Phenolic conwent in the roots and leaves of tolerant and susceptible citrus cultivars attacked by Radopholus similis

Abstract

The free and bound phenolics were quantitatively determined in the roots and leaves of both healthy and Radopholus similis-infected citrus cultivars, three of which were susceptible and three tolerant to the pathogen. Forty-one phenolics were detected, thirty-two of which were present in significant amounts. The same kinds of phenolics, with few exceptions, were isolated from the six cultivars whether healthy or infected and changes in the individual phenolics in the susceptible and tolerant groups were principally quantitative. In R. similis-infected plants, eleven of the bound phenolics in the roots of tolerant cultivars were appreciably increased while in the susceptible cultivars, the individual bound phenolics either remained unchanged or were lowered. The net effect of infection was a 27–300 per cent increase in the bound phenolics in the roots from tolerant cultivars while in the roots from the susceptible group, the bound phenolics were reduced 16–34 per cent. There was no consistent pattern of accumulation or reduction of the total free or individual free phenolics in infected roots from any of the cultivars. The total bound phenolics in the leaves from both the tolerant and susceptible cultivars were not significantly increased as a consequence of infection, although increases in specific individual bound phenolics were observed. After infection, the free phenolics in the leaves from the tolerant cultivars were increased from 2 to 7 per cent of the total phenolicp, while in the susceptible cultivars, the free phenolics remained at the same level.