Temporal analysis of Grapevine Powdery Mildew Epidemics Progress in Sistan Region, Iran

Grape powdery mildew (GPM) caused by plant pathogenic fungus Erysiphe necator, is the most widespread disease on grapevine in worldwide including Iran. Temporal analysis of disease epidemics was carried out by evaluating GPM in 30 vineyards in three cities of Sistan region, includeing Zabol, Zahak and Hamoon during 2017 and 2018. Field survey of vineyards to record disease incidence (I) and severity (S) was started from plant growth onset to harvest time, weekly program. Disease progress curves (DPCs) were evaluated by mathematical growth models including Linear, Monomolecular, Logistic, Log-logistic and Gompertz and their goodness of fit determined based on such statistics as coefficient of determination (R2), adjusted R2 (aR2)and standard error of estimates (SEE). Result showed that in total two years, for three variables of disease including: disease incidence, leaf disease severity and fruit disease severity, the Monomolecular model was fitted with 100, 100 and 98.33% of studied epidemics respectively. Means R2 of this model for three disease variables, calculated 91.64%, 89.60% and 90.27% respectively and this model was selected as the most appropriate model for describe GPM progress in Sistan region for two studied years.Also in total of two years rates of increase (rm) per unit of disease in the vineyards for three disease variables were 0.016, 0.004 and 0.005 respectively. This research is conducted for the first time in the region of Sistan and Iran.