Wang SG, Jia SS, Sun DZ, Wang HY, Dong FF, Ma HX, Jing RL and Ma G (2015). Genetic basis of traits related to stomatal conductance in wheat cultivars in response to drought stress. Photosynthetica 53(2):299–305 (DOI: 10.1007/s11099-015-0114-5). Not open access; view abstract. (G7010.02.01)

Leal-Bertioli S, Shirasawa K, Abernathy B, Moretzsohn M, Chavarro C, Clevenger J, Ozias-Akins P, Jackson S and Bertioli D (2015). Tetrasomic recombination is surprisingly frequent in allotetraploid Arachis. Genetics 199(4):1093–1105 (DOI: 10.1534/genetics.115.174607). (G6010.01)

Abstract: Arachis hypogaea L. (cultivated peanut) is an allotetraploid (2n = 4x = 40) with an AABB genome type. Based on cytogenetic studies it has been assumed that peanut and wild-derived induced AABB allotetraploids have classic allotetraploid genetic behavior with diploid-like disomic recombination only between homologous chromosomes, at the exclusion of recombination between homeologous chromosomes. Using this assumption, numerous linkage map and quantitative trait loci studies have been carried out. Here, with a systematic analysis of genotyping and gene expression data, we show that this assumption is not entirely valid. In fact, autotetraploid-like tetrasomic recombination is surprisingly frequent in recombinant inbred lines generated from a cross of cultivated peanut and an induced allotetraploid derived from peanut's most probable ancestral species. We suggest that a better, more predictive genetic model for peanut is that of a "segmental allotetraploid" with partly disomic, partly tetrasomic genetic behavior. This intermediate genetic behavior has probably had a previously overseen, but significant, impact on the genome and genetics of cultivated peanut.

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Leiser WL, Rattunde HFW, Piepho H-P, Weltzien E, Diallo A, Toure A and Hausmann BIG (2015). Phosphorous efficiency and tolerance traits for selection of sorghum for performance in phosphorous-limited environments. Crop Science 55 Published online: 27 March 2015 (DOI: 10.2135/cropsci2014.05.0392). (G7010.03.03)

Abstract: Sorghum (Sorghum bicolor (L.) Moench) is widely cultivated in West Africa (WA) on soils with low phosphorus (P) availability. Large genetic variation for grain yield (GY) under low-P conditions was observed among WA sorghum genotypes, but information is lacking on the usefulness of P-tolerance ratios (relative performance in –P [no P fertilizer] vs. +P [with P fertilizer] conditions) and measures of P-acquisition and internal P-use efficiency as selection criteria for enhancing GY under low-P conditions. We evaluated 70 WA sorghum genotypes for GY performance under −P and +P conditions for 5 yr in two locations in Mali and assessed P acquisition (e.g., P content in biomass) and P-use efficiency (e.g., grain produced per unit P uptake) traits under −P and +P conditions in one site in 2010. Significant genetic variation existed for all P-tolerance ratios across multiple sites. Photoperiod-sensitive landrace genotypes showed significantly better P tolerance and less delay of heading under P-limited conditions compared with photoperiod-insensitive varieties. Genotypic correlations of P-tolerance ratios to GY under −P were moderate. Phosphorous acquisition and P-use efficiency traits independent of harvest index were of similar importance for GY under −P conditions in statistically independent trials. However grain-P and stover-P concentrations from one −P trial showed only weak correlations with GYs in statistically independent trials. Highest predicted gains for −P GY were obtained by theoretical index selection based on −P GY combined with P-use efficiency traits (e.g., low-grain P concentration). Such index selection is expected to achieve both increased sorghum productivity and P sustainability in the P-limited WA production systems.

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Pratt RC, Holland JB, Balint-Kurti PJ, Coles ND, Zwonitzer JC, Casey MA and McMullens MC (2015). Registration of the Ki14 × B73 recombinant inbred mapping population of maize. Journal of Plant Registrations 9(2):262–265 (DOI: 10.3198/jpr2014.06.0041crmp). Not open access; view abstract.

Leal-Bertioli SCM, Santos SP, Dantas KM, Inglis PW, Nielen S, Araujo ACG, Silva JP, Cavalcante U, Guimarães PM, Brasileiro ACM, Carrasquilla-Garcia N, Penmetsa RV, Cook D, Moretzsohn MC and Bertioli DJ (2015). Arachis batizocoi: a study of its relationship to cultivated peanut (A. hypogaea) and its potential for introgression of wild genes into the peanut crop using induced allotetraploids. Annals of Botany 115(2):237–49 (DOI: 10.1093/aob/mcu237). First published online in December 2014. (G6010.01)

Abstract: Background and Aims Arachis batizocoi is a wild relative of cultivated peanut (A. hypogaea), an allotetraploid with an AABB genome. Arachis batizocoi was once considered the ancestral donor of the peanut B genome, but cytogenetics and DNA phylogenies have indicated a new genome classification, ‘K’. These observations seem inconsistent with genetic studies and breeding that have shown that A. batizocoi can behave as a B genome.

