Characterisation and diversity of Pyrenophora teres f. maculata isolates in Western Australia

Spot type net blotch caused by Pyrenophora teres f. maculata (Ptm) has become a prominent disease in Western Australia, as has also occurred elsewhere. The disease has a negative impact on both grain yield and quality resulting from reduced grain size. Lack of resistance and stubble retention are the likely factors in the increased severity of the disease in barley growing areas of Western Australia. Because of the increasing importance of spot type net blotch and the need to improve barley resistance, understanding pathogen virulence is a high priority as this has direct impact on the identification and utilization of resistance genes in breeding programs. Ninety nine isolates of Ptm were collected from geographically dispersed barley fields of Western Australia during 2001 and 2002. Forty nine sporulating isolates of Ptm were classified into seven isolate groups (IGs) on the basis of their infection responses on 26 differential barley lines. The 26 lines were likewise classified into four line groups (LGs) based on their distinguishing response to the spot type net blotch isolates. The varied infection responses among the differential barley lines demonstrated a wide geographic dispersal of IGs as well as previously undetected virulence in Ptm in Western Australia. The commercially grown barley cultivars Baudin and Gairdner are regarded as susceptible to spot type net blotch, but showed a range of reactions to the various Ptm isolates as seedling plants. The variability in the pathogen and the resistance identified in some genotypes used in this study are being investigated further to develop superior, adapted germplasm for use in barley breeding programs in Australia.