Management Options - Sheath Blight

Varietal resistance

To date, there is no reliable source of resistance despite the large number of germplasms evaluated. Screening of more than 30,000 lines and varieties at IRRI for sheath blight resistance revealed that not a single variety is totally resistant to disease, but many showed moderate resistance. Tests of related wild rices have failed to provide sources of higher levels of resistance than those found in cultivated species.

In the late 1990s, much effort was exerted on the development of alternative approaches to manage the disease. Approaches included introducing genes that encode protein conferring antifungal activity into different cultivars to enhance tolerance to R. solani. These proteins are normally produced by plants in response to fungal infections. At IRRI, transgenic rice plants with these protein genes, specifically chitinase and thaumatin-like protein, were developed and are at different stages of evaluation. In China, an indica variety was transformed with a rice chitinase gene. Chitinase breaks down the fungal chitin and enhances the level of protection against the pathogen.

Cultural practices

As in the case of blast, the application of nitrogen--based on the actual requirements of the crop--is necessary to manage sheath blight without reducing yield. Sanitation, specifically removing weeds, can help control sheath blight considering that R. solani also attacks weeds that are commonly found in rice fields. Seeding rate may be reduced to have less dense plants. This will help to avoide closer plant spacing that favors the horizontal spread of the disease.

Biological control

Fungal antagonists, such as Trichoderma harzianum and T. viride, and bacterial antagonists, such as Bacillus subtilis, B. cereus, and Pseudomonas fluorescens are being considered as potential biological control agents against sheath blight. Non-pathogenic Rhizoctonia-like fungi were found in rice fields in the Philippines and are also being investigated as potential biocontrol agents.

Chemical control

Control of rice sheath blight has been mainly through the use of foliar fungicides. Several antibiotics and chemicals were tested and found effective against sheath blight. Some of the effective fungicides are benomyl, thiophanate methyl, propiconazole, edifenphos, iprodione and more recently, azoxystrobin. In Japan, Vietnam, Thailand, and Korea, validamycin was found to be an effective curative control against sheath blight. Used in China, jinggamycin is a synonym of validamycin.