Effect Of Using Trichoderma Asperellum A Biocontrol Agent Aganist Root Knot Nematodes On Nodulation, Galling And Growth Parameters Of French Beans In Kenya

ABSRACT Trichoderma species have been widely reported worldwide as biocontrol agents of plant pathogens and growth promoters. Trichoderma asperellum has been fronted as a biocontrol agent of root-knot nematodes on tomato and French beans in Kenya. However research on the effect of T. asperellum on nodulation particularly in French beans is still lacking. Therefore there is a need to determine the effect of Trichoderma spp. on nodulation. A negative effect could counter the positive effect since Rhizobium species is very important for nitrogen fixation. The objective of this study was therefore to determine the effect of T. asperellum on nodulation in French beans. A total of five treatments were applied. These were T. asperellum at low rate, at medium rate, and at high rate. The other treatments were a standard biological nematicide, Bionematon and an untreated control. Greenhouse experiments were carried out to assess nodulation under controlled conditions. Nodulation index was determined using the nodule size, color, nodule number and nodule biomass. The biomass of the roots and shoots were also assessed as well as root collar diameter. The presence of root-knot nematodes (RKN) within the treatments was confirmed using the Baermann‟s method in the soil and the presence of galls in the roots. Data was analyzed using analysis of variance (ANOVA) and the means were separated using Tukey‟s test at 5 % level. The in vitro research output based on the laboratory experiments indicates that T. asperellum inhibits the growth of Rhizobium spp. by between 50.13 - 100 %. Greenhouse experiments showed that treatment with T. asperellum reduced the galling in French beans significantly and had no effect on the investigated plant growth parameters. There was a significant difference in the nodule number but no significant difference in the nodule biomass. This is probably due to the fact that, although the nodules increased in numbers in the control and in low level of Trichoderma, the nodule size reduced as a result of the high level of galling that occurred in absence of nematode control. In the light of these findings, there is need to evaluate the effect of Trichoderma spp. on nodulation of other legumes and on the growth of other Rhizobium spp. Since nodulation in French beans was reduced by application of T. asperellum, there is need to determine if nitrogen fixation is compromised and whether there in need to revise the amounts of nitrogenous fertilizers applied where the soil is treated with Trichoderma.