The Development and Validation of a Specific Marker for the Emerging V5-Virulent Race of <i>Puccinia striiformis</i> f. sp. <i>tritici</i>

The emergence of new Puccinia striiformis f. sp. tritici races is responsible for rendering wheat varieties with race-specific resistance susceptible and causing stripe rust epidemics. The conventional methods for virulent races time-consuming facility specific, and skill-dependent. In contrast, molecular markers cloud be used to efficiently detect special races of interesting. In China, a newly-emerged race group (V5), with virulence to resistance gene Yr5, is becoming a threat to wheat production as the gene has been intensively used in breeding programs and the race is also virulent to many other resistance genes. For timely monitoring the dynamics of this race and assessing its early potential risk, we developed a sequence characterized amplified regions (SCAR) marker V5F/V5R specific for the V5 race groups. The marker can be amplified in DNA concentration as little as 100 pg/μL. It also can be detected from a wheat leaf segment as early as 5 days after inoculation with 192 urediniospores on 5-cm long leaf segments or from a 1-cm leaf segment 6 days after inoculation with a single-urediniospore. Among 140 isolates from five provinces (Gansu, Shaanxi, Qinghai, Xizang, and Xinjiang) tested with the marker, 3.6% of the isolates were marker positive and virulent on the tested Yr5-carrying wheat genotypes. The results indicate that the V5-specific marker can be used for rapidly and accurately detecting the V5 race groups. The information on the race frequency and distribution is useful for breeding programs to develop wheat cultivars with effective resistance for managing stripe rust.