An Apparent Relationship Between Methoxy-Substituted Terpenoid Aldehydes and the Resistance of Cotton To Meloidogyne Incognita

Abstract

Five cotton (Gossypium hirsutum) cultivars were rated for their resistance to the root-knot nematode (Meloidogyne incognita) on the basis of root-knot index, number of nematode egg masses/g of root, and number of nematode eggs/g of root. The most resistant cultivar was 'Auburn 623', followed by 'N6072' and 'Clevewilt'; 'Deltapine 16' was considered susceptible and 'M8' very susceptible. The terpenoid aldehydes (hemigossypol, methoxyhemigossypol, gossypol, methoxygossypol and dimethoxygossypol) were extracted from noninoculated and M. incognita-inoculated roots of the five cultivars. Individual terpenoid aldehydes were separated by thin layer chromatography and their concentrations determined colorimetrically. No significant correlations were apparent between host resistance and concentrations of the individual terpenoid aldehydes in either healthy or infected plants. The changes in the concentration of methoxy-substituted terpenoid aldehydes that occur as a result of infection were, however, significantly correlated with host resistance. These findings indicate that infection-induced synthesis of methoxy-substituted terpenoid aldehydes is involved in the resistance of cotton to the root-knot nematode.