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Grain number is a major trait for wheat yield under dryland farming. An International Triticeae Mapping Initiative (ITMI) mapping population comprising 105 recombinant inbred lines (RIL) developed from a cross between a Synthetic hexaploid wheat (Triticum aestivum) ‘W7984’ and a spring wheat variety ‘Opata M85’ was used to identify quantitative trait loci (QTL) associated with grain number per spike under two treatment conditions, normal watering and water stress during meiosis. Two major QTL for grain number per spike on the main stem Q.Gnu.uwa-5A-1 and Q.Gnu.uwa-5A-2 with phenotypic variations of 25.71% and 24.93%, respectively, were detected on the long arm of chromosome 5A when plants were exposed to water stress during meiosis. One QTL (Q.Gnu.uwa-2A) with a LOD score of 2.8 was detected on the long arm of chromosome 2A under normal watering condition. The alleles associated with higher grain number per spike under different treatment conditions came from the Synthetic W7984 parent. Two populations developed from crosses Synthetic W7984 × Lang and Synthetic W7984 × Westonia were used to validate the identified QTL under water stress during meiosis. SSR markers Xbarc230 and Xbarc319 linked with the identified QTL on chromosome 5AL were validated in the two F2:4 segregating populations. These closely linked SSR markers could potentially be utilized in marker-assisted selection to reduce yield loss in regions where water stress during meiosis occurs frequently. The identified QTL can be incorporated into elite lines / cultivars to improve wheat grain yield. [ABSTRACT FROM AUTHOR]

Water stress during meiosis in wheat is a major constraint to yield especially for the rainfed farming regions. Pollen sterility has been proposed as the most sensitive process leading to low seed set (low % of fertile spikelets), but here we show this is not universal, and that the development of female reproductive parts is equally if not more sensitive than male parts in many wheat cultivars. The first experiment examined water stress during meiosis in 46 wheat genotypes. The reduction in seed set varied widely, ranging from 6 to 48%. The second experiment differentiated the effect of water stress on the male or the female reproductive part in 13 wheat genotypes. Water stress was imposed during meiosis, with plants cross-pollinated 5 days later with pollen from stressed or unstressed plants used to pollinate emasculated stressed or unstressed female parts. Seed set and kernel weight were measured at maturity. Contrary to the well-held view that the male reproductive part is the major contributor to seed set reduction when water stress is experienced during meiosis, the stressed-female part was also a predominant contributor in four wheat genotypes among the 13 genotypes examined. This strongly indicates that both male and female parts are responsible for yield reduction when waterstressed during meiosis and suggests that it may be possible to breed tolerant wheat cultivars combining tolerance from both male and female reproductive parts. [ABSTRACT FROM AUTHOR]