Optimal conditions for sporangia formation and germination of Plasmopara viticola

Abstract

Downy Mildew is one of the most destructive diseases of grapevines occurring in most grapegrowing areas of the world. It is caused by the obligate oomycete Plasmopara viticola, resulting in the reduction of production due to cluster destruction and the decrease of the wine quality due to fallen foliage. In order to obtain massive viable sporangia of P. viticola for screening biological and chemical control agents, optimal conditions for sporangia formation and germination of P. viticola were studied. The effects of light treatment (24h light/24h dark and 12h light/12h dark), temperature range (15ºC, 20ºC, 25ºC) and nutrient availability (2% lactose, 2% sucrose, or 2% glucose) on sporangia formation and germination were assessed. The percentage of diseased spots compared to total number of spots of the whole leaf inoculated with the same amount of sporangia suspension was calculated under above-mentioned conditions. Results showed that the best conditions for sporangia formation were at 20ºC under dark and 100% humidity, and with 2% lactose supplemented in sporangia suspension. To evaluate optimal conditions for sporangia germination, factors such as temperature stimulation (sporangia suspension treated at normal temperature and 4ºC before inoculation), nutrient availability (2% lactose or sterile distilled water) and illumination period (24 h light/24 h dark and 12 h light/12 h dark) were tested. The germination rate was determined on water agar. Experiments showed that optimal conditions for P. viticola sporangia germination were 2% lactose and stimulation at low temperature for 30 min at dark.