Genetic and pathogenic diversity in Pyrenophora teres f. maculata in barley crops of Victoria, Australia

Forty-four Pyrenophora teres f. maculata isolates collected from barley crops in Victoria, Australia, were used in an analysis of genetic and pathogenic diversity. Genetic analysis with molecular markers revealed high levels of diversity. Fifteen sequence-tagged microsatellite primers revealed polymorphism among the 44 isolates, with two to five alleles (average 2.87 ± 0.42) amplified at each locus. Each isolate exhibited a unique genotype, which was likely to be the result of sexual recombination by random mating in the Victorian pathogen population. The two mating types of P. teres f. maculata were found at almost a 1 : 1 ratio in the 44 isolate set indicating that sexual recombination is possible. Consistent with international studies of this pathogen, the high genetic diversity detected did not correlate with pathogenic variation. A differential set developed in Australia that consisted of 21 barley varieties was evaluated for reaction response towards the 44 P. teres f. maculata isolates as seedlings. None of the isolates tested were virulent on barley varieties known to possess the Rpt4 gene for seedling resistance, or the Ha4 allele associated with adult plant resistance. This indicates that use of the Rpt4 gene, Ha4 allele and other sources of resistance will provide effective control of spot form of net blotch (caused by P. teres f. maculata ) in Victoria. However, the high level of genetic diversity indicates significant potential for the pathogen population to evolve rapidly to adapt to changes in selective pressures such as the deployment of host resistance.