WHEAT LANDRACES FOR NOVEL RESISTANCE TO BIOTIC AND ABIOTIC STRESSES
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Wheat production around the world is challenged by various plant diseases and unfavorable environmental conditions. Wheat landraces from diverse geographic regions are sources of unexploited genetic diversity that can be introduced into modern wheat-breeding programs in search of novel resistance to biotic and abiotic stresses. Stripe rust, caused by Puccinia striiformis f. sp. tritici (Pst), and stem rust, caused by P. graminis f. sp. tritici are economically important diseases of wheat. A total of 652 landraces previously screened for resistance to stem rust using race TTKSK (Ug99) were tested for resistance to current races of Pst. Resistance to stripe rust was observed in 165 landraces, among which 30 also had resistance to stem rust. Genetic analysis based on single-nucleotide polymorphism (SNP) grouped resistant landraces into different clusters, and principal coordinates analyses (PCoA) identified genetically distinct resistant genotypes indicating potentially diverse resistance genes.Four landraces with resistance to both stripe and stem rusts were crossed with a susceptible spring wheat genotype, “Avocet Susceptible�, to develop F6 recombinant inbred lines. The populations were phenotyped for stripe rust and genotyped with genotyping-by-sequencing and microsatellites to map quantitative trait loci (QTL) for resistance. A major QTL, Qyr.PI 480035-1B on chromosome 1B, was associated with resistance in landrace PI 480035. QTL were identified from PI 388082 on 2B, 3B, 3DS, 5BL, and 7B, from PI 250408 on 5B and 7B, and from PI 119350 on 1B and 3AS.A cluster of 553 winter wheat landraces from regions with latitudes higher than 40°N was identified in PCoA based on SNPs. A freezing tolerance test was performed using electrolyte leakage on 192 landraces at temperatures -14, -16, and -18°C. The regression analysis showed a significant negative correlation of latitude and electrolyte leakage with an R2 of 0.14, (P < 0.0001), indicating greater freezing tolerance in landraces from higher latitudes. Genome-wide association studies identified regions on 4A and 6A contributing to the adaptation to higher latitudes and conferring freezing tolerance, respectively. Landraces with resistance to wheat rusts and freezing tolerance have regional and global importance as sources to develop diverse germplasm for mitigating the biotic and abiotic challenges.