Reaction of Global Collection of Rye ( L.) to Tan Spot and Races in South Dakota.

Rye ( L.) serves as an alternative host of () the cause of tan spot on wheat. Rye is cultivated as a forage or cover crop and overlaps with a significant portion of wheat acreage in the U.S. northern Great Plains; however, it is not known whether the rye crop influences the evolution of races. We evaluated a global collection of 211 rye accessions against tan spot and assessed the diversity in population on rye in South Dakota. All the rye genotypes were inoculated with races 1 and 5, and infiltrated with Ptr ToxA and Ptr ToxB, at seedling stage. We observed 21% of the genotypes exhibited susceptibility to race 1, whereas, 39% were susceptible to race 5. All 211 accessions were insensitive to both the Ptr toxins. It indicates that though rye exhibits diversity in reaction to tan spot, it lacks and sensitivity genes. This suggests that unknown toxins or other factors can lead to establishment in rye. We characterized the race structure of 103 isolates recovered from rye in South Dakota. Only 22% of the isolates amplified gene and were identified as race 1 based on their phenotypic reaction on the differential set. The remaining 80 isolates were noted to be race 4. Our results show that races 1 and 4 are prevalent on rye in South Dakota with a higher frequency of race 4, suggesting a minimal role of rye in the disease epidemiology.