Reduction of inoculum of Rhizoctonia solani in soil by germlings of Trichoderma hamatum

Abstract

Three- and 8-day-old inoculum of Trichoderma hamatum (TRI-4), consisting of young, actively-growing hyphae on bran, reduced survival of Rhizoctonia solani in infested beet seed by about 90% during the first week of incubation and prevented growth of the pathogen from beet seed into soil. The 3-day-old inoculum is considered a germling preparation. An older preparation (40-day-old), which did not contain growing hyphae, or conidia on bran (0-day-old) did not reduce survival or growth of R. solani even after 3 weeks of incubation. A 15-day-old preparation reduced survival about 50%. Addition of germlings to soil at a rate of 0.13% reduced pathogen survival and growth as effectively as a 1% rate after 3–6 weeks of incubation. There was nearly complete reduction (>90%) in survival when germlings were added to soil at the same time as seed infested with R. solani or 1 week later; a 50% reduction in survival when added 2 or 4 weeks after R. solani, and no reduction when added to soil 1, 2 or 4 weeks before the pathogen. Saprophytic growth was generally prevented by germlings except if they were added 2 or 4 weeks before the infested beet seed. Isolate TRI-4 rapidly grew from the bran into soil and within 2 days it penetrated and attacked R. solani embedded in beet seed so that pathogen survival dropped to about 20% and the population of TRI-4 proliferated within the seed. Germlings of TRI-4 reduced survival (>90%) and growth (>50%) of several isolates of R. solani in a loamy sand. Survival and growth of R. solani isolate R-23, was reduced more than 90% in seven different soil types within 1 week of incubation. Germlings reduced pathogen survival under all conditions of temperature, moisture and pH studied except under high moisture at 32°C. The greatest reduction (91–100%) was observed at all soil moisture levels at 15° and 23°C and at pH 5.0 and 6.4.