Effect of Trichoderma harzianum biomass and Bradyrhizobium sp. strain NC 92 to control leaf blight disease of bambara groundnut (Vigna subterranea) caused by Rhizoctonia solani in the field

Four hundred and sixty two strains of Trichoderma spp. were isolated from 23 soil samples in which groundnut (Arachis hypogaea L.) and bambara groundnut (Vigna subterranea L.) had been planted in Songkhla, Phattalung, Nakhon Si Thammarat, Narathiwat and Yala provinces. These fungi were tested against Rhizoctonia solani, a causal agent of leaf blight of bambara groundnut, using dual culture technique on PDA medium. Among 462 isolates tested, 226 isolates had an ability to overgrow R. solani completely. Further testing found 13 isolates having the ability to parasitize mycelia of R. solani. Among these isolates, ThB-1-54 produced a cellulolytic enzyme on congo-red agar. This isolate was later identified as T. harzianum Rifai. In the field test, applying biomass of the isolate ThB-1-54 cultured on ground mesocarp fiber of oil palm, the combination of the isolate ThB-1-54 on ground mesocarp fiber of oil palm and Bradyrhizobium sp. (strain NC 92), or fungicide (iprodione) had no effect on disease severity, yield, or the amount of total nitrogen content in stems or seeds of bambara groundnut plant