Differences in zoospore germination and host penetration in response to temperature among Western Australian isolates of Plasmopara viticola
M. G. Williams A C , P. A. Magarey B and K. Sivasithamparam AA Plant Pathology Group, Soil Science Discipline, Faculty of Natural and Agricultural Sciences, School of Earth and Geographical Sciences, The University of Western Australia, 35 Stirling Hwy, Crawley, WA 6009, Australia.
B South Australian Research and Development Institute, GPO Box 411, Loxton, SA 5333, Australia.
C Corresponding author. Email: mia.williams@curtin.edu.au
Australian Journal of Agricultural Research 58(7) 702-710 https://doi.org/10.1071/AR06274
Submitted: 22 August 2006 Accepted: 26 March 2007 Published: 26 July 2007
Abstract
Plasmopara viticola, causal agent of grape downy mildew, was first detected in Western Australia (WA) in widespread commercial viticulture in the Swan Valley (–31.85 S, 116.02 E) in 1998. It has since been found in all viticultural areas in WA, which extend from the far north (–15.75 S, 128.74 E) to the far south (–35.02 S, 117.80 E) of the state across a diverse range of climate zones. Not all of these zones are considered conducive for the development of grape downy mildew. The early infection behaviour of P. viticola isolates, obtained from climatically different grape-growing locations, was examined under different temperatures of incubation (10, 20, and 30°C). Variation in early infection behaviour was used to discern ecotypes of the pathogen. Ten isolates were obtained from WA and 8 of these responded similarly. Three isolates obtained from the east of Australia and used as comparisons in the study behaved similarly to most of the WA isolates. Zoospore germination and host penetration occurred at 10 and 20°C for all isolates. None of the isolates penetrated the host at 30°C. Only 2 isolates, from WA, germinated at 30°C. The early infection behaviour of most of the P. viticola isolates examined in this study appears to be reasonably analogous, despite the influence of varied local environmental conditions. The capacity of certain isolates to germinate under a wider spectrum of temperatures could be indicative of ecotypic specialisation. Such behaviour could confer advantage for the pathogen in viticultural regions that experience high temperatures throughout the growing season.
Additional keywords: adaptation, evolution, Oomycete, selection, survival.
Acknowledgments
The authors thank Mr Peter Wood and Mr Colin Gordon (Department of Agriculture and Food Western Australia, Perth, WA), Dr Ian Dry (CSIRO, Plant Industry, Adelaide, SA), Dr Michael Fuhlbohm (Department of Primary Industries and Fisheries, Kingaroy, Qld), and Mr Tom Wisdom (Selwyn Viticultural Services, Jindong, WA) for providing samples of grapevine leaves infected with Plasmopara viticola.
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