The patho gens are highly effective soil inhabitants capable of colonizing residues easily. All species overwinter as oospores. Reduced soil moisture decreases oxygen tension an d induces exudation of organic materials by seeds, stimulating colonization by Pythium sp. Symptoms of Rhizoctonia infection in seedl ings are evidenced as sunken brownish, red lesions on lower stems at or below the soil line. Taproot cortical tissue is well-decayed and appears reddish brown.
Extensive root rot leads to seedling mortality.
R. solani is part of a whole complex of soilborne fungi which can be recovered from soybean roots, including P. sojae , Pythium sp., and Fusarium sp. The pathogen is an extremely well-adapted soil fungus capable of colonizing debris, growing in soil, and overwintering as mycelium in soil. Rhizoctonia mycelia are identified by ri ght-angle branching of hyphae. Most damage to soybeans results from infection by AG-4. Conditions which promote continued wet soils promote Rhizoctonia damage.