Suppression of Meloidogyne incognita by extracts and powdered fruits of Gleditsia sinensis (Chinese honeylocust)

Authors: WEN, YANHUA - South China Agricultural University; Chitwood, David; Vinyard, Bryan; WEI, BAI - South China Agricultural University; Meyer, Susan

Submitted to: Nematropica
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/22/2017
Publication Date: 3/5/2018
Citation: Wen, Y., Chitwood, D.J., Vinyard, B.T., Wei, B., Meyer, S.L.F. 2017. Suppression of Meloidogyne incognita by extracts and powdered fruits of Gleditsia sinensis (Chinese honeylocust). Nematropica. 47(2):155-164.

Interpretive Summary: Plant-parasitic nematodes are microscopic worms that attack crop plants and result in an annual U.S. crop loss of ten billion dollars. One approach for solving the problem of the lack of safe and effective control methods for nematodes is to discover plants that are toxic to nematodes because of the naturally occurring compounds within the plants; these plants can often be used as amendments for application to soils. Previous research indicated that a crude extract from seed pods of the Chinese honeylocust inhibits the movement of nematodes. In this paper, a team of ARS and Chinese scientists examined these nematode-toxic effects in greater detail in laboratory and greenhouse experiments with the most economically important nematode species, the root-knot nematode. In the laboratory, a seed pod extract was discovered to inhibit nematode hatching and movement; in the greenhouse, seed pod powder suppressed nematode numbers, although the effects varied with host plant (pepper, cucumber and water spinach) and there was some evidence of toxicity to pepper plants. The results are significant because they provide the first indication that the Chinese honeylocust may be useful for reducing nematode populations when used as a soil amendment. Consequently, this study will be used by researchers developing safe, naturally occurring materials for use in reducing crop losses caused by nematodes.

Technical Abstract: Although the Chinese honeylocust (Gleditsia sinensis) is receiving extensive pharmacological investigation because of its use in traditional Chinese medicine, little work has been undertaken to investigate use of G. sinensis products as soil amendments or as sources of nematode-antagonistic phytochemicals. In this study, seed pods (fruit) were dried and ground, and an ethanolic extract was prepared and examined for its effects on egg hatch, movement and viability of Meloidogyne incognita in in vitro experiments. In addition, the dried fruit powder and the ethanolic extract were both tested in greenhouse experiments for effects on M. incognita populations and on growth of pepper (Capsicum annuum), and the dried fruit powder was also tested on water spinach (Ipomoea aquatica). In the in vitro experiments, concentrations of 1.0 and 10.0 mg/ml ethanolic extract of the fruit powder reduced J2 viability by 96.5% to 98.4%; the higher concentration also suppressed egg hatch by 60.3%. In greenhouse pot tests, M. incognita densities on pepper and water spinach were not suppressed by amending the soil with fruit powder or drenching with fruit powder extract (the latter tested only on pepper), as indicated by enumeration of galls/g root and eggs/g root. Additionally, G. sinensis fruit powder and extract exhibited phytotoxicity to pepper, resulting in decreased shoot length and fresh weight and root fresh weight. Shoot and root fresh weights of water spinach were also reduced by amendment of fruit powder into soil. Consequently, although G. sinensis produces nematotoxic compounds, neither fruit powder nor fruit powder extract applied to soil demonstrated potential as plant-derived sources for suppressing nematode populations in plant roots. Isolation and identification of the nematode-antagonistic compounds in the fruit of G. sinensis would indicate whether these chemicals are potential sources of biologically based nematicides.