Efficacy of Indigenous Antagonistic Fungi against Root-Knot Nematodes on Tomato in Kirinyaga County, Kenya

Abstract

Root-knot nematodes the Meloidogyne species are a serious threat to tomato production in both small and large scale tomato farms in Kenya. Management of the nematode is primarily dependent on the application of chemical nematicides. Chemical nematicides though very effective are expensive and also environmentally unfriendly due to their residual toxicity and pollution of the environment. The main aim of the current study was to improve tomato production through management of root-knot nematodes (RKN) using bio-control agents in Kirinyaga County, Kenya. The efficacy of antagonistic fungi in controlling RKN on tomatoes was evaluated in vitro and in vivo. Tomato root samples were obtained from Mwea. Fungal isolates were isolated from healthy tomato roots and Meloidogyne egg masses by direct plating technique. Root-knot nematodes inoculum was extracted by root maceration method from heavily galled tomato roots. A greenhouse experiment was set up in Kenyatta University and arranged in a Completely Randomized Design (CRD) with 4 replicates. A field with high nematode infestation was identified through soil sampling and analysis for presence of nematodes. The field trials were laid in a Randomized Complete Block Design (RCBD) with 4 replicates. The parameters evaluated included plant height, plant dry weight (roots and shoots), RKN egg hatch rate, juvenile mortality, juveniles’ population in the soil, galling and egg mass indices, reproductive factor and fruit yield of tomatoes. Data collected was subjected to Analysis of Variance (ANOVA) using SAS software version 9.2 and means separated using Fisher’s Least Significant Difference (LSD) test at 5% level of significance. A total of 45 fungal isolates (from roots and RKN egg masses) were identified and placed in various genera including Trichoderma spp., Paecilomyces spp. and Fusarium spp. using morphological characteristics and molecular techniques. Trichoderma spp. was the most prevalent (38%). All the isolated fungi had significant (P≤0.05) effect on egg hatch rate and juvenile mortality in vitro. The RKN egg hatch rate inhibition by the fungal isolates was notably (P≤0.05) higher than in the untreated control. Trichoderma harzianum 2 recorded the lowest egg hatch rate (22.33%) while the highest was in the untreated control (69.33%). The fungal isolates also caused RKN juvenile mortality that was significantly higher than in the untreated control. The highest juvenile mortality (91%) was caused by T. harzianum 2 after 10 days of exposure which was statistically (P≤0.05) greater than the untreated control (2%). The five selected fungal isolates tested in vivo significantly enhanced the growth and yield of tomato as well as reduced the RKN population and reproduction in the soil as compared to the untreated control. Among the tested isolates, Trichoderma harzianum 1 and T. harzianum 2 were the most effective in promoting growth in terms of increased shoot height, root length, plant dry weights and yield of tomatoes. The results of this study show that diverse fungi associated with tomato roots and RKN egg masses have potential of controlling RKN in vitro and in vivo as well as enhance growth and yield of tomato.