VEGETABLE PLANT VIGOR AND SUPPRESSION OF MELOIDOGYNE INCOGNITA WITH VETIVER SHOOT AMENDMENTS IN SOIL
Vetiver grass (Vetiveria zizanioides) is widely planted in tropical areas, and has many uses, including application of shoots as a mulch or soil amendment. Vetiver produces compounds that are active against nematodes and various cultivars are resistant to Meloidogyne spp. (root-knot nematodes). The commercially available vetiver cv. Sierra was tested for host status to Meloidogyne incognita and found to be resistant. To determine effects of vetiver soil amendments on vegetable crops, we conducted greenhouse trials with seedlings of cucumber, pepper, and tomato transplanted into soil that had been mixed with chopped, fresh vetiver shoots at 0%, 3%, and 5% g fresh vetiver/g dry soil (weight/weight). Results varied with time of amendment, amount of vetiver green manure, and plant species. Cucumber seedling response varied from no significant effect to some phytotoxicity. Tomato seedlings had lower shoot heights and root fresh weights in higher vetiver amendment rates. Pepper roots tended to be smallest when seedlings were transplanted into amended soil 3-4 wk after vetiver amendment, as opposed to transplanting soon after amendment application. Vetiver soil amendments were also tested in the greenhouse for suppression of M. incognita on cucumber at 0%, 1%, 3%, 5%, and 10% g fresh vetiver/g dry soil (weight/weight). Only the highest amendment rate consistently suppressed nematodes on cucumber roots with eggs per gram root reduced by 46% to 67% compared with the controls without vetiver amendment. Further studies would indicate whether amending soil with vetiver at practical application rates, if incorporated as part of a broader strategy for nematode suppression, could potentially contribute to root-knot nematode management.