that gene bank curators take on the management of genetic stocks was proposed several years ago. For Centers such as IRRI, this is already a reality – for at least some of the genetic resources developed.
However, with the growing popularity of tapping into the rich diversity in gene banks that GCP’s genetic stocks activity has helped drive, gene bank supervisors such as Ruaraidh Sackville Hamilton are concerned about how genetic stocks will be sustained.
“The more popular molecular breeding and genetic stock become, the more funds we need to help us curate and disseminate them,” says Ruaraidh. He proposes to recover costs for managing genetic resources through a chargeback system on a two-tier scale, with non-profit organisations receiving stock at lower costs than commercial organisations. “Such a system would be sustainable and reduce the burden on gene bank institutes,” he says.
Still, the costs are of concern to institutes, particularly CGIAR Centers, which maintain most of the world’s plant crop gene banks.
CGIAR, a global partnership that unites 15 research Centres, including IRRI, is engaged in research for a food-secure future. CGIAR also created GCP. “CGIAR’s main priority is to conserve genetic resources for all humankind,” says Dave Hoisington, Senior Research Scientist and Program Director at the University of Georgia in the US. He was formerly Director of Research at the International Crops Research Institute for the Semi-Arid Tropics (ICRISAT) and Director of the Genetic Resources Program and of the Applied Biotechnology Center at the International Maize and Wheat Improvement Center (CIMMYT) (both CGIAR Centers) and Chair of the GCP Consortium Committee.
“In both of the CGIAR Centers I worked in,” says Dave, “we always maintained the position that if the Center were to shut down, the last thing we’d do would be to turn out the lights of the gene bank. Even when we had funding cuts, we would never cut the budget for the gene bank.”
At work in the maize active collection in the gene bank at CIMMYT, which keeps maize and wheat diversity in trust for the world.
New programme to fund crop diversity
To alleviate some of the funding burden on CGIAR Centers and free up more money to use in research and development, CGIAR created a new CGIAR Research Program for Managing and Sustaining Crop Collections. The comprehensive five-year programme is managed by the Crop Trust (formerly Global Crop Diversity Trust).
“The Trust is a financial mechanism to raise an endowment, to ensure the conservation and availability of crop diversity,” says Charlotte Lusty, Genebank Programmes Coordinator at the Global Crop Diversity Trust. “The new programme is an extension of the Trust’s work. We aim to raise a USD 500 million endowment by 2016. The interest from this will be divided between the CGIAR Centers to cover all their long-term conservation operations.”
The new programme is also reviewing how gene banks within CGIAR are being managed, with a view to developing a quality management system, which it hopes will make gene banks run more efficiently. Charlotte says it is also encouraging stronger gene banks, such as IRRI and CIMMYT, to lend their expertise and experience to smaller gene banks so they can meet and build on their management quality.
Dave Hoisington believes that the new programme will provide CGIAR’s gene banks with greater capacity and make them even more attractive for researchers wanting to make use of their rich diversity.
A wide diversity of rice seed from the collection of the International Rice Genebank at IRRI.
Looking forward 30 years
Tapping into new diversity was really at the heart of GCP, and was a major, if not the primary, rationale for its establishment. Over its 10-year lifespan, has invested almost USD 28 million, or 18 percent of its budget, in developing genetic stocks, both reference sets and recombinants, for over 20 different crops.
Although these products don’t directly benefit farmers, they do indirectly help by significantly increasing breeding efficiency.
“All this research is fairly new and I am amazed, as a geneticist and plant breeder, by how far we’ve come since GCP started in 2004,” says David Bertioli.
“What we’ve been able to do in groundnut – that is, broaden the genetic base – hasn’t occurred naturally or through conventional breeding for thousands of years. And we’ve been able to do it in less than ten years.”
David recognises that the true value of the research will only be realised when new disease-resistant varieties are available for farmers to grow, which may be in five to seven years. “Only then will we be able to look back and consider the worth of all the hard work and cooperation that went into developing these precious varieties.”
GCP’s genetic stock activities have generated a large and diverse array of resources. These resources lay the foundation for further genetic stock development and will aid in researchers’ quests to tap into genetic diversity well into the future.
Hei Leung has always been passionate about diversity, especially genetic diversity, and that’s one reason why he leapt at the chance to get involved with the CGIAR Generation Challenge Programme (GCP) right from its inception more than a decade ago.
But GCP’s attraction for Hei wasn’t just about genetic diversity; it was also about working with diverse institutes and researchers. At the time, Hei had been working for the International Rice Research Institute (IRRI) for some 10 years, on and off, including a stint at Washington State University in the USA.
“The whole idea of the Challenge Programme was to bring people together from different places instead of an individual CGIAR Centre doing things,” he says.
Hei also saw the likely spin-offs from rice research to other crops such as wheat, maize and sorghum, which are also crucial to food security.
“Rice is a ‘model crop’ because of its small genome. This means researchers in major cereals like wheat and maize, which have much bigger genomes but share genes of similar functions, can benefit from our work with rice.”
From little pizzas great programmes grow!
It all began in 2003, over pizza, in Rome. Hei remembers that his commitment to GCP started when he met with a small group of people including Robert Zeigler, who was to become the first Director of GCP, and who is currently Director General of IRRI.
“Little did we know that pizza was so inspiring,” Hei says, recalling that it was during that meeting that they agreed on the name: the Generation Challenge Programme.
GCP was formally launched in 2004 in Brisbane, Australia, at the 4th International Crop Science Congress.
Making the Programme ‘pro-poor’
Hei was initially involved with GCP as Subprogramme Leader for Comparative Genomics for Gene Discovery between 2004 and 2007, and later as a Principal Investigator for the Rice Research Initiative. Taking on his leadership role, Hei recognised from the start that many crops important to developing communities in Asia and Africa needed to become more drought-tolerant because of the increasing effects of climate change.
“We wanted to have a programme that is what we call ‘pro-poor’,” he says. “The majority of the world’s people depend on crops such as rice, wheat and maize for food.”
“I always feel that if you can solve eastern India’s problems, you can solve most of the problems in the world,” Hei adds. “If you travel in eastern India, you can see climate change happening day in, day out. You don’t have to wait 10 years or 50 years; it’s happening already. They either have too much or too little water. It’s a high-stress environment.”
Women at work threshing rice near Sangrur, Punjab, India.
Rice is the world’s most widely consumed cereal crop, and is particularly important as the staple food of 2.4 billion people in Asia. GCP recognised rice’s importance and invested almost USD 29.5 million in rice research and development.
Furthermore, the genetic breeding lessons learnt from rice can also be applied to other staple crops such as wheat, maize and sorghum.
