Effect of Trichoderma asperellum on growth of Rhizobium leguminosarum in vitro

Trichoderma asperellum has been fronted as a biocontrol agent of root-knot nematodes on tomato and French beans in Kenya. Research on the effect of T. asperellum on growth of Rhizobium species is lacking yet the two interact within the rhizosphere particularly when T. asperellum is applied as a biocontrol agent. Legume roots and Rhizobium species have symbiotic relationship resulting in biological nitrogen fixation. The plant supplies carbon for the energy-dependent reduction of nitrogen and protects the oxygen-sensitive nitrogenase enzyme. Nitrogen is an important primary nutrient element in plant physiology and is a key factor in agricultural production. Trichoderma spp. is increasingly being used as a biological control agent against soil-borne pathogens. The type of interaction between Trichoderma spp. and Rhizobium spp. could affect nodulation and the symbiotic nitrogen fixation process. In this study, the type of interaction between Trichoderma spp. and Rhizobium spp. was established by culturing them on yeast extract mannitol agar (YEMA) which was found to support the growth of both organisms. The effect of T. asperellum on growth of Rhizobium spp. was evaluated by dual culture technique. The means for the radial growth of Rhizobium spp. in presence of T. asperellum were highly significant ( p=0.00). The growth on day 3 was the highest with a mean growth of 29.93 mm followed by the growth on day 5 with a mean of 16.53 mm. There was no rhizobial growth visible on day 7. The in vitro research output indicated that T. asperellum inhibited the growth of Rhizobium spp. by 49.7 to 100 % between day 3 and day 7. The results of this study point towards an antogonistic effect of the biocontrol agent T. asperellem on the beneficial Rhizobium spp and should be further investigated.