Quantitative Trait Loci Analysis of Avocet X PavonWheat Population for Resistance to Stem Rust Race Ug99

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Njau,P. N.
Singh,R. P.
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Stem rust of wheat, caused by Puccinia graminis f. sp. tritici, was under control worldwide for over 30 years by utilizing genetic resistance. The emergence of stem rust in 1998 in Eastern Africa in form of the race U g99 and its evolving variants with virulence to many resistance genes has rendered over 80% of the global wheat germ plasm susceptible. In this study, we identified genomic regions contributing to putative durable, adult plant resistance (APR) to wheat stem rust. A recombinant inbred line (RIL) population of298 lines was previously developed at CIMMYT from a cross between 'Avocet S' and 'Pavon 76'. Pavon 76 has been described to carry the "Sr2 gene complex" known to confer APR to stem rust. Avocet S carries the race-specific resistance gene Sr26. A subset of RILs without Sr26 segregated for APR to stem rust race Ug99 when evaluated in Kenya for three years. Single year and joint year analysis by inclusive composite interval mapping using 450 DArT markers identified five quantitative trait loci (QTLs) that contributed to the resistance of wheat to stem rust race U g99. A combination of APR QTLs from the two parents resulted in transgressive segregants expressing higher levels of resistance than Pavon 76. Our results indicate that it is possible to accumulate several minor resistance genes each with a small to intermediate effect resulting in a variety that exhibits negligible disease levels even under high stem rust pressure.
East African Agricultural And Forestry Journal, 78 (No 3), p. 137-142