They found sorghum and maize varieties that contained genes, similar to rice’s PSTOL1, that also conferred tolerance to phosphorus-deficient soils by enhancing the plant’s root system. They were then able to develop molecular markers to help breeders in Brazil and Africa to identify lines with these genes, which can now be used in breeding and developed as varieties for farmers growing crops, particularly in acidic soils.
Seeing the potential for novel researcher interactions
Hei also recognised that crops that received less scientific attention but remained important as regional staple foods, such as bananas and plantains (of the genus Musa), could benefit from comparative genomics research.
“We had a highly motivated group of researchers willing to devote their efforts to Musa,” remembers Hei, who is currently IRRI Program Leader of Genetic Diversity and Gene Discovery.
“GCP’s community could offer a framework for novel interactions among banana-related actors and players working on other crops, such as rice. So, living up to its name as a Challenge Programme, GCP decided to take the gamble on banana genomics and help it fly.”
A banana farmer at work in the Philippines.
However, after four years, Hei found it difficult to maintain his GCP leadership role as well as keep on top of his IRRI work: “They said I was 50 percent with IRRI and 50 percent with GCP, but it is never like that in reality. I was always doing two jobs, or at least one-and-a-half jobs, and I didn’t think I was doing a good enough job for either. I thought it was time for other people to come into GCP.”
While Hei stepped down from a leadership role, he remained active working on GCP projects throughout the life of the Programme.
Hei says that during the last five years of GCP, a lot of technology to characterise genetic diversity evolved “to bring high-quality science to accelerate our mission to help the poor areas of Asia and Africa.”
A MAGIC affair
The development of MAGIC (multi-parent advanced generation intercross) populations is the project that Hei gets most excited about. From these populations, created by crossing different combinations of multiple parents, plant lines can be selected that have useful characteristics such as drought tolerance, salinity tolerance and the ability to produce better quality grain.
“Now many crop breeders are calling for MAGIC populations,” says Hei. “I feel proud that at GCP we decided to support this concept and activity. This is one of GCP’s most important legacies and it’s one of my most favourite things.”
Hei Leung looking relaxed in the lab at IRRI.
Honoured as a Fellow of the American Phytopathological Society (APS), Hei is recognised “for his leadership in the international community toward building and distributing rice genetic and genomic resources and creating capacity in plant pathology in the developing countries of Asia.”
Hei’s GCP leadership and research have clearly provided him with an important platform for taking on leadership and champion roles linking many individuals and organisations across Asia and Africa. His ASP profile concludes: “His promotion of collaborative research and his leadership in such programmes in the developing world have contributed to the building of a dynamic research community that promotes both basic knowledge and food security for Asia and the world.”
Making a difference to food security and farmer’s lives in developing countries is what GCP is all about. Such differences have been made possible through collaborative links that connect a diversity of organisations and people with the latest research in genetic diversity and breeding techniques.
A farmer transplants rice in the Philippines.
It’s amore!
Hei recalls his personal and professional journey with GCP with much affection: “I think that it has been a wonderful scientific journey in terms of knowing the science and opening up my mind to being more receptive to alternative ways of doing things.
“There have been so many friends I have met through networking with GCP. Sometimes you go through bumpy roads, but anything you do will have bumpy times. And it’s very unusual to have a programme so illuminating. We honoured our commitment to finish in 10 years. It is a programme that had a fresh start and a clean ending.
“Most importantly, GCP has enabled plant breeders to embrace cutting-edge science through partnerships that focused on improving crop yields in areas previously deemed unproductive,” he says. “GCP is unique, one-of-a-kind, and I love it!”
“What we have done within the Generation Challenge Programme,” explains Jurandir Magalhães, now a senior scientist for EMBRAPA, as he reflects back on the past decade, “is speed up maize and sorghum breeding for acidic soil adaptation”.
Almost 70 percent of Brazil’s arable land is made up of acidic soils. That means the soil has toxic levels of aluminium and low levels of phosphorous – a lethal combination that makes crop production unsustainable. Aluminium toxicity in soil comes close to rivalling drought as a food-security threat in critical tropical food-producing regions. This is because acidic soils reduce root growth and deprive plants of the nutrients and water they need to grow.
Robert Schaffert – EMBRAPA’s longest-serving sorghum breeder – had developed mapping populations for aluminium tolerance in sorghum; these populations were the basis for the work supported by GCP.
During the first four years of the 10-year Programme, Jurandir was able to identify and clone the major aluminium-tolerance gene in sorghum – AltSB – using these mapping populations. The cloned gene has since enabled researchers across Africa and Asia to quickly and efficiently breed improved sorghum and maize plants that can withstand acidic soils.
Jurandir, speaking today about the work to advance sorghum genetic resources, says: “Wherever there are acidic soils with aluminium toxicity and low phosphorous availability, our results should be applicable.”
His story with EMBRAPA is one of many where GCP-supported projects have been instrumental in helping global research centres achieve their goals, which ultimately will help farmers worldwide.
“One important focus of GCP was linking basic research to applied crop breeding,” Jurandir says. “This is also the general orientation of our programme at EMBRAPA. We develop projects and research to produce, adapt and diffuse knowledge and technologies in maize and sorghum production by the efficient and rational use of natural resources.
“GCP provided both financial support and a rich scientific community that were useful to help us attain our common objectives.”
EMBRAPA’s work on cloning the AltSB gene would prove to be one of the first steps in GCP’s foundation sorghum and maize projects, both of which sought to provide farmers in the developing world with crops that will not only survive but thrive in the acidic soils where aluminium toxicity reduces crop production.
Leon Kochian of Cornell University in the US was Jurandir’s supervisor at the time when they applied for GCP funding. Leon was a Principal Investigator for various GCP research projects, researching how to improve grain yields of crops grown in acidic soils.
“The breeders are so important,” says Leon about the importance of supporting institutes such as EMBRAPA to advance plant genetics. “Ultimately, they are the cliché of ‘the rubber hits the road’. They’re the ones who translate what we’re trying to figure out into the actual crop improvements. That’s really what it’s all about.”
“That’s why EMBRAPA is a unique institution. Their mission is to get improved seed out, new germplasm out, for the farmers. They have the researchers in sorghum and maize breeding [Robert Schaffert and Sidney Parentoni] and molecular biology [Jurandir Magalhães and Claudia Guimarães].”
Maize farmers in Brazil.
Great minds think alike
Jurandir’s EMBRAPA colleague Claudia Guimarães, a plant molecular geneticist focusing on maize, says GCP promoted ‘products’, which also echoed the mission statement of EMBRAPA’s Maize & Sorghum research centre.
The centre’s mission is to: ‘Generate, adapt and transfer knowledge and technology that allows for the efficient production and use of maize, sorghum, and natural resources as well as promotes competitiveness in the agriculture sector, sustainable development, and the well-being of society.’
