Incidence, prevalence and management of root-knot nematodes (meloidogyne spp.) on selected indigenous leafy vegetables in Kisii and Trans-Mara Counties, Kenya

Abstract

Solanum nigrum L., Cleome gynandra L. and Amaranthus spp. are some of the indigenous leafy vegetables (ILVs) that contribute to food diet, income generation, good nutrition and health to resource-poor farmers in Kisii and Trans-Mara counties. The production of ILVs is constrained by inadequate land, diseases and pests of which, root-knot nematodes (RKN) are the most damaging pests to vegetable crops causing about 30 % yield losses globally. However, there is no information about the incidence, prevalence and management of RKN on ILVs in Kenya or worldwide. A survey was conducted in Kisii and Trans-Mara to determine the incidence and prevalence of RKN in ILVs and the available germplasms were screened for response to Meloidogyne spp. in greenhouse. Five organic amendments (OAs) commonly used in the areas of study for ILVs cultivation were also evaluated for their effects on RKN on C. gynandra, S. nigrum, S. villosum and Amaranthus spp. in greehouse and field tests. The amendments included: tea (Camellia sinensis (L.) Kuntze) residues (Tres) and rejects (Trej), decomposed cattle manure (CM), goat manure (GM) and Tithonia diversifolia manure (Td). The amendments were incorporated into the sterilized soil in micro-pots and the field at recommended rates. Unamended soils served as controls. After ninety (90) days, the disease and plant growth parameters were assessed. The study revealed that, 62.8 % of the farms surveyed were infected with RKN. The disease incidence was generally higher in the black nightshades from Kisii compared to those from Trans-Mara, while disease incidence in spider plants and amaranths was generally higher in Trans-Mara compared to Kisii Counties. Black nightshades were susceptible to RKN with green berried recording higher reproduction and galling index compared to susceptible check, while amaranths and spider plants had lower scores «15.0 %) in the screening experiment. All OAs significantly (P<0.05) reduced final populations, rate of galling and reproduction of RKN relative to unamended soil. The reduction in such parameters greatly varied with the type of the OA and the host plant. Generally, Tres and Trej were most effective (P<0.05) against RKN galling followed by Td, while CM and GM were the least. However, corresponding decrease in ILV growth was observed in Tres and Trej amendment while, the other OAs showed significant growth increase under greenhouse conditions. As for managing RKN on ILVs,:Tres and Trej were the most effective inhibitor to its build-up followed by Td manures. Percentage increase in black nightshades and amaranth shoot height and biomass was obtained in soils amended with Td, CM and GM compared to Trej and Tres in pots yet in the field Tres increased plant growth significantly. Further studies are imperative to correctly identify all the prevailing races of Meloidogyne spp. across various soil types in the study areas in addition to determination of the mechanisms of control by the OAs for proper nematode management.