Investigating the virulence of isolates produced by sexual recombination between different Pyrenophora teres isolates

Investigating the virulence of isolates produced by sexual recombination between different Pyrenophora teres isolates

Net blotch caused by Pyrenophora teres is a major barley (Hordeum vulgare) leaf disease in Australia resulting in potential losses of up to 40% to the barley grains industry. It is estimated that this disease costs Australian agriculture $60 million a year. Pyrenophora teres occurs as two forms, namely those having net-like symptoms referred to as Pyrenophora teres f. teres (Ptt) and others having spot-like symptoms referred to as Pyrenophora teres f. maculata (Ptm). Progeny have been successfully produced from crossing these two forms in the laboratory and hybrids have also been collected from barley fields. To date the potential evolution of new virulences from crosses between different isolates of the same form and between crosses of isolates of the two different forms has not been investigated. The aim of this study is to a) evaluate a new method (DLA – spray method) for phenotyping net blotch, b) identify the virulences in artificially produced Ptt x Ptt and Ptt x Ptm crosses and c) to fine-map the QTL region containing virulence genes in one of these crosses. To achieve this, different virulence assays were trialled and compared to determine which method is the most suitable and reliable. These trials indicated that the DLA – spray method is a reliable and accurate novel method that can replace both the seedling assay and DLA – droplet method for phenotyping net blotch of barley. Virulences were determined in three existing Ptt x Ptm crosses and one Ptt x Ptt cross by screening ascospores across a differential set of eight barley varieties. Results indicated that the progeny of these populations express virulences different to their parents’. A genetic map had been developed for Ptt x Ptt population NB29/NB85 and phenotypic data used to map the virulence genes in this population. For this study a SSR marker was added to this QTL region. Improved knowledge concerning the occurrence of recombination and the potential for new virulences to be produced can be used to better manage disease incursions and to implement control through deployment of resistances.