Effect of Wetness Duration and Incubation Temperature on Development of Ascosporic Infections by Sclerotinia sclerotiorum.

Abstract

The impact of wetness duration and incubation temperatures on Sclerotinia sclerotiorum ascospore germination and ascosporic infection efficiency were evaluated. Ascospore germination was optimal when incubated in continuous moisture (free water) at 21°C. Significantly lower germination was observed at 10 or 30°C. Interrupting ascospore wet incubation was detrimental for germination. In infection efficiency studies, dry bean and canola flowers were inoculated with dry ascospores and placed on leaves of dry bean and canola plants, respectively. Dry bean plants were incubated for 196 h at 18 to 20°C in alternating 8 to 16 h wet/12 to 24 h dry periods. Canola plants were incubated for 240 h at 10, 15, 20, 25, or 30°C in alternating 6 to 18 h wet/18 to 6 h dry periods. Interrupting wet incubation delayed symptom appearance and hindered development of the epidemics on both plant types. Logistic regression models estimated at 50% the probability of disease development on dry bean and canola plants when 68 and 48 h of wet incubation at 20°C accumulated in a period of 6 days, respectively. The canola model was validated using data from field trials. Results of these studies will contribute to develop more accurate warning models for diseases caused by S. sclerotiorum.