Understanding genetic variation in grapevine diseases and the genetic basis for pesticide resistance
Grapevine diseases that are caused by fungal/oomycete pathogens such as Botrytis and powdery and downy mildews are responsible for significant crop losses. Current control measures rely on spraying with agrochemicals; however, there is growing evidence for resistance of fungal/oomycete pathogens to specific fungicides. By determining the genetic basis of these resistant phenotypes, DNA diagnostics to efficiently test for potential resistance prior to choosing an agrochemical will be developed and compared to established slow and complicated assays. This will provide impartial data to inform agrochemical purchasing and spray decisions, and potentially guide the development of next-generation agrochemicals.
Investigating fungicide resistance in three pathogens
Powdery mildew (E. necator), Botrytis bunch rot and downy mildew (P. viticola) are the three most economically important diseases in Australian vineyards. To determine the incidence and severity of fungicide resistance in Australia, samples of all three diseases were collected from vineyards in the main viticultural regions of Australia and tested against a range of commonly used fungicides. Representative samples were genotyped for the presence of known mutations conferring resistance. Results showed that resistance to quinone outside inhibitor (QoI) fungicides in powdery mildew was found in most viticultural regions. While phenotypic resistance of E. necator to the demethylation inhibitor group of fungicides was not widespread, the Y136F allele (a known genetic marker in resistant isolates) was present in approximately 60% of the isolates. Populations of P. viticola resistant to metalaxyl have been confirmed in all states except South Australia, and the allele conferring resistance to QoI has been detected. B. cinerea populations resistant to fenhexamid, iprodione, pyrimethanil, boscalid, tebuconazole and azoxystrobin were detected. While 38% of the 114 sites tested had no resistance detected, ten sites had populations resistant to four or more fungicides.
The results so far have confirmed the presence of populations of these three pathogens that are resistant to many fungicides throughout Australia. However, more work is needed to confirm how these results relate to the potential for field failure.