Interactions between Rhizoctonia tuliparum sclerotia and soil microorganisms

Abstract

Air-dried sclerotia of Rhizoctonia tuliparum were readily invaded by a number of soil fungi, particularly Mucor, Fusarium and Trichoderma species. Invasion was associated with an apparent rapid loss in viability as measured by germination on agar. However sclerotia were able to infect tulip bulbs, suggesting that germination on agar may not be a good measure of viability in the presence of fungal invaders. Non-air-dried sclerotia from culture were still viable after 2 years when buried in field soil but on the soil surface sclerotia were invaded by fungi resulting in a loss in viability. Some sclerotia (usually < 20%) recovered from infected bulbs were also invaded by fungi. When immersed in water air-dried sclerotia lost more than 60% of their dry weight through leakage. Infectivity of sclerotia dropped after one leakage cycle and viability after two. Materials which leaked from sclerotia included a previously undescribed broad spectrum antibacterial pyrone antibiotic. Soil bacterial populations increased rapidly when air-dried sclerotia were buried in soil. Dead non-antibiotic sclerotia persisted for at least 2 years in soil suggesting that the composition of the sclerotial cell wall may be important in survival.