GCP, says Claudia, “wanted to extract something else from the science – products – the idea of a real, touchable product. You have to have progress: germplasm, lines, markers; they are quite practical things.
“The major goal of GCP is to deliver products that can improve people’s lives worldwide. So it needs to be readily available and useful for other scientists and for the whole community.”
GCP wanted to ensure that research products could and would be adopted, adapted and applied for the ultimate benefit of resource-poor farmers. The Programme therefore set out to catalyse interactions between the various players who are needed to bridge the gap between strategic research in advanced labs and resource-poor farmers.
GCP and EMBRAPA were both working towards tangible applied outcomes, says Claudia: “GCP was not only giving you money, they are really serious about what are you doing: ‘Did you deliver everything you promised?’”
Claudia delivered. She and her team at EMBRAPA were able to find an important aluminium-tolerance gene in maize similar to the sorghum gene. This outcome provided the basic materials for molecular-breeding programmes focusing on improving maize production and stability on acidic soils in Africa and other developing regions.
Maize trials in the field at EMBRAPA. The maize plants on the left are aluminium-tolerant while those on the right are not.
Multifaceted and tangible results
Through further GCP funding, EMBRAPA researchers Robert Schaffert and Sidney Parentoni were able to work together with two researchers from Kenya, Dickson Ligeyo and Samuel Gudu, to develop a breeding programme to combine the improved Brazilian germplasm with locally adapted Kenyan materials. A new base of improved germplasm was established for Kenyan breeders, which allowed the development of varieties adapted to acidic soils in Kenya.
Sidney, a maize breeder for GCP projects and now the deputy head of research and development for EMBRAPA Maize & Sorghum, says that the benefits of being part of GCP are multifaceted: “It was very important, not only for EMBRAPA as an institute, but also individually for each of the participants that had the opportunity to interact with partners in different parts of the word,” says Sidney.
A Kenyan farmer with her sorghum crop.
“Each of them adds a piece to build the results achieved by GCP, which from my perspective promoted a number of advances in the areas of genetics and breeding.
“Technologies such as root image scanning developed at Cornell [University] were transferred to EMBRAPA and allowed us to do large-scale screening in a number of maize and sorghum genotypes with large impacts in phosphorous-efficiency studies.
“Scientists from Africa were trained in breeding and screening techniques at EMBRAPA, and Brazilian scientists had the opportunity to go to Africa and interact with African researchers to jointly develop strategies for breeding maize and sorghum for low-phosphorous and acidic soils.
“These trainings and exchanges of experiences were very important for the people and for the institutions involved,” says Sidney.
Sustainable partnerships to break ground for groundnut
Groundnut
Soraya Leal-Bertioli is a researcher in the EMBRAPA Genetic Resources & Biotechnology centre. She works on groundnut (also known as peanut), and formed part of the GCP team working on groundnut with tolerance to drought and resistance to diseases and fungal contamination. She concurs that GCP united researchers from all over the globe in a common goal.
“GCP not only identified groups, but it went out, searched for people and invited contributions, offered resources to get them together. GCP brought partnerships to a whole new level,” Soraya says.
“Last time I checked there were 200 partners in 50 countries. No one is able to do that. It required a lot of money, a lot of resources, but the way it was dealt with in GCP was: ‘Let’s reach out for the main players, the ones who have the technology, and also the ones who can use the technology’.
“GCP used the resources for the benefit of the community and brought everybody together.”
Soraya says the traditional way of funding research often had ‘no structure’.
“Sometimes a university or funding body receives a large amount of money and decides to build something, a new institute in the middle of the jungle somewhere, but they don’t have anybody to run it; it is not sustainable.
“What GCP did was help to provide the structure and the agents for the whole system. They helped train the people to run the whole system. This is a very sustainable model, which is very likely to give good results in a much shorter time frame than other programmes.”
Watch Soraya – and other members of the team – discuss the complex personality of groundnut and groundnut research in our video series:
Genetic stocks AND people are products
The products and outcomes of the collaboration with GCP have included both the tangible and the not-so-tangible. Sidney says that a large quantity of Brazilian improved maize and sorghum lines tolerant to acidic soils has been developed over the years at EMBRAPA.
“These materials were shared with partners in Africa, and this was a major contribution to Kenyan farmers, as part of this collaborative work done in the scope of GCP.
“To be part of the programme has been very important for EMBRAPA’s research team. It has given us the opportunity to interact with a diversity of institutes.”
Sidney concludes: “In this large network of partnerships, EMBRAPA was able to learn and to share information in a highly productive way.
“From my perspective, the involvement with GCP projects allowed me to grow as a researcher and as a person, and also at the same time to share and to acquire new knowledge in a number of areas. I think it was a ‘win-win’ interaction for all the participants.”
Many of the products generated within the scope of GCP, such as markers and germplasm, are already available within EMBRAPA’s breeding programmes. Avenues for further research have been paved based on the GCP achievements, and these new research lines will be continued within new projects.
As Claudia says: “The strong partnerships built along the way with GCP will be maintained by us joining with new research teams from other institutes and countries to work on new projects.”
Plant geneticist Sigrid Heuer remembers very clearly entering the transgenic greenhouse in Manila to see her postdoctoral student holding up a rice plant with ‘monster’ roots.
“They were enormous,” she recalls. “This is when I knew we had the right gene. It confirmed years of work. That was our eureka moment.
So massive was the effect of that gene that I knew we had the right one.”
This genetic discovery – described in more detail a little later – is one of the shining lights of the 10-year-long CGIAR Generation Challenge Programme (GCP) established in 2004.
GCP-supported researchers aimed high: they wanted to contribute to food security in the developing world by using the latest advances in crop science and plant breeding.
And with the lives of half of the world’s population directly reliant on their own agriculture, there is a lot at stake. Land degradation, salinity, pollution and excessive fertiliser use are just some of the challenges.
Rice is one of the most critical crops worldwide
Amelia Henry, drought physiology group leader at the International Rice Research Institute (IRRI), explains why rice was such a critical crop for GCP research. She says rice is grown in a diverse set of environmental settings, often characterised by severe flooding, poor soils and disease.
Cycling through rice fields in Odisha, India.
In Asia, 40 percent of rice is produced in rainfed systems with little or no water control or protection from floods and droughts – meaning rice plants are usually faced with too much or too little water, and rarely get just enough. In addition, 60 percent (29 million hectares) of the rainfed lowland rice is produced on poor and problem soils, including those that are naturally low in phosphorus.
Phosphorus deficiency and aluminium toxicity are two of the most widespread environmental causes of poor crop productivity in acidic soils, where high acid levels upset the balance of available nutrients. And drought makes these problems even worse.
