Disease Progress Curves of Sclerotinia Stem Rot of Canola Epidemics in Golestan Province, Iran

Sclerotinia Stem Rot (SSR), caused by Sclerotinia sclerotiorum, is believed as the most important disease of canola (Brassica napus) in Iran. Temporal analysis of the disease epidemics was carried out by evaluating SSR in 80 fields in four locations of: Gorgan, AliAbad, Kalaleh and Gonbad in Golestan Province during 2006 and 2007. Scouting of the fields to record disease incidence (I) and disease severity (S) was started before the end of flowering and continued weekly up to harvest time. Disease Progress Curves (DPCs) were studied using mathematical growth models and their goodness of fit determined based on such statistics as coefficient of determination (R2), standard error of estimates (SEE) and residual plots. Gompertz model with a mean R2 of 94.69% was selected as the most appropriate model for describing SSR progress in field conditions of Golestan Province. Rates of increase (rG) per unit of disease in the canola fields were 0.003 to 0.077 (with an average of 0.03). This is the first temporal study of canola SSR in Iran.