Occurrence of Phytonematodes and Biocontrol of Meloidogyne Spp. (Root-Knot Nematodes) on Tree Tomato (Solanum Betaceum) in Kiambu and Embu Counties, Kenya

Abstract

Tree tomato (Solanum betaceum Cav.) is an important fruit in Kenya whose popularity is growing among farmers and consumers due to its high potential as an income earner and health benefits. Plant parasitic nematodes (PPNs) and especially the root-knot nematodes (RKNs), pose a major threat to its production. This study was conducted to determine, the diversity of PPNs associated with tree tomatoes in Kiambu and Embu counties, Kenya; the responses of six tree tomato varieties to RKN infection and the efficacy of commercial bio-control agents applied singly or in combination against RKNs of tree tomato. Soil and roots from the rhizosphere of 10 plants per farm were collected from 60 farms in the study counties and questionnaires were administered to get more information on the farming practices. Composite samples were processed at the Kenyatta University Nematology Laboratory. Nematodes were extracted and enumerated from 200cm3 of soil and 5g of roots using modified Baermann extraction tray method. In the greenhouse experiments, seedlings were inoculated with 2000 J2s (cultured in a susceptible tomato in vivo) per pot and replicated four times in a completely Randomized Design. Un-inoculated treatments served as control. In the field, experiments were established in a naturally infested field at Kenyatta University and treatments replicated thrice in a Randomized Complete Block Design and BioNematon treatments served as control. Data on plant growth and disease parameters was taken and subjected to Analyses of Variance (ANOVA) using SAS software version 9.1. Means were separated using Tukey’s HSD at P≤0.05. Regression and t-test analysis were done to check for relationships between parameters and significant differences between means respectively. The survey revealed that 98.4% of the farmers intercropped tree tomatoes with other crops while 1.6% did not. All the three PPNs orders: - Tylenchida, Triplonchida and Dorylaimida representing 62.3%, 12.4% and 25.3%, respectively, were isolated from the roots. In soil and roots, Meloidogyne spp. had the highest mean population density of 84.62 and 20.22 nematodes respectively. In addition, Pratylenchus and Helicotylenchus were also among the most dominant genera isolated. Based on the nematode reproduction factor (Rf), Ruby red, Rothamer and Red oratia were moderately resistant both in the greenhouse and in the field. Red light oratia and grafted tree tomato were moderately resistant in the greenhouse but tolerant in the field. Trichoderma asperellum treated plants had significantly higher mean dry shoot weight (DSW) of 13.28g in the greenhouse while plants treated with Bacillus subtilis had significantly higher DSW of 60.58g in the field compared to positive control. T. asperellum and B. subtilis combination significantly reduced nematode Rf with a mean of 0.04 compared to positive control. Farming practices may have contributed to occurrence and distribution of PPNs in the study areas. Moderately resistant and tolerant varieties should be promoted to farmers to manage RKNs in tree tomato. Farmers should also use T. asperellum and B. subtilis formulations to manage RKNs in tree tomato.