Phosphorus is essential for growing crops. Its commercial use in fertilisers is due to the need to replace the phosphorus that plants have extracted from the soil as they grow. Soils lacking phosphorus are an especially big problem in Africa, and the continent is a major user of phosphate fertilisers. However, inappropriate use of fertilisers can, ironically, acidify soil further, since excess nitrogen fertiliser decreases soil pH.
Meanwhile, high levels of aluminium in soil cause damage to roots and impair crop growth, reducing their uptake both of nutrients like phosphorus and of water – making plants more vulnerable to drought. Aluminium toxicity is a major limitation on crop production for more than 30 percent of farmland in Southeast Asia and South America and approximately 20 percent in East Asia, sub-Saharan Africa and North America.
The challenge today is to tap into the genetic codes of key crops such as rice and wheat to feed a growing global population. Science plays a crucial role in identifying genes for traits that help plants tolerate more difficult environmental conditions, and producing crop varieties that contain these genes.
Plant biologists are already developing new rice lines that produce higher yields in the face of reduced water, increasingly scant fertiliser as costs rise, and unproductive soils. However, ‘super’ crops are needed that can combine these qualities and withstand climate changes such as increasing temperatures and reduced rainfall in a century when the world’s population is estimated to reach nearly 10 billion people by 2050.
Bringing the best scientific minds to improve rice varieties
Ambitious in concept, the GCP research focussed on bringing together experts to work on these critical problems of rice production for some of the world’s poorest farmers.
The programme was rolled out in two phases that sought to explore the genetic diversity of key crops and use the most important genes for valuable traits, such as Sigrid’s discovery made in a rice variety that is tolerant of phosphorus-poor soils. Each phase involved dedicated teams in partner countries.
GCP Principal Investigator Hei Leung, from IRRI, says GCP is unique, one of kind: “I love it.” He says GCP has enabled rice researchers and breeders to embrace cutting-edge science through partnerships focussed on improving crop yields in areas previously deemed unproductive.
Hei says GCP wanted to target research during its second phase on those crops that most poor people depend upon. “We wanted to have a programme that is what we call ‘pro-poor’, meaning the majority of the world’s people depends on those crops,” he says.
Rice is the ‘chosen one’ of GCP’s cereal crop research and development, with the biggest slice of GCP’s research activities dedicated to this, the most widely consumed staple food.
It is crucial to increase rice supplies by applying research and development such as that carried out by GCP researchers over the past 10 years, Hei says.
Relying on rice’s small genome in the hunt for drought-tolerance genes
Researchers had been trying to map the genomes of key cereal crops for over two decades. Rice’s genome was mapped in 2004, just as GCP started.
Rice has a relatively small genome, one-sixth the size of the maize genome and 40 times smaller than the wheat genome. This makes it a useful ‘model’ crop for researchers to compare with other crops.
“People like to compare with rice because wheat and maize have very big genomes, and they don’t have the resources,” explains Hei.
After the rice genome had been sequenced, the next step was to focus down to a more detailed level: the individual genes that give rice plants traits such as drought tolerance. Identifying useful genes, and markers that act as genetic ‘tags’ to point them out, gives scientists an efficient way to choose which plants to use in breeding.
One of GCP’s Principal Investigators for rice was Marie-Noëlle Ndjiondjop, a senior molecular scientist with the Africa Rice Center.
“Rice is becoming a very important crop in Africa,” she says. “Production has been reduced by a lot of constraints, and drought is one of the most important constraints that we face in Africa.”
Meet Marie-Noëlle below (or on YouTube), in our series of Q&A videos on rice research in Africa.
Marie-Noëlle’s team recognised that drought tolerance was likely to be a complex trait in rice, involving many genes, due to the mix of physiological, genetic and environmental components that affect how well a plant can tolerate drought conditions. To help discover the rice varieties likely to have improved drought tolerance, Marie-Noëlle’s team used an innovative approach known as bi-parental marker-assisted recurrent selection (MARS).
“With such a complex trait, you really need to have all the tools and infrastructure necessary; through GCP we were able to buy the necessary equipment and put in the infrastructure needed to find and test the drought trait in rice lines.
“By using the MARS approach we identified the genetic regions associated with drought and are moving towards developing new rice lines that the African breeder and farmer will be using in the next decade to grow crops that are better able to withstand drought conditions.”
Likewise, Amelia Henry’s IRRI team also developed drought-tolerant lines, particularly for drought-prone areas of South Asia. She says many of the promising deep-rooted or generally drought-tolerant varieties identified in the early decades after IRRI’s foundation in 1960 are still used today as ‘drought donors’.
“Since the strength of our project was the compilation of results from many different sites, this work couldn’t have been done without the GCP partners,” she says. “They taught me a lot about how rice grows in different countries and what problems rice farmers face.”
Hei agrees that GCP partnerships have been crucial, including in the successful breeding of rice with drought tolerance: “They’re getting a 1.5-tonne rice yield advantage under water stress. I mean, that’s unheard of! This is a crop that needs water.”
A rice farmer in Rwanda.
But the researchers could not rest with just one of rice’s problems solved.
Hei says GCP’s initial focus on drought was a good one but then, “I remember saying, ‘We cannot just go for drought. Rice, like all crops, needs packages of traits’.”
He knows that drought is just one problem facing rice farmers, noting “this broadened our research portfolio to include seeking to breed rice varieties with traits of tolerance to aluminium toxicity, salt and poor soils.”
The scope widens: phosphorus-hungry rice and a huge success
Sigrid Heuer was in The Philippines working for IRRI when she became involved in the ground-breaking phosphorus-uptake project for rice.
She took over the project being headed by Matthias Wissuwa. Much earlier, Matthias had noted that Kasalath – a traditional northern Indian rice variety that grew successfully in low-phosphorus soil – must contain advantageous genes. His postdoctoral supervisor, Noriharu Ae, thought that longer roots were likely to be the secret to some rice varieties being able to tolerate phosphorus-deficient soils.
Matthias, now a senior scientist in the Crop, Livestock and Environment Division at the Japan International Research Center for Agricultural Sciences (JIRCAS), says that for a long time he was not sure if it was just long roots: “It was a real chicken-and-egg scenario – does strong phosphorus uptake spur root growth, or is it the other way around?”
Screening for phosphorus-efficient rice, able to make the best of low levels of available phosphorus, on an IRRI experimental plot in The Philippines. Some types of rice have visibly done much better than others.
Sigrid Heuer used her background in molecular breeding to take up the challenge with GCP to find the genes responsible for the Kasalath variety’s long roots.
“I spent years looking for the gene,” Sigrid says. “It was like trying to find a needle in a haystack; the genomic region where the gene is located is very complex.
“We had little biogenomics support at the time and I had three jobs and two kids; I was spending all my nights trying to find this gene.”
