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Effect of temperature on aggressiveness of newly discovered fsp of the grape downy mildew pathogen Plasmopara viticola fsp riparia and fsp aestivalis

Romaric Armel Mouafo Tchinda: Sherbrooke University

<div>Grape downy mildew, caused by the oomycete <em>Plasmopara viticola</em>, is among the most important grapevine diseases worldwide. In recent studies, two different cryptic species of <em>P. viticola</em> were found in eastern Canada: <em>P. viticola </em>f.sp<em>. riparia</em> and f.sp. <em>aestivalis</em>. But, their epidemiology, ecology and significance for management purposes are unknown. This research aims at studying the influence of temperature on zoospores release and aggressiveness of the two newly discovered <em>formae spacialis</em>. The temporal dynamic of zoospore release, infection and sporulation was evaluated on grape leaf disks at six temperatures (5 to 30<sup>o</sup> C, 5<sup>o</sup> C increments). For both genotypes, the highest zoospore release was observed after six hours at temperature ranging from 15 to 20<sup>o</sup>C, but there was no significant difference between genotypes, except at 25<sup>o</sup> C where <em>P.v. aestivalis</em> showed more empty sporangia than <em>P.v riparia</em>. The two genotypes germinated at all tested temperatures except at 30<sup>o</sup> C. Both genotypes were able to infect at temperature ranging from 15 to 25<sup>o</sup> C and sporulated at temperature ranging from 10 to 25<sup>o</sup> C. However, according to the least square mean analysis, combining infection efficiency, disease incidence, sporulation and latency,<em> P.v. aestivalis</em> was significantly more aggressive than <em>P.v riparia</em> (temperature range between 15 to 25<sup>o</sup> C). The knowledge gained during this project will be used to adapt downy mildew management tools and to improve disease management strategies.</div>