Assessment of Yield Loss Due to Rice Blast Disease in Iran

Grain yield loss in rice (Oryza sativa L.) caused by blast disease, Magnaporthe grisea (Hebert) Barr, is a major concern of rice growers worldwide. Blast is considered as the most injurious disease of rice in Iran, resulting in severe loss especially to susceptible rice cultivars. In order to assess yield loss caused by blast pathogen and develop an appropriate model, different disease onsets and levels were simulated in the experimental field in a split-plot experimental design. Independent variables including early diseased leaf area (X1), final diseased leaf area (X2), early neck blast index (N1), final neck blast index (N2), area under leaf blast disease progress curve (AUDPC1) and area under neck blast disease progress curve (AUDPC2) were taken as predictors and regressed to the loss in yield. Statistics as coefficient of correlation (r), coefficient of determination (R2), adjusted coefficient of determination (aR2), standard error (SE), F and Durbin-Watson were considered in evaluating the resulting models. The most appropriate model was the one which predicts rice yield loss based on final diseased leaf area and final neck blast index.