Sigrid Heuer in the field at IRRI.
But one day, Sigrid’s postdoctoral student Rico Gamuyao excitedly called her downstairs to the transgenic greenhouses. “Rico had used transgenic plants to see whether this gene had any effect. He was digging out plants from experimental pods.”
Sigrid says that moment in the Manila labs was the turning point for the project’s researchers.
Matthias’ team had previously identified a genomic region, or locus, named Pup1 (‘phosphorus uptake 1’) that was linked to phosphorus uptake in lines of traditional rice growing in poor soils. However, its functional mechanism remained elusive until the breakthrough GCP-funded project sequenced the locus, showing the presence of a Pup1-specific protein kinase gene, which was named PSTOL1 (‘phosphorus starvation tolerance 1’). The discovery was reported in the prestigious scientific journal Nature on 23 August 2012 and picked up by media around the world.
The gene instructs the plant to grow larger and longer roots, increasing its surface area – which Sigrid compares to having a bigger sponge to absorb more water and nutrients in the soil.
“Plants growing longer roots have more uptake of phosphorus – and PSTOL1 is responsible for this.
“GCP was always there, supporting us and giving us confidence, even when we weren’t sure we were going to succeed,” she recalls. “They really wanted us to succeed, so, financially and from a motivational point of view, this gave us more enthusiasm.”
She adds, jokingly, “With so many people having expectations about the project, it was better not to disappoint.”
For some insight straight from the source, listen to Matthias in our podcosts below. In these two bitesized chunks of wisdom he discusses the importance of phosphorus deficiency and of incorporating PSTOL1 into national breeding programmes; his work in Africa and the possibility of uncovering an African ‘Pup2’; what the PSTOL1 discovery has meant for him; and the essential contribution of international partnerships and GCP’s support.
Members of the IRRI PSTOL1, phosphorus uptake research team chat in the field in 2012. From left to right they are are: Sigrid Heuer, Cheryl Dalid, Rico Gamuyao, Matthias Wissuwa and Joong Hyoun Chin.
Phosphorus-uptake gene not all it seemed – an imposter?
But PSTOL1 was definitely not what it seemed. “It was identified under phosphorus-deficient conditions and the original screen was set up for that,” says Sigrid.
Researchers eventually discovered that Pup1 and the PSTOL1 gene within it were not really all about phosphorus at all: “It turns out it is actually a root-growth gene, which just happens to enhance uptake of phosphorus and other nutrients such as nitrogen and potassium.
“The result is big root growth and maintenance of that growth under stress. If you have improved root growth, there is more access to soil resources, as a plant can explore more soil area with more root fingers.”
Her team showed that overexpression of PSTOL1 gene significantly improves grain yield in varieties growing in phosphorus-deficient soil – by up to 60 percent compared to rice varieties that did not have the gene.
In field tests in Indonesia and The Philippines, rice with the PSTOL1 gene produced about 20 percent more grain than rice without the gene. This is important in countries where rice is grown in poor soils.
A farmer harvests rice in South Sulawesi, Indonesia.
Sigrid, now based in Adelaide at the Australian Centre for Plant Functional Genomics, says the introduction of the new gene into locally adapted rice varieties in different locations across Asia and Africa is expected to boost productivity under low-phosphorus conditions.
“The ultimate measure for these kinds of projects is whether a gene works in different environments. I think we have a lot of evidence that says it does,” she says.
The discovery of PSTOL1 promises to improve the food security of rice farmers on phosphorus-deficient land though assisting them to grow more rice and earn more.
Titbits of further research successes: aluminium tolerance and MAGIC genes
Drought, low-phosphorus soils, aluminium toxicity, diseases, acid soils, climate change… the list seems never-ending for challenges to growing rice. Apart from the successes with drought and phosphorus that GCP scientists achieved, there was to be much more in the works from other GCP researchers.
In Phase II, they worked towards breeding aluminium-tolerant sorghum lines for sub-Saharan Africa, as well as applying what they learnt to discover similar genes in rice and maize.
Hei Leung says GCP leaves a lasting legacy in the development of multiparent advanced generation intercross (MAGIC) populations. These help breeders to identify valuable genes, and from among the populations they can also select lines to use in breeding that have favourable traits, such as being tolerant to environmental stresses, having an ability to grow well in poor soils or being able to produce better quality grain.
“MAGIC populations will leave behind a very good resource towards improving different crop species,” says Hei. “I’m sure that they will expand on their own.”
GCP funded the development of four different MAGIC populations for rice, including both indica and japonica types. And the idea of developing MAGIC populations has spread to other crops, including chickpeas, cowpeas and sorghum.
Meeting the challenges and delivering outcomes to farmers
But with success come the frustrations of getting there, according to Nourollah Ahmadi, GCP Product Delivery Coordinator for rice across Africa. “This is because things are not always going as well as you want.”
Project Delivery Coordinators monitor projects first-hand, conducting on-site visits, advising project leaders and partners and helping them implement delivery plans.
“One of the problems was the overall level of basic education of people who were involved in the project,” Nourollah says.
Rice cultivation in Mali is on the rise.
His work with GCP has opened up new prospects for some of the poorest farmers in the world: “For five years, I have been coordinating one of the rice initiatives implemented by the Africa Rice Center and involving three African countries.” These are Burkina Faso, Mali and Nigeria.
He says GCP has brought much-needed expertise and technical skills to countries which can now use genetic insights to produce improved crops tolerant of drought conditions and poor soils and resistant to diseases. Using new molecular-breeding techniques has provided a more effective way to move forward, still firmly focussed on helping the world’s poorest farmers achieve food security.
“We don’t change direction, we change tools – sometimes you have a bicycle, sometimes you have a car,” Nourollah says.
Hei agrees there have been challenges: “It’s been a bumpy road to get to this point. But the whole concept of getting all the national partners doing genetic resource characterisation is a very good one.
Right now they are enabled; they are not scared about the technology. They can apply it.”
Sigrid says applied research is judged on two scales: “One is the publications and science you’re doing. The other is whether the work has any impact in the field, whether it works in the field. Bringing these two together is sometimes a challenge.”
GCP has managed to meet both challenges. New crop varieties have been released to farmers, and more than 450 scientifically reviewed papers have been published since 2004.
Building on the rice success story and leaving a lasting legacy
The work that GCP-supported researchers have done for rice is also being used in other crops. For example, researchers used comparative genomics to determine if genes the same as or similar to those found in rice are present and operating in the same manner in sorghum and maize.
The GCP team found sorghum and maize varieties that contained genes, similar to rice’s PSTOL1, that also confer tolerance of phosphorus-deficient soil with an enhanced root system. They were then able to develop markers to help breeders in Brazil and Africa identify phosphorus-efficient lines.
