The Possible Role of Phenolic Compounds in Resistance of Horticultural Crops to Dematophora necatrix Hartig

Crops e. g., pecan, persimmon and passionflower, which show resistance to the fungus Dematophora necatrix, the causal agent of white root rot disease, contain phenolic compounds which inhibit its growth. Roots of resistant crops contain higher concentrations of phenolic compounds than those of suceptible crops, e. g., apple, almond and peach. The fungus contains active polyphenoloxidase (PPO). The oxidation of phenols to quinones may decrease the inhibitory effect. Catechol, methylcatechol, hydroquinone and 8‐hydroxyquinoline significantly inhibited the growth of the fungus. In greenhouse experiments, seedlings were irrigated with, or dipped in, phenols. Catechol, methylcatechol and hydroquinone delayed the appearance of disease symptoms.