Durum wheat (Triticum durum Desf.) is a major stable crop and it represents a base of the Mediterranean diet. This region is subject to a Mediterranean climate, which is extremely unpredictable with severe changes in moisture and temperature occurring each crop season. This unpredictability is summarized by breeders as GxE and the identification of traits controlling this interaction is quintessential to ensure stability in production season after season. To study the genetics of yield stability, four RILs populations derived from elite x elite crosses were assessed for yield and 1,000-kernel weights across five diverging environments in Morocco and Lebanon. These 550 RILs were characterized with 4,909 polymorphic SNPs via genotyping by sequencing. A consensus map was derived by merging the individual genetic maps of each population. Finally, imputation was used to fill all the missing haplotypes and reach a reduction of missing data to below 8%. Several significant QTLs were identified to be linked to TKW, grain yield and a stability index, namely AMMI wide adaptation index (AWAI). A second approach to identify loci controlling stability was the use of a global panel of 288 elites, accessions and landraces tested in 15 diverging environment. Multi-locations data were compiled via GxE models to derive the AWAI stability index. In addition, this panel was characterized with 8,173 polymorphic SNPs via Axiom 35K array. Significant associations were identified for all traits, including QTLs unique to AWAI. The sum of the identified QTLs can now be pyramid via marker assisted selection and molecular designed crosses in order to obtain very stable cultivars.
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Intensive breeding and replacement of traditional landraces by modern cultivars led to the narrowing of genetic variation in cultivated wheat. The most sustainable method for wheat improvement is utilization of genetic diversity from wheat wild relatives such as Aegilops speltoides that has a diversity of genes for resistance to leaf rust (LR). A high pairing-inducing Ae. speltoides strain collected from Israel was introgressed into T. turgidum subsp. durum var. landrace Nursi. The F1 plants were treated with colchicine to induce chromosome doubling. The resulting hexaploid plants were crossed to bread wheat cv. Beit-Lehem and F3 plants were backcrossed three times to bread wheat cv. Barnir. Each generation was selected for LR resistance to P. triticina isolate #1010 and five resistant wheat-Ae. speltoides introgression lines (ILs) designated DK1 to DK5 were selected. These Ae. speltoides ILs were genotyped using the 90K Infinium SNP assay and most of the polymorphic markers were mapped to chromosome 1B suggesting that the Ae. speltoides introgressions encompass most of this chromosome. To test if the newly identified gene is identical to Lr51, that was also introgressed from Ae. speltoides to chromosome 1B of bread wheat, the DK ILs were genotyped with the molecular marker AGA7 that was shown to be linked to Lr51. The Ae. speltoides AGA7 allele was absent in the DK ILs suggesting that these genotypes are not carrying the Lr51 introgression. Moreover, we performed an allelism test. Spring wheat cv. Kern harboring resistance gene Lr51 was crossed with DK2 and an F2 segregation ratio of 15R:1S was obtained, indicating that the resistance was conditioned by two independent dominant genes. Overall, our results suggest that DK2 carries a new leaf rust resistance gene from Ae. speltoides and this gene has potential for wheat improvement.
Stripe rust (Puccinia striiformis f. sp. tritici) is a devastating disease of wheat production world-wide. Yr5 is a race-specific resistance gene effective to all races which have been identified in the U.S. Therefore, it has been increasingly used for cultivar development in the U.S. The goal of this study was to identify “breeder friendly” SNP markers associated with Yr5 through linkage mapping in a spring wheat recombinant inbred line (RIL) population and validate these markers with an additional RIL population, Pacific Northwest (PNW) wheat elite breeding materials, and a world-wide collection of spring wheat. RIL populations were developed from a cross between moderately susceptible experimental line WA8149 and two elite Yr5 donors, S0900317 and S0900163. Seventy PNW spring and winter wheat lines either carrying Yr5 or not, and 3,040 hexaploid spring wheat lines from a world-wide collection were used to further validate flanking markers for Yr5. Seedling resistance response to isolates Pstv-37 and Pstv-51 was evaluated for these RIL populations. These RILs were genotyped with 46 KASP markers located on chromosome 2B in addition to previously reported Yr5 linked markers, wmc175 (Murphy et al. 2009) and TaAffix65234.1.S1_at (McGrann et al. 2014). Linkage mapping was conducted by MapDisto v1.7.5. A total 10 markers localized Yr5 within 0.7 cM chromosome region in the WA8149/S0900317 population of 300 RILs. The same set of markers also localized Yr5 within 3 cM chromosome region in the WA8149/S0900163 population of 274 RILs. Newly identified KASP markers were closer to Yr5 than wmc175 and TaAffix65234.1.S1_at in these two populations. These markers were further validated with PNW winter and spring wheat and a world-wide collection of spring wheat. These KASP markers flanking Yr5 reliably selected for germplasm carrying Yr5 and will assist in pyramiding different resistances into breeding lines to develop more durable stripe rust resistant cultivars.