Rice stem rot

Magnaporthe salvinii (asexual stage Sclerotium oryzae) is an ascomycete fungus that acts as a serious plant pathogen. It is recognized primarily as the causal agent of rice stem rot, a disease that threatens rice production globally, especially in warm, humid climates.

The disease symptoms typically appear on the leaf sheaths near the waterline as small, dark, and irregular spots. As the infection progresses, the fungus penetrates the inner stem tissue, causing it to rot and lose structural integrity. This leads to the characteristic lodging of the rice plants and significant grain shriveling.

The biology of this fungus is centered on its survival structures, known as sclerotia. These black, hard bodies can survive in soil and rice stubble for several years. When fields are flooded for rice cultivation, the sclerotia float to the surface, where they attach to the stems of the rice plants and initiate primary infection through the invasion of the epidermal tissues.

Environmental conditions play a critical role in the severity of an outbreak. Warm temperatures ranging from 25°C to 30°C combined with high humidity create an ideal microclimate for the fungus to multiply. Excess application of nitrogenous fertilizers, which promotes rapid succulent growth, further increases the susceptibility of the crop to infection.

Effective management and control strategies focus on minimizing inoculum levels and improving plant health. Key practices include:

• Removal or burning of crop residues to reduce the number of sclerotia in the soil.
• Strategic water management, such as periodic drainage of the fields to disrupt the infection cycle.
• Balanced fertilization to avoid nitrogen excess.
• Application of targeted fungicides during the active growth stages if disease pressure is high.