The knowledge that GCP-supported rice researchers have generated is shared through communities of practice, through websites, publications, research meetings and the Integrated Breeding Platform.
As Amelia Henry notes, GCP’s achievements will be defined by “the spirit of dedication to openness with research data, results and germplasm and giving credit and support to partners in developing countries.” The work in rice in many ways exemplifies GCP’s collaborative approach, commitment to capacity building and deeply held belief that together we can go so much further in helping farmers.
Unlocking genetic diversity in crops for the resource-poor was at the heart of GCP’s mission, which in 2003 promised ‘a new, unique public platform for accessing and developing new genetic resources using new molecular technologies and traditional means’.
Certainly for poor rice farmers in Asia and Africa, the work that GCP has supported in applying the latest molecular-breeding techniques will lead to rice varieties that will help them produce better crops on poor soils in a changing climate.
And get an extra Sunset helping of rice in our tale of GCP’s relationship with IRRI, with more on MAGIC populations and breeding for salinity tolerance
It’s a cruel feature of some of the most populous areas of the world, particularly in the tropics and subtropics: acid soils. They cover a third of the world’s total land area – including significant swathes of Africa, Asia and Latin America – and 60 percent of land we could use for growing food. Today around 30 percent of all arable land reaches levels of acidity that are toxic to crops.
Soil acidity occurs naturally in higher rainfall areas and varies according to the landscape and soil. But we also make the problem worse through intensive agricultural practices. The main cause of soil acidification is the overuse of nitrogen fertilisers, which farmers apply to crops to increase production. Ironically, the inefficient use of nitrogen fertiliser can instead make matters worse by decreasing the soil pH.
60 percent of the world’s potential crop-growing land is highly acidic. Map courtesy of Leon Kochian.
Acidity prevents crops from accessing the right balance of nutrients in the soil, limiting farmers’ yields. Its negative effect on world yield is second only to drought and is particularly hard felt by subsistent and smallholder farmers who cannot afford to correct soil pH using calcium-rich lime. As a result, these farmers are forced to grow less profitable, acid-tolerant crops like millet, or suffer huge yield losses when growing more popular cereal crops like wheat, rice or maize.
“In Kenya, acidic soils cover almost 90 percent of the maize-growing areas and can reduce yields by almost 60 percent,” says Samuel Gudu, Professor and Deputy Vice-Chancellor (Planning & Development) at Moi University in Kenya. “Farmers know that the soil affects their yields, but they still grow maize because it is so popular.”
As is true in many other sub-Saharan countries, maize is a staple of the Kenyan diet: the average Kenyan consumes 98 kilograms of it each year. But maize prices in Kenya are among the highest in Africa, which directly affects the poorest quarter of the population, who spend 28 percent of their income on the crop.
“Yield losses play a big part in this economic imbalance and are why we need affordable agronomic options to help our farmers improve yields,” says Samuel, who was a Principal Investigator of a GCP comparative genomics project which sought to provide some of these options.
A Kenyan farmer prepares her maize plot for planting. Acid soils cover almost 90 percent of Kenya’s maize-growing area, and can more than halve yields.
Aluminium toxicity and phosphorus deficiency: Public enemies number one and two in the fight against acidic soils
Between 2004 and 2014, crop researchers and plant breeders across five continents collaborated on several GCP projects to develop local varieties of maize, rice and sorghum that can withstand phosphorus deficiency and aluminium toxicity – two of the most widespread constraints leading to poor crop productivity in acidic soils.
Aluminium toxicity is the primary limitation on crop production for more than 30 percent of farmland in Southeast Asia and Latin America and approximately 20 percent in East Asia, sub-Saharan Africa and North America. Aluminium becomes more soluble in acid souls, creating a toxic glut of aluminium ions that damage roots and impair their growth and function. This results in reduced nutrient and water uptake, which in turn depresses yield.
Phosphorus deficiency is the next biggest soil deficiency after nitrogen to limit plant production. In acid soils, phosphorus is stuck (fixed) in forms that plants cannot take up. All plants need phosphorus to survive and thrive; it is a key element in plant metabolism, root growth, maturity and yield. Plants deficient in phosphorus are often stunted.
In a double whammy, the damage that aluminium toxicity causes to roots means that plants cannot efficiently access native soil phosphorus or even added phosphorus fertiliser – and adding phosphorus is an option that is rapidly becoming less viable.
“The world is running out of phosphorus as quickly as it is running out of oil,” says Leon Kochian, a Professor in the Departments of Plant Biology and Crop and Soil Science at Cornell University in the USA. “This is making its application a more expensive and less sustainable option for all farmers wanting to improve yields on acidic soils.” Indeed, the price of rock phosphate has more than doubled since 2007.
For 30 years, Leon has combined lecturing and supervising duties at Cornell University and the United States Department of Agriculture with his scientific quest to understand the genetic and physiological mechanisms that allow some cereals to tolerate acidic soils while others wither. And for the last 10 years, he has played an important leading role in GCP’s effort to develop new, higher yielding varieties of maize, rice and sorghum that tolerate acidic soils.
GCP builds on past crop breeding successes
The rationale behind GCP’s efforts stems from two independent and concurrent projects, which had been flourishing on different sides of the Pacific well before GCP was created.
One of those projects was co-led by Leon at Cornell University in collaboration with a previous PhD student of his, Jurandir Magalhães, at the Brazilian Corporation of Agricultural Research (EMBRAPA) Maize & Sorghum research centre.
Working on the understanding that the cells in grasses like barley and wheat use ‘membrane transporters’ to insulate themselves against excessive subsoil aluminium, Leon and Jurandir searched for a similar transporter in the cells of sorghum varieties that were known to tolerate aluminium.
“In wheat, when aluminium levels are high, these membrane transporters prompt organic acid release from the tip of the root,” explains Jurandir. “The organic acid binds with the aluminium ion, preventing it from entering the root.” Jurandir’s team found that in certain sorghum varieties, the gene SbMATE encodes a specialised organic acid transport protein, which stimulates the release of citric acid. They cloned the gene and found it was very active in aluminium-tolerant sorghum varieties. They also discovered that the activity of SbMATE increases the longer the plant is exposed to high levels of aluminium.
The rice variety on the left (IR-74) has the the gene locus Pup1, conferring phosphorus-efficient longer roots, while that on the right does not.
The other project, co-led by Matthias Wissuwa at Japan International Research Centre for Agricultural Sciences (JIRCAS) and Sigrid Heur at the International Rice Research Institute (IRRI) in The Philippines, was looking for genes that could improve rice yields in phosphorus-deficient soils. They had already identified a gene locus (a section of the genome containing a collection of genes) that produced a protein which allowed rice varieties with to grow successfully in low-phosphorous conditions. The locus was termed ‘phosphorus uptake 1’ or Pup1 for short. With GCP support, the team were able to make the breakthrough of discovering the protein kinase gene responsible, PSTOL1 (‘phosphorus starvation tolerance 1’), and understanding its mechanism.
