Vegetable plant vigor and suppression of Meloidogyne incognita with vetiver shoot amendments in soil

Authors: JINDAPUNNAPAT, KANSIREE - Kasetsart University; Meyer, Susan; Macdonald, Margaret; Reetz, Nathan; Chitwood, David; Masler, Edward; SOONTHORNCHAREONNON, NOPPAMAS - Mahidol University; Camp, Mary; SASNARUKKIT, ANONGNUCH - Kasetsart University; CHINNASRI, BUNCHA - Kasetsart University

Submitted to: Nematropica
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/24/2019
Publication Date: 1/29/2020
Citation: Jindapunnapat, K., Meyer, S.L., Macdonald, M.H., Reetz, N.D., Chitwood, D.J., Masler, E.P., Soonthornchareonnon, N., Camp, M.J., Sasnarukkit, A., Chinnasri, B. 2019. Vegetable plant vigor and suppression of Meloidogyne incognita with vetiver shoot amendments in soil. Nematropica. 49:208-219.

Interpretive Summary: Plant-parasitic nematodes are microscopic worms that attack plants and cause U.S. crop losses of ten billion dollars each year. Root-knot nematode has a wide range of plant hosts, and management of this nematode is a significant agricultural problem. Therefore, vetiver grass was studied by a team from ARS and Thailand to determine its usefulness for suppressing populations of this nematode. Vetiver grass is widely planted for many purposes, including essential oil production and prevention of soil erosion. This grass also produces shoots that can be chopped and amended into soil to increase growth of crop plants. Because some vetiver grass cultivars are resistant to certain nematodes, the commercially available cultivar Sierra was tested and found to be resistant to southern root-knot nematode. Greenhouse studies with cucumber, pepper and tomato seedlings transplanted into soil that had been amended with chopped vetiver shoots showed that effects on vegetable plant growth were variable. Tomato seedlings had smaller shoots and roots in higher vetiver amendment rates, but cucumber plant growth was not always affected by the vetiver amendment. It was also shown that vetiver grass amended into soil could reduce densities of nematode eggs produced on cucumber roots. These results are significant because they demonstrated that planting vetiver grass, and amending the shoots into soil, may be useful as part of a strategy for managing root-knot nematodes. This work will be used by researchers developing safe, plant-derived sources for reducing crop losses caused by nematodes.

Technical Abstract: Vetiver grass (Vetiveria zizanioides (L.) Nash) 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). A commercially available vetiver cultivar (Sierra) was therefore tested for host status to Meloidogyne incognita (Kofoid & White) Chitwood, 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. 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, and 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 weeks after vetiver amendment, as opposed to transplanting sooner after amendment application. Vetiver soil amendments were also tested in the greenhouse for suppression of M. incognita on cucumber at 1%, 3%, 5% and 10% fresh vetiver/g soil (weight/weight). Only the highest amendment rate consistently suppressed nematodes on cucumber roots; numbers of eggs/g root were 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.