PATHOGENIC VARIATION IN AUSTRALIAN ISOLATES OF MYCOSPHAERELLA-GRAMINICOLA

Seven isolates of Mycosphaerella graminicola gave a range of infection patterns when inoculated onto 20 wheat testers in glasshouse tests. Linear modelling and the biplot technique indicated host-pathogen interaction, hence evidence for physiologic specialization. Two isolates from Western Australia (WA) gave only limited disease on the cultivar Egret which is field resistant in WA. The cw. Heron and Robin which are related to each other and to Egret also showed limited disease with the WA isolates and with certain NSW cultures. Five New South Wales (NSW) isolates produced moderate to severe infection on this cultivar which is field susceptible in NSW. Among the bread wheats used as sources of resistance in southern NSW only one, M1696, remained healthy with all isolates; nine other lines developed little disease with most isolates but more infection with other isolates, especially two isolates isolated from the field in severe epidemics. There was agreement between replicates within and between experiments. The relevance of these findings to breeding programs is discussed.