Terpenoid aldehydes in cotton roots susceptible and resistant to the root-knot nematode, Meloidogyne incognita.

We investigated the role of terpenoid aldehydes in the resistance of cotton (Gossypium hirsutum) to the root-knot nematode (Meloidogyne incognita). Three-day-old, root-knot-resistant ('Auburn 623') and -susceptible ('Deltapine 16') seedlings were inoculated with M. incognita. Comparable portions of inoculated and noninoculated roots were harvested 2, 4, 7, and 10 days later. Terpenoid aldehydes were extracted, separated by thin-layer chromatography, eluted as their phloroglucinol derivatives, and measured colorimetrically. In noninoculated seedlings of each age, the susceptible cultivar contained more total and more of each of five specific terpenoid aldehydes (hemigossypol, methoxyhemigossypol, gossypol, lnethoxygossypol, dimethoxygossypol) than did the resistant cultivar. In both cultivars, the concentration of terpenoid aldehydes increased as seedlings aged. After inoculation, the concentration of terpenoid aldehydes was usually highest in the noninoculated, followed by the infected susceptible, infected resistant, and noninfected resistant seedlings in that order. The changes in concentration that occurred in response to infection, particularly at 7 and 10 days after inoculation, did correlate with host resistance, i.e., there was a net loss of total and each specific terpenoid aldelhyde in tlae susceptible cultivar, and a net gain in the resistant. Our data do not exclude the possibility that localized synthesis of terpenoid aldehydes is involved in resistance to root-knot nematodes.