Methods The genetic behaviour, genome composition and phylogenetic position of A. batizocoi were studied using controlled hybridizations, induced tetraploidy, whole-genome in situ fluorescent hybridization (GISH) and molecular phylogenetics.

Key Results Sterile diploid hybrids containing AK genomes were obtained using A. batizocoi and the A genome species A. duranensis, A. stenosperma, A. correntina or A. villosa. From these, three types of AAKK allotetraploids were obtained, each in multiple independent polyploidy events. Induced allotetraploids were vigorous and fertile, and were hybridized to A. hypogaea to produce F1 hybrids. Even with the same parental combination, fertility of these F1 hybrids varied greatly, suggesting the influence of stochastic genetic or epigenetic events. Interestingly, hybrids with A. hypogaea ssp. hypogaea were significantly more fertile than those with the subspecies fastigiata. GISH in cultivated × induced allotetraploids hybrids (harbouring AABK genomes) and a molecular phylogeny using 16 intron sequences showed that the K genome is distinct, but more closely related to the B than to the A genome.

Conclusions The K genome of A. batizocoi is more related to B than to the A genome, but is distinct. As such, when incorporated in an induced allotetraploid (AAKK) it can behave as a B genome in crosses with peanut. However, the fertility of hybrids and their progeny depends upon the compatibility of the A genome interactions. The genetic distinctness of A. batizocoi makes it an important source of allelic diversity in itself, especially in crosses involving A. hypogaea ssp. hypogaea.

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Purushothaman R, Thudi M, Krishnamurthy L, Upadhyaya HD, Kashiwagi J, Gowda CLL and Varshney RK (2015). Association of mid-reproductive stage canopy temperature depression with the molecular markers and grain yields of chickpea (Cicer arietinum L.) germplasm under terminal drought. Field Crops Research 174:1–11 (DOI: 10.1016/j.fcr.2015.01.007). (G4008-12)

Abstract: Canopy temperature depression (CTD) has been used to estimate crop yield and drought tolerance. However, when to measure CTD for the best breeding selection efficacy has seldom been addressed. The objectives of this study were to evaluate CTD as a drought response measure, identify suitable crop stage for measurement and associated molecular markers. CTD was measured using an infrared camera on 59, 62, 69, 73, 76 and 82 days after sowing (DAS) and the grain yield, shoot biomass and harvest index (%). CTD recorded at 62 DAS was positively associated with the grain yield by 40% and shoot biomass by 27% and such association diminished gradually to minimum after 76 DAS. Moreover, CTD at 62 DAS also showed similar positive association with the grain yield recorded in two previous years (r = 0.45***, 0.42***). Genome-wide and candidate gene based association analysis had revealed the presence of nine SSR, 11 DArT and three gene-based markers that varied across the six stages of observation. Two SSR markers were associated with CTD through crop phenology or grain yield while the rest were associated only with CTD for computing marker-trait associations (MTAs). The phenotypic variation explained by the markers was the highest at 62 DAS. These results confirm the importance of continued transpiration and the ability of the roots to supply stored soil water under terminal drought. The selection for grain yield through CTD is done best 15 days after the mean flowering time.

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Leiser WL, Olatoye MO, Rattunde HFW, Neumann G, Weltzien E and Haussmann BIG (2015). No need to breed for enhanced colonization by arbuscular mycorrhizal fungi to improve low-P adaptation of West African sorghums. Plant and Soil Published online: 14 March 2015 (DOI: 10.1007/s11104-015-2437-1). Not open access; view abstract. (G7010.03.03)

Keller B, Manzanares C, Jara C, Lobaton JD, Studer B and Raatz B (2015). Fine-mapping of a major QTL controlling angular leaf spot resistance in common bean (Phaseolus vulgaris L.). Theoretical and Applied Genetics 128(5):813–826 (DOI: 10.1007/s00122-015-2472-6). (G6010.03)

Key message: A major QTL for angular leaf spot resistance in the common bean accession G5686 was fine-mapped to a region containing 36 candidate genes. Markers have been developed for marker-assisted selection.

