Abstract
Stem rust (caused by Puccinia graminis f. sp. tritici) is a major disease of wheat. To understand the genetic basis of stem rust resistance in Nebraska winter wheat, a set of 330 genotypes representing two nurseries (DUP2015 and TRP2015) were evaluated for resistance to a Nebraska stem rust race (QFCSC) in two replications. The TRP2015 nursery was also evaluated for its resistance to an additional 13 stem rust races. The analysis of variance revealed significant variation among genotypes in both populations for stem rust resistance. Nine stem rust genes, Sr6, Sr31, Sr1RSAmigo, Sr24, Sr36, SrTmp, Sr7b, Sr9b, and Sr38, were expected and genotyped using gene-specific markers. The results of genetic analysis confirmed the presence of seven stem rust resistance genes. One genotype (NE15680) contained target alleles for five stem rust resistance genes and had a high level of stem rust resistance against different races. Single marker analysis indicated that Sr24 and Sr38 were highly significantly associated with stem rust resistance in the DUP2015 and TRP2015 nurseries, respectively. Linkage disequilibrium analysis identified the presence of 17 SNPs in high linkage with the Sr38-specific marker. These SNPs potentially tagging the Sr38 gene could be used in marker-assisted selection after validating them in additional genetic backgrounds.
Highlights
Wheat (Triticum aestivum L.) is the third most widely produced crop in the U.S following corn (Zea mays L.) and soybeans (Glycine max (L.) Merr)
As many genes were expected to exist in these nurseries, we looked for the association of minor genes controlling the resistance
Most of the DUP2015 nursery was resistant to race QFCSC with a percentage of 80% of the genotypes (Fig. 1), indicating the historic phenotypic screens and gene pyramiding for stem rust resistance in the breeding program was successful
Summary
Wheat (Triticum aestivum L.) is the third most widely produced crop in the U.S following corn (Zea mays L.) and soybeans (Glycine max (L.) Merr). For the past 70 years, this program has aimed to release new cultivars that meet market needs of grain yield and quality, and stem rust resistance. In this program, crosses between genotypes containing target traits are followed by phenotypic and genotypic selection for improved genotypes[3]. The objectives of this study were to (1) screen a set of 330 Nebraska winter wheat genotypes for resistance to stem rust, (2) identify the possible genes and gene pyramids in the elite genotypes, and (3) select genotypes with pyramided stem rust resistance genes to be used in breeding programs
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