SUPPRESSION OF MELOIDOGYNE INCOGNITA BY EXTRACTS AND POWDERED FRUIT OF GLEDITSIA SINENSIS (CHINESE HONEYLOCUST)

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 second-stage juvenile (J2) viability by 96.5% to 98.4%; the higher concentration also suppressed egg hatch by 60.3%. In greenhouse pot tests, M. incognita population 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.