The effect of overwintering sclerotial density on severity of sheath blight disease and rice yield loss

Sheath blight disease of rice caused by Rhizoctonia solani AG-1 IA, has been recognized as one of the most economically important rice diseases in the worldwide. Predicting inoculum density and understanding their survival will lead to agronomic management and reducing the application of fungicides in controlling this disease. The objective of this study was to investigate the effect of overwintering sclerotial density on rate and density of sheat blight disease and rice yield loss in weather conditions of Guilan province, Iran. For this purpose, a field experiment was conducted in a randomized complete block design with three replications in research fields of Rice Research Institute of Iran (RRII), Rasht, Iran, during 2017-2019. Treatments were 0, 12, 24 and 36 sclerotia in a plot of 9 m2, respectively, and the studied variety was the Iranian improved variety, Shiroudi. The results showed that inoculum (sclerotial) density had a significant effect on the development of rice sheat blight and its high density in the field resulted to increased disease and yield loss in rice growth stages. Study on the overwintering sclerotial densities during two years of experiment also showed that the amount of post-harvest rainfall had a significant effect on the survival of sclerotia and reduced them. Therefore, elimination or reduction of primary inoculum and prediction of survival rate of the disease agent under field conditions can be one of the most effective strategies in controlling rice sheath blight disease.