BIOLOGICAL MANAGEMENT OF ROOT KNOT NEMATODES (Meloidogyne spp.) USING AFRICAN LEAFY VEGETABLE, Crotalaria spp.

Abstract

Root knot nematodes are a serious biotic production constraint affecting vegetable production in Kenya. The adoption of sustainable management strategies including the use of antagonistic plants is important in reducing the amount of losses attributed to this soil pest. This study aimed at determining the host suitability of different Crotalaria species against root knot nematodes, assessing different Crotalaria application methods (preplant, aqueous extract and soil amendment) and quantifying nematode infestation at different nematode inoculum threshold levels. A field survey was undertaken in western Kenya to collect root and soil samples as the nematode source. Seven Crotalaria species were screened on pot experiments under green house conditions (23oC). Subsequent in vitro tests were done on extracts under laboratory conditions. Inoculation was done at an equal threshold level of 3000 juveniles while in vitro set up was done at same concentrations (v/v). For the efficacy assessment of the application methods, the most resistant species was applied in two ways under greenhouse. Two vegetables; Solanum nigrum and Cleome gynandra were used during the study. Four different nematode inoculum threshold levels were quantified for the amount of plant infestation. The set ups were arranged in a complete randomized design. Resistance related data based on the reproduction factor (Rf), galling index (GI) and percentage survival of the juveniles, percentage reduction in infestation (galling and nematode population) were then recorded. Data was subjected to analysis of variance and the means separated using Fisher’s protected LSD. There were significant differences in host suitability to the root knot nematodes (P < .001) amongst the seven Crotalaria species tested. The species C. intermedia showed high nematicidal effect and resistance to nematode infestation (low Rf and high galling index) while C. trichotoma was relatively susceptible with a higher Rf value. The aqueous extract application revealed that the different species were significantly different with C. intermedia being the most resistant. Assessment of the two application methods (soil amendment and preplant) indicated that preplant application was a superior method of application as it caused an infestation reduction of 72.13% in root galling and 26.8% in the number of nematodes in the rhizosphere. The different inocula threshold levels showed significant difference in the level of inocula threshold and level of infestation though with a variation in the crop type. The present study’s findings support the use of C. intermedia applied as a preplant and for use at higher than 2000 threshold for Cleome gynandra and at whichever threshold for Solanum nigrum. Key words: