Rice necrosis

Rice necrosis is a viral disease caused by the Rice necrosis mosaic virus (RNMV), a member of the Potyviridae family, genus Bymovirus. This phytopathogen specifically targets rice crops, posing a risk to yield stability and quality in endemic regions. It is characterized by its reliance on specific biological vectors present in the soil environment.

The disease manifests through distinct symptoms on the leaves, including chlorotic streaking and necrosis of the leaf blades. As the infection progresses, the viral accumulation impairs the photosynthetic capability of the plant. This physiological stress leads to stunted growth, reduced tillering, and poor grain development, which directly impacts the economic output of the field.

The biology of RNMV is inextricably linked to the fungal vector Polymyxa graminis. This soil-borne fungus acts as the primary reservoir and transmitter of the virus. The virus persists in the resting spores (cystosori) of the fungus within the soil for several years, making the elimination of the source of infection extremely difficult once the field is infested.

Environmental conditions play a critical role in the dissemination of the virus. High soil moisture, typical of irrigated rice cultivation, stimulates the release of zoospores from the fungus. These zoospores actively migrate through the water film in the soil to locate and penetrate the roots of the rice plants, effectively inoculating the crop with the virus.

Effective management and control measures involve several agronomic strategies:

• Selection of resistant or tolerant rice varieties through breeding programs.
• Implementation of long-term crop rotation to exhaust the soil-borne fungal population.
• Enhancement of soil drainage systems where applicable to reduce moisture-dependent vector activity.
• Rigorous sanitation practices to prevent the movement of contaminated soil between different plots.