Blackleg of tobacco

The causative agents of the disease are the fungi Pythium debaryanum and Rhizoctonia solani, whose activity depends on soil temperature: the former pathogen develops primarily at temperatures below 20°C, while the latter develops above this threshold. The disease manifests as thinning and blackening of the base of the seedling stem, resulting in the formation of a characteristic constriction in the root collar zone.

The infection spreads rapidly to the stem and leaf petioles, often accompanied by the appearance of a white or brown fuzzy coating on the surface of the plants and the soil. The process leads to mass wilting of seedlings and the formation of patches of plant death in the seedbed; furthermore, transplanting even slightly affected seedlings into the field results in poor survival and subsequent death.