“In phosphorus-poor soils, this protein instructs the plant to grow larger, longer roots, which are able to forage through more soil to absorb and store more nutrients,” explains Sigrid, a plant geneticist at IRRI and a GCP Principal Investigator. “By having a larger root surface area, plants can explore a greater area in the soil and find more phosphorus than usual. It’s like having a larger sponge to absorb more water.”
Screening for phosphorus-efficient rice, able to make the best of low levels of available phosphorus, on an International Rice Research Institute (IRRI) experimental plot in the Philippines. Some types of rice have visibly done much better than others.
Leon clarifies that both projects were fairly advanced before they became part of the GCP fold. “Our team had already identified the gene SbMATE and were in the process of cloning it for breeding purposes. The IRRI and JIRCAS team had also identified Pup1 and were in the process of identifying and cloning the gene.”
The purpose of cloning these genes was to create molecular markers to help breeders identify whether the genes were present in the varieties they were working with. As an analogy, think of ‘reading’ a plant’s genome as you would read a story: the story’s words are the plant’s genes, and a molecular marker works as a text highlighter. Different markers can highlight or tag different keywords in the story. Tagging the location of beneficial genes in the DNA of plant genomes allows scientists to see which of the plants or seeds they are interested in – perhaps only a few out of hundreds or thousands – contain these genes. This forms the basis of marker-assisted breeding, which can help plant breeders halve the time it takes them to breed new high-yielding varieties for acidic soil conditions.
Leon says that GCP provided both projects with the opportunity to validate their discoveries and to use what they had found to develop new aluminium-tolerant sorghum varieties and phosphorus-efficient rice varieties for farmers. But it’s what happened next that made this GCP initiative unique.
Finding the best genes within the crop family
Sorghum, rice, maize and wheat are all part of the Poaceae (true grasses) family, evolving from a common grass ancestor 65 million years ago. Over this time, they have become very different from each other. However, at the genetic level they still have a lot in common.
Over the last 20 years, genetic researchers all over the world have been mapping these cereals’ genomes. These maps are now being used by geneticists and plant breeders to identify similarities and differences between the genes of different cereal species. This process is termed ‘comparative genomics’ and was a fundamental research theme for GCP during its second phase (2008–2014).
“The objective during GCP Phase I (2004-2007) was to study the genomes of important crops and identify genes conferring resistance or tolerance to various stresses, such as drought,” says Rajeev Varshney, Director of the Center of Excellence in Genomics at the International Crops Research Institute for the Semi-Arid Tropics (ICRISAT). “This research was long and intensive, but it set a firm foundation for the work in GCP’s second phase, which sought to use what we have learnt in the laboratory and apply it to breed better varieties of crops.”
Rajeev oversaw GCP’s comparative genomics research projects on aluminium tolerance and phosphorus deficiency in sorghum, maize and rice, as part of his GCP role as Leader of the Comparative and Applied Genomics Research Theme.
“The idea behind the sorghum, maize and rice initiative was to use the discoveries we had independently made in sorghum and rice to see if we could find the same genes in the other crop,” explains Rajeev. “In other words, we wanted to see if we could find PSTOL1 in sorghum and SbMATE in rice.”
Working together through a number of comparative genomics projects, the researchers were highly successful in reaching this goal, discovering valuable sister genes and beginning to introduce them into new improved crop varieties for farmers.
Extending research in sorghum and rice to maize
Researchers at Cornell and EMBRAPA had already been using similar comparative techniques to look for SbMATE in maize because of its close familial connection to sorghum. This research was overseen by Leon and another EMBRAPA researcher, Claudia Guimarães.
“We used the knowledge that Jurandir and Leon’s SbMATE project produced to prove that we had a major aluminium-tolerance gene,” reflects Claudia.
The SbMATE gene in sorghum explains about 80 percent of its aluminium tolerance, but Claudia says that in maize it explains only about 20 per cent, making it harder for researchers to find without a little help knowing what to look for. “So we had to dig a little deeper for other similar genes that confer aluminium tolerance, and we found ZmMATE.”
Maize trials in the field at EMBRAPA. The maize plants on the left are aluminium-tolerant while those on the right are not.
ZmMATE1 has a similar genetic sequence to SbMATE and encodes a similar protein membrane transporter that releases citric acid from the roots. Just as in sorghum, citric acid binds to aluminium in the soil, making it difficult for it to enter plant roots. The team have also discovered related gene ZmMATE2, which also encodes a transporter protein, but appears to confer aluminium tolerance via a different mechanism, as yet unclear.
Claudia has developed a number of molecular markers for ZmMATE, which have been successfully used by breeders at EMBRAPA as well as by African partners in Niger and Kenya, such as Samuel Gudu, to identify maize breeding lines that have the gene.
“We used aluminium-tolerant maize varieties sourced locally and from Brazil to develop a range of potential new varieties,” says Samuel. “The goal is to develop varieties that are suited to our environment and not too dissimilar to varieties that Kenyan farmers like to grow, except they have a higher tolerance to aluminium toxicity.”
Left to right (foreground): Leon Kochian, Jurandir Magalhães and Samuel Gudu examine crosses between Kenyan and Brazilian maize, at the Kenya Agricultural Research Institute (KARI), Kitale, in May 2010.
Involving farmers in the crop breeding process is an important part of such programs being successful, explains Samuel. “They help us identify maize varieties that they have observed have higher tolerance to acidic soils. We also try to incorporate other features that they want, such as disease resistance and higher yield. By incorporating their feedback into the breeding process they are more likely to grow any new varieties, as they have played a part in their development.”
Samuel says they have developed some local aluminium-tolerant varieties, which rank among the best for aluminium tolerance. Interestingly, these varieties seem to have a different aluminium-tolerance mechanism to the Brazilian varieties.
“From the work Samuel has done, we’ve possibly identified a novel source of aluminium tolerance in Kenyan maize varieties,” says Claudia. “We are now working together with Leon to identify the genes that are conferring this tolerance so we can develop markers to help Kenyan maize breeders also identify these varieties more efficiently.”
To help in the process, Samuel and his team are developing single-cross hybrids with a combination of both the novel Kenyan sources of aluminium tolerance and ZmMATE from Brazil, which will be even more tolerant to acidic soils.
Breeding for multiple stresses is a step-by-step process
Suradiyo, a farmer from Bojong Village near Yogyakarta, Indonesia, harvests rice.
In Asia, about 60 percent of rainfed rice is grown on soils that are affected by multiple stresses. These typically include phosphorus deficiency as well as aluminium toxicity, salinity and drought.
