Evaluation of antagonistic plants for root-knot nematode (meloidoygyne spp.) management in tomato
Tomato is attacked by several plant parasitic nematodes but root-knot nematodes are the most important causing considerable losses. Studies were undertaken in the greenhouse to determine the suppressiveness of a wide range of plant species to root knot (Me/oidogyne spp.) nematodes. Plants were grown in pots and inoculated with 6000 eggs and lor juveniles. The treatments were arranged in a completely randomized design with 10 replications. After sixty days, the experiment was terminated and galling, egg mass indices and juvenile counts determined on a scale of 1-9 and the modified Baermann funnel technique, respectively. A field experiment was conducted to verify the greenhouse results in nematode infested microplots. This was arranged in a randomized complete block design with three replications. After three months the experiment was terminated and similar data taken. Among the plants tested, Tagetes patu/a, Gossypium hirsutum, Desmodium unicinetum, Chloris gayana, Zea mays, A/strameria sp., Capscium allium, Crata/aria juncea, Arachis hypogaea, Sorghum bicoior, Tithonie diversiflora and Pennisetum purpureum were rated as suppressive with galling and egg mass indices ranging from 0-3. High galling and egg mass indices of 7.0- 9.0 were recorded on Allium cepa, Statice sp., Brassica o/eracea var. capitata, Helianthus annuus, Lab/ab purpure us, Coriandum sativum and Vigna subterranea while the rest of the other plants were rated moderately resistant with galling and egg mass indices ranging from 3.0-6.1. Results of an experiment conducted in the greenhouse to determine the level of root penetration of resistant plants by Me/oidogyne juveniles showed that penetration was lower in some plants. Penetration was 95% lower in T. patu/a and 80% lower in crotalaria as compared to the control (tomato). Damage by nematodes was significantly (P!:. 0.05) reduced in tomato plants planted following a crop of sweetcorn alone or in combination with Tagetes patu/a, Grata/aria juncea, sorghum bicotor and Asparagus sp. in the field. After the first season, nematode population density continued to decrease in all the treatments while it continued to increase throughout the two seasons under tomato monoculture. Tomato plants grown in association with Tagetes patu/a, rhodes grass and sweetcorn had lower galling indices of not more than 1.5 compared to associations with cotton, crotalaria, sorghum, asparagus, garlic, chrysanthemum, tithonia, spring onion and sesame where gall indices were higher than 2.0. This study shows that despite the wide host range of Me/oidogyne species, there is a wide range of economically important plants from which suitable candidate crops can be chosen and incorporated into different cropping systems. Some of the plants can be grown for advantages of soil fertility improvement through nitrogen fixization, to prevent soil erosion, quality forage and ornamental value. Extensive on-farm studies in different agroecological zones needs to be carried out and the mechanisms of nematode suppression established.