Nematostatic activity of root extracts of banana (Musa spp.) genotypes as pre-infectional resistance mechanism against the burrowing nematode, Radopholus similis

Abstract

ABSTRACTBurrowing nematode (Radapholus similis) is a major threat to banana (Musa spp.) production throughout the world. All commercial banana cultivars are lacking of R. similis resistance. The conferred resistance available in non-commercial banana genotypes opens ways to develop new hybrids with R. similis resistance by conventional or molecular-breeding techniques. Understanding the mechanism of resistance is the primary step that can provide Musa breeders and molecular biologists with the necessary principles to create nematode-resistant plants. Phenols and lignin have been ascribed as post-infectional resistant mechanism in banana. However, information on anti-nematode compounds that are presented in resistant banana plants before challenge by R. similis is limited. Therefore, the roots of some resistant/tolerant genotypes were tested for anti-nematode bioactivity by root amendment study. The root homogenates of resistant/tolerant genotypes (Yankambi km-5 (YKM-5), Pisang Lilin, Pisang Jaribuaya, Rose, Matti, Hatidat, Veneettu Kunnan, Then kunnan, Manoranjitham, Anaikomban, Agneeswar, Pisang Mas, Gros Michel, Williams, Red Banana (Mutant), Green Red and Tongat) inhibited the infectivity of R. similis on susceptible Musa cv. Grand Nain (AAA). To confirm their bio-activity, R. similis was exposed directly to the root extracts (water, methanol, ethyl acetate and n-hexane) of the resistant/tolerant genotypes. Methanol, ethyl acetate and n-hexane root extracts of the resistant/tolerant genotypes affected the mobility of R. similis. Results confirmed that roots of resistant/tolerant plants have pre-infectional nematostatic compounds to resist R. similis. Further bio-assay-guided fractionation, isolation and identification of nematostatic compound from methanol, ethyl acetate and n-hexane root extracts of YKM-5 was attempted. The compounds N´- (3,6-dichloro-2,7-bis (2-(diethylamino) ethoxy) dodecahydro − 9H-fluoren-9-ylidene) pivalohydrazide isolated from methanol root extract; methyl 9,12-dimethylheptadecanoate isolated from ethyl acetate extract and; 1-isopropyl-2-propyldisulfane isolated from n-hexane extract were found to have nematostatic effect on R. similis. Further effort to validate that the production of these compounds contributes to resistance against R. similis in Musa germplasm would yield concrete markers for nematode resistance breeding programs.