Bean botryodiplodia

Systematic position and pathogen nature: Botryodiplodia phaseoli is a fungal pathogen belonging to the Coelomycetes class. It is recognized as a facultative parasite that can alternate between saprotrophic growth on decaying plant matter and parasitic infection of healthy host tissues. Its ability to persist in the soil for several seasons makes it a challenging pathogen for integrated pest management.

Host plants and associated diseases: This fungus primarily affects leguminous crops, with common beans, soybeans, and cowpeas being the most susceptible. The pathogen is responsible for various manifestations of dry rot, including stem blight, root rot, and seed decay. In severe cases, the entire vascular system of the plant can be compromised, leading to rapid wilting and necrosis of the stems.

Biology and life cycle: The pathogen survives during the winter as mycelium and pycnidia within crop residues or contaminated seeds. During the growing season, pycnidia produce massive amounts of conidia, which are disseminated by rain splash, wind, and agricultural equipment. Infection occurs primarily through mechanical wounds or natural plant openings, after which the mycelium penetrates deep into the tissues.

Developmental factors and impact: The disease development is highly favored by high ambient temperatures (between 25°C and 30°C) and high soil moisture. The economic impact of the pathogen is significant, often resulting in severe reductions in stand density, poor pod filling, and compromised seed quality. In many cases, infected seeds may appear discolored, showing dark pycnidial spots on the seed coat.

Control and protection strategies: Managing this disease requires a proactive and multi-faceted approach to minimize inoculum pressure:

• Utilizing high-quality certified seeds treated with broad-spectrum fungicides.
• Implementing long crop rotation cycles, avoiding the planting of susceptible legumes in fields with high previous infestation.
• Promoting the rapid decomposition of plant debris through deep plowing or the use of microbial additives.
• Monitoring fields during critical growth stages and applying foliar fungicides if environmental conditions favor the spread of the pathogen.