Genetic variation for virulence and RFLP markers in Pyrenophora teres

Pyrenophora teres f. teres (causing net blotch) and Pyrenophora teres f. maculata (causing "spot form" of the disease) are important foliar pathogens of barley. In breeding for resistance to disease, it is important to have a thorough knowledge of the degree of genetic variation in the pathogen. This study was undertaken to assess genetic variation in a small, but geographically diverse collection of P. teres isolates. Isolates derived from single conidia were evaluated for their virulence phenotypes on 25 differential barley genotypes. Fifteen pathotypes were identified from a collection of 23 P. t. f. teres isolates, and 4 pathotypes, from a collection of 8 P. t. f. maculata isolates. In general, the P. t. f. teres isolates exhibited a broader spectrum and a higher level of virulence on the host differentials than the P. t. f. maculata isolates. Eight barley genotypes were resistant to all 19 pathotypes identified and should be useful in breeding barley for resistance to both forms of P. teres. Genetic variation was also examined by restriction fragment length polymorphism (RFLP) analysis. A 0.46-kb DNA fragment (ND218) generated by the polymerase chain reaction from genomic DNA of a California isolate of P. t. f. teres was used as a probe. Every P. teres isolate tested with ND218 exhibited a unique RFLP pattern. Cluster analysis, based on both the virulence phenotypes and RFLP patterns, indicates that P. teres possesses a high degree of diversity at the species and subspecies levels. The high degree of polymorphism revealed by ND218 will make this probe a useful tool for the DNA fingerprinting of P. teres isolates.