These stresses are particularly hard felt in Indonesia, which is the world’s third-largest rice producer. Joko Prasetiyono is a molecular rice breeder at the Indonesian Center for Agricultural Biotechnology and Genetic Resources Research and Development (ICABIOGRAD). His team have been collaborating with IRRI and JIRCAS for many years and contributed to validating the effect of Pup1 by embedding it into three popular local rice varieties – Dodokan, Situ Bagendit and Batur – which were then able to tolerate phosphorus-deficient conditions.
“The aim [with GCP research] was to breed varieties identical to those that farmers already know and trust, except that they have PSTOL1 and an improved ability to take up soil phosphorus,” says Joko.
Joko says that these varieties – which will be available in one to two years – will yield as well as, if not better than, traditional varieties, and will need 30–50 percent less fertiliser.
But the work is only partly finished for Joko and his Asian partners. They are now building on previous work done at Cornell and EMBRAPA to include the SbMATE gene in their varieties. “Higher yields will only be possible if the plant can also tolerate excess aluminium, which severely inhibits root growth and thereby water and nutrient uptake,” explains Joko. “We are also looking at incorporating salt-tolerance and drought-tolerance genes. It’s a step-by-step process where we hope to build tolerance to the multiple stresses that afflict most rice-growing areas throughout Asia and the world.”
Introducing PSTOL1 into maize and sorghum
At EMBRAPA, Claudia is also interested in building up tolerance to multiple stresses and was involved in the project to look for genes similar to PSTOL1 in maize. “As soon as IRRI and JIRCAS had cloned the gene and created markers, we started using the markers to search for the gene in maize, as Jurandir did in sorghum,” she says.
Women farmers in India bring home their sorghum harvest.
Finding genes that confer phosphorus-efficiency traits in maize and sorghum has been a more challenging project, according to Leon. “From the rice work, we knew a big part of phosphorus efficiency was to do with root architecture – you want to have shallow horizontal roots instead of roots that grow down, which is often the case in maize and sorghum,” he explains. “This is because there is less accessible phosphorus further down the soil profile.”
Observing root architecture is difficult in ordinary soil, so the team had to develop new ways to visualise the plants’ roots. They grew plants in a transparent nutrient gel, which they then photographed to create three-dimensional images of the root structure.
The team found sorghum and maize varieties that contained genes similar to PSTOL1 in rice, but which also have longer root systems that radiated outwards rather than downwards in gels with higher concentration of aluminium. “These observations helped validate multiple PSTOL1 regions in sorghum and maize, which we’ve been able to develop markers for to help breeders identify these traits more easily,” says Leon.
These markers have successfully been used by sorghum breeders in Brazil and Africa to identify phosphorus-efficient varieties. Maize breeders in both Brazil and Africa are expected to use similar markers to validate their varieties in 2015.
New sorghum varieties prove their worth in the field
Eva Weltzien is one Africa-based sorghum breeder who has benefited from these PSTOL1 and SbMATE markers. Based in Mali at ICRISAT, Eva and her team have been using the markers to select for aluminium-tolerant and phosphorus-efficient varieties and validating their performance in field trials across 29 environments in three countries in West Africa.
She says the markers have helped evolve the way they do their breeding. “Using molecular markers, we are able to identify whether the lines we are breeding have genes that confer the traits that we want,” explains Eva. “It has really revolutionised our breeding program and helped it make great progress in the past three to four years.”
In Mali, sorghum is an important staple crop. It is used to make tô (a thick porridge), couscous, and local beers. Part of its popularity is its adaptability to various climates – in Mali it is grown in very dry environments as well as in forest/rainforest zones. However, it is widely affected by acidic soils.
Sorghum farmers at work in the field in Mali.
“Low phosphorus availability is a key problem for farmers on the coast of West Africa, and breeding phosphorus-efficient crops to cope with these conditions has been a main objective of ICRISAT in West Africa for some time,” says Eva.
“We’ve had good results in terms of field trials. We have at least 20 lines we are field testing at the moment, which we selected from 1,100 lines that we tested under high and low phosphorous conditions.” Eva says that some of these lines could be released as new varieties as early as next year.
“Overall, we feel the GCP partnership with EMBRAPA and Cornell is enhancing our capacity here in Mali, and that we are closer to delivering more robust sorghum varieties that will help farmers and feed the ever-growing population in West Africa.”
Leon notes that the work by Eva in Mali and by other African partners in Niger and Kenya is imperative for the research. “Just because plants have these genes, doesn’t mean they will all display aluminium tolerance or phosphorus efficiency. You still need to test and observe for these traits in the field and determine what other factors might affect plants grown in acidic soils.”
One surprising observation that has Leon intrigued is a local sorghum variety with a phosphorus-efficiency gene that is close to where the SbMATE gene resides in the sorghum genome. “This suggests that SbMATE, which aids with aluminium tolerance, may also improve phosphorus efficiency. This means we could use SbMATE markers to look for both phosphorus efficiency and aluminium tolerance,” he says. Leon and Jurandir will continue to validate this result post-GCP.
Working together to improve food security worldwide
GCP’s comparative genomics projects have laid a significant foundation for further research into and breeding for tolerance to multiple plant stresses.
A Kenyan farmer in her maize field.
“We’re in a golden age of biology where we are learning more and more about the complexities and commonalities of plants, which is allowing us to manipulate them ever so slightly to help them tolerate multiple environmental stresses,” says Leon. “As a geneticist, I am extremely proud to be part of this, particularly seeing the potential impact that the basic research we do in the laboratory can have on crop improvement and the lives of people in poorer countries.”
Although not all projects produced new and improved varieties ready for release, they are well and truly in the pipeline. Each partner institute is committed to work together and source new funding to continue on their quest to produce further products.
“GCP has really installed in us a spirit to see this work through and expand on it,” says Leon. “I mean, we are now working with other countries and institutes to share what we have learnt with them and help them make the discoveries that we have. It’s a credit to GCP for bringing us all together; that was a key to the success of the project. Each partner has brought their expertise to the table – genomics, molecular biology, plant breeding – and it has been great to see the impact filter into Africa and Asia.”
In Kenya, Samuel agrees with Leon’s assessment. “GCP gave us an opportunity to build our expertise and start interacting with the rest of the world,” he says. “But more importantly, it means that we’re contributing to food security in Kenya, and that makes us really proud.”
Although the sun is setting on GCP, work on comparative genomics projects is still in progress, with all parties still working towards delivering important new acid-beating varieties to farmers.
A boy rides his bicycle next to a rice field in the Philippines. With acid soils affecting half the world’s current arable land, acid-beating crop varieties will help farmers feed their families – and the world – into the future.
