The significance of poly-phenolic metabolites of apple and pear in the host relations of Venturia inaequalis and Venturia pirina.

Abstract

SUMMARY: Series of apple and pear shoots were inoculated with the scab pathogens Venturia inaequalis and V. pirina and injected with polyphenolic metabolites extracted from apple and pear leaves, and with urea. The translocation and persistence of arbutin in Cox leaves was demonstrated chromatographically. Injection of metabolites of the highly susceptible varieties Cox and Williams back into the same varieties, markedly inhibited the pathogens, which suggests that these potential resistance factors do not occur only in varieties which are scab resistant. Inhibition of infection was most marked on leaves already developing a mature resistance and the injection treatments were most effective when applied near the time of inoculation. Injection of urea increased susceptibility to V. inaequalis, and further results indicated the importance of optimal balance mechanisms between polyphenolic and nitrogenous metabolites. Chlorogenic acid and isochlorogenic acid strongly inhibited both pathogens and there was some indication of synergism between them as resistance factors.