Castor bean grey mold

The disease is caused by the fungus Amphobotrys ricini, which is a specialized pathogen affecting the castor bean plant. It is classified as a necrotrophic pathogen that triggers severe rot in the reproductive tissues. The fungus completes its life cycle by extracting nutrients from the host, leading to rapid tissue degradation and loss of fruit production.

The primary host for this fungus is the castor bean plant (Ricinus communis). The pathogen specifically targets the inflorescences (racemes) and developing capsules. While it primarily affects the fruiting bodies, in cases of severe infection, it can also manifest on leaves and stems, leading to overall plant decline during the maturation phase.

Symptoms of the infection typically appear as a thick, greyish fungal mat covering the floral parts. As the infection progresses, the tissues turn dark brown or black and become necrotic. The capsules fail to fill properly, often rotting entirely on the plant, which results in significant yield reduction and poor seed quality due to fungal colonization.

The development of Amphobotrys ricini is heavily dependent on microclimatic conditions, specifically high humidity and moderate temperatures. Prolonged rainy weather during the flowering stage is the most critical factor that triggers widespread outbreaks. The spores are primarily dispersed via wind and rain splashes, allowing the pathogen to spread quickly within a field.

To control the disease, integrated management strategies are required. Essential practices include the use of resistant varieties, crop rotation to reduce inoculum in the soil, and proper field sanitation to remove infected plant debris. Additionally, applying chemical fungicides during the peak flowering stage is crucial to prevent the infection from establishing in the inflorescences.