Abstract: Common bean (Phaseolus vulgaris L.) is an important grain legume and an essential protein source for human nutrition in developing countries. Angular leaf spot (ALS) caused by the pathogen Pseudocercospora griseola (Sacc.) Crous and U. Braun is responsible for severe yield losses of up to 80 %. Breeding for resistant cultivars is the most ecological and economical means to control ALS and is particularly important for yield stability in low-input agriculture. Here, we report on a fine-mapping approach of a major quantitative trait locus (QTL) ALS4.1^{GS, UC} for ALS resistance in a mapping population derived from the resistant genotype G5686 and the susceptible cultivar Sprite. 180 F₃ individuals of the mapping population were evaluated for ALS resistance and genotyped with 22 markers distributed over 11 genome regions colocating with previously reported QTL for ALS resistance. Multiple QTL analysis identified three QTL regions, including one major QTL on chromosome Pv04 at 43.7 Mbp explaining over 75 % of the observed variation for ALS resistance. Additional evaluation of 153 F₄, 89 BC₁F₂ and 139 F₄/F₅/BC₁F₃ descendants with markers in the region of the major QTL delimited the region to 418 kbp harboring 36 candidate genes. Among these, 11 serine/threonine protein kinases arranged in a repetitive array constitute promising candidate genes for controlling ALS resistance. Single nucleotide polymorphism markers cosegregating with the major QTL for ALS resistance have been developed and constitute the basis for marker-assisted introgression of ALS resistance into advanced breeding germplasm of common bean.

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Zhang L, Li H and Wang J (2015). Linkage analysis and map construction in genetic populations of clonal F1 and double cross. G3 5(3):427–439 (DOI:10.1534/g3.114.016022). (G8009.10)

Abstract: In this study, we considered four categories of molecular markers based on the number of distinguishable alleles at the marker locus and the number of distinguishable genotypes in clonal F1 progenies. For two marker loci, there are nine scenarios that allow the estimation of female, male, and/or combined recombination frequencies. In a double cross population derived from four inbred lines, five categories of markers are classified and another five scenarios are present for recombination frequency estimation. Theoretical frequencies of identifiable genotypes were given for each scenario, from which the maximum likelihood estimates of one or more of the three recombination frequencies could be estimated. If there was no analytic solution, then Newton-Raphson method was used to acquire a numerical solution. We then proposed to use an algorithm in Traveling Salesman Problem to determine the marker order. Finally, we proposed a procedure to build the two haploids of the female parent and the two haploids of the male parent in clonal F1. Once the four haploids were built, clonal F1 hybrids could be exactly regarded as a double cross population. Efficiency of the proposed methods was demonstrated in simulated clonal F1 populations and one actual maize double cross. Extensive comparisons with software JoinMap4.1, OneMap, and R/qtl show that the methodology proposed in this article can build more accurate linkage maps in less time.

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Azam F, Chang X and Jing R (2015). Mapping QTL for chlorophyll fluorescence kinetics parameters at seedling stage as indicators of heat tolerance in wheat. Euphytica 202(2):245–258 (DOI: 10.1007/s10681-014-1283-1). First published online in October 2014. (G7010.02.01)

Abstract: High temperature or heat stress is one of the most important abiotic stresses that affect wheat production in almost every part of the world. Parameters of chlorophyll fluorescence kinetics (PCFKs) are the most powerful and reliable characters available to understand the impact of various abiotic stresses on plant physiological processes and heat tolerance. The present research was aimed to identify genomic regions controlling PCFKs at early growth stages of wheat through quantitative trait loci analysis by applying heat stress for different duration of time. A doubled haploid population derived from the cross of two Chinese wheat cultivars Hanxuan 10 and Lumai 14 was exposed to 38 °C for 2, 4, 6 and 8 h of heat stress and PCFKs (initial fluorescence, maximum fluorescence, variable fluorescence and maximum quantum efficiency of photosystem II) were measured. A total of 37 QTLs were identified for the target traits, among which 13 were detected under normal temperature of 25 °C and the remaining 24 under the stressful temperature of 38 °C. Stable or consistently expressed QTLs for initial, maximum and variable fluorescence were detected on chromosomes 1A, 1B, 2B, 4A and 7D. In addition, 24 QTLs were clustered in 9 clusters on chromosomes 1A, 1B, 2B, 3B, 3D, 4A, 5A and 7D. These QTL hot spot regions along with stable QTLs should be targeted for better understanding the genetic basis of chlorophyll fluorescence kinetics parameters in future mapping studies.

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