Biological management of root and collar rot (Rhizoctonia solani) of Frenchbean (Phaseolus vulgaris)

Abstract

Twelve isolates of Trichoderma were screened in vitro during 2006–08 against Rhizoctonia solani Kuhn. causing root and collar rot of Frenchbean (Phaseolus vulgaris L.) by dual culture tests and production of volatile and nonvolatile antibiotics and it was found that all the isolates significantly inhibited the mycelial growth of R. solani. The isolate ThrAN-5 was most effective in suppression of mycelial growth of test pathogen, followed by TvAN-3, ThrAN- 7, ThrWB-1 and ThrWB-2. ThrAN-5 was most effective in view of percentage inhibition of mycelial growth of R. solani (73.8 and 83.9%) by production of non-volatile substances at variable concentrations (7.5 and 15.0% respectively). Highest per cent germination (91.0%) vigour index (1287.0) and seedling biomass (772.5 mg) of Frenchbean seeds were recorded when the seeds were primed with TvAN-5, followed by ThrAN-5 and ThrWB-1. The bacterial antagonist Ps. fluorescens was also very effective in inducing germination behaviour of Frenchbean seeds. The collar rot of Frenchbean (c.o.-R. solani) was most effectively controlled in greenhouse test by seed and soil application of ThrWB- 1 (79.0%), followed by TvAN-5 and ThrAN-5 (78.2% each), TvAN-3 (77.6%) while the isolate TvAN-10 was the least effective isolate with only 67.4% reduction in disease incidence. The highest germination (%), per cent reduction in disease incidence and increase in green pod yield of Frenchbean was recorded with combination of seed and soil application of ThrWB-1 (348.2%) over control under R. solani sick field condition, followed by T15 (TvAN-5, 345.8%), T6 (ThrAN-5, 343.4%), T12 (TvAN-3, 339.7%) while lowest (239.7%) increase in yield was noted with seed application of TvAN-10 (T16 treatment).