Sheath blight reduces stem breaking resistance and increases lodging susceptibility of rice plants

Sheath blight caused by Rhizoctonia solani (Kühn) and lodging are the most important constraints to achieve high grain yield in intensive and high-input rice production systems. Previous studies have focused on either sheath blight or lodging in its damage to rice crop. The relationship between sheath blight infestation and lodging resistance is still unclear. The objective of this study was to determine the direct effect of sheath blight intensity on lodging-related traits and lodging index. Field experiments were conducted in both early and late seasons in 2009 and 2010 in Wuxue County, Hubei Province, China. The effects of nitrogen (N) rate, hill density, silicon application, fungicide treatment, and inoculation with R. solani on sheath blight intensity and lodging-related traits were investigated. Lodging-related traits and lodging index were determined on the third internode from the top of the plants. In general, sheath blight intensity and lodging index increased with the increases of N rate and hill density. Correlation analysis revealed that sheath blight intensity was negatively related with breaking resistance and positively related with lodging index. The direct effect of sheath blight infestation on lodging resistance was found by using fungicide treatment and inoculation of R. solani. Fungicide treatment increased breaking resistance through reducing sheath blight intensity whereas inoculation decreased breaking resistance through increasing sheath blight intensity. These results suggest that sheath blight reduced the breaking resistance of lower internodes and consequently resulted in poor lodging resistance.

► Sheath blight and lodging increased with the increases of N rate and hill density.
► Sheath blight index was negatively correlated with breaking resistance.
► Sheath blight index was positively correlated with lodging index.
► Direct effect of sheath blight on lodging was confirmed with fungicide treatment and pathogen inoculation.
► Sheath blight reduced breaking resistance and consequently increased lodging susceptibility.