Determining the presence of host specific toxin genes, ToxA and ToxB, in New Zealand Pyrenophora tritici-repentis isolates, and susceptibility of wheat cultivars

Abstract

Tan spot, caused by Pyrenophora tritici-repentis (Ptr), is an important disease of wheat worldwide, and an emerging issue in New Zealand. The pathogen produces host-specific toxins which interact with the wheat host sensitivity loci. Identification of the prevalence of the toxin encoding genes in the local population, and the susceptibility of commonly grown wheat cultivars to Ptr will aid selection of wheat cultivars to reduce disease risk. Twelve single spore isolates collected from wheat-growing areas of the South Island of New Zealand representing the P. tritici-repentis population were characterised for the Ptr ToxA and ToxB genes, ToxA and ToxB, respectively, using two gene specific primers. The susceptibility of 10 wheat cultivars to P. tritici-repentis was determined in a glasshouse experiment by inoculating young plants with a mixed-isolate spore inoculum. All 12 New Zealand P. tritici-repentis isolates were positive for the ToxA gene but none were positive for the ToxB gene. Tan spot lesions developed on all inoculated 10 wheat cultivars, with cultivars ‘Empress’ and ‘Duchess’ being the least susceptible and ‘Discovery’, ‘Reliance’ and ‘Saracen’ the most susceptible cultivars to infection by the mixed-isolate spore inoculum used. The results indicated that the cultivars ‘Empress’ and ‘Duchess’ may possess a level of tolerance to P. tritici-repentis and would, therefore, be recommended for cultivation in regions with high tan spot incidence.