Genetics and Sources of Stem Rust Resistance in Barley

Stem rust (Puccinia graminis f. sp. tritici) is an important disease of both wheat and barley. Highly virulent African races of stem rust like TTKSK (aka isolate Ug99) are virulent on greater than 90% of the world’s wheat and barley cultivars. There are limited sources of resistance to these races in barley. Many attempts to identify stem rust resistance sources have resulted in limited new sources of resistance. This may have been due to a lack of diversity among previously surveyed collections. To address this problem this study will utilize the USDA National Small Grains Collection barley iCore collection. The collection was screened against African stem rust in Njoro, Kenya for two seasons and in St. Paul, Minnesota against race QCCJB for two seasons. The collection was also evaluated against race TTKSK at the seedling stage in the Biosafety Level-3 containment facility in St. Paul, Minnesota, were about 14% (277) displayed low infection types. In St. Paul in 2013 about 7% (132) displayed high levels of resistance, where as in 2014 a few more show some resistance at a frequency of about 10% (203). In Kenya the frequency of resistance was similar across the main season and the off-season season, with 13% showing high levels of resistance. Association mapping detected several significant loci for the adult plant and seedling reactions; the most interesting was on 5H. This loci has previously been reported in response to adult plant reaction to stem rust infection and will be useful in barley improvement.