Evaluation of root- knot nematode management strategies based on nematode distribution in tomato (solanum lycopersicum) fields in Mwea, Kirinyaga County, Kenya
Wabere, George Ngundo
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Plant parasitic nematodes (PPN), particularly root-knot nematodes (RKN) are a serious pest problem in smallholder tomato farms in Kenya. For sustainable food production, effective management of plant parasitic nematodes is essential. Root-knot nematode management is primarily dependent on the application of chemical nematicides and the use of resistant varieties. However nematicide application is often done uniformly regardless of the relative nematode distribution in the farms, and yet it is a well-documented fact that plant parasitic nematodes particularly RKN are irregularly distributed due to their reproductive patterns and low mobility. Therefore, identification of specific nematode infested areas within individual fields for targeted RKN management strategies may allow producers to maximize yields, lower production costs and ultimately be less detrimental to the environment. This study evaluated the use of RKN resistant varieties and the application of nematicide under varying nematode densities in Mwea, Kenya. Nematode resistant tomato varieties; Assila, Sandokan and a susceptible variety, Rio-grande in combination with varying applications of a commonly used nematicide Mocap (Ethoprophos) at the rate of 1g, 2g and 4g per plant applied at planting, were evaluated. Areas with 5 to 12 and 32 to 108 RKN per 200 cm3 of soil were chosen to represent low and high RKN densities respectively. The General Linear Model Procedure for univariate analysis of variance analysis was used to test for significant main and interaction effects. The Tukey's HSD (honestly significant difference) test was used to separate the means. From the baseline survey, a total of 12 genera of plant parasitic nematodes were identified The most abundant plant parasitic nematode genera found were the root-knot nematodes (Meloidogyne spp.), followed by the lesion nematodes (Pratylenchus spp.) with a maximum of 110 and 116 nematodes per 200 cm3 of soil, respectively. Mocap application at the recommended rate of 2 g per plant did not significantly (p>0.05) reduce the RKN population and did not eliminate the RKN under both field and greenhouse conditions. In greenhouse experiments, the addition of 4 g of Mocap per plant at planting however was shown to significantly reduce the nematode infestation and ultimately increase yields under high RKN densities with the variety Asilla recording the highest yields of 2,125.7g per plant. The variety Rio Grande recorded the lowest yields of 383.6g per plant under the same conditions. The application of Mocap at the recommended rate of 2gm per plant significantly reduced the numbers of second stage juveniles (J2s) observed at the root zones of sampled plants but did not significantly reduce (p<0.05) the galling index observed on the plants. The variety Assila, combined with the application of 4 gm per plant of Mocap was found to be the most cost effective management strategy for RKN under both high and low RKN densities. According to the findings of this study, it is recommended that farmers intending to plant tomato in the Mwea begin by having their soils tested for the presence of RKN and apply the nematicide Mocap at 4g per plant only on areas where there are either high or low RKN densities. It is also recommended that they plant RKN resistant varieties such as Asilla in such areas. It is is however not economical to apply these measures to areas with no RKN incidences.