THE ROLE OF PHLORIDZIN IN THE HOST-PARASITE PHYSIOLOGY OF THE APPLE SCAB DISEASE

Abstract

A stimulating substance in apple leaves which enhances the growth of Venturia inaequalis (Cke.) Wint. was identified as phloridzin. The metabolism of this compound to phloretin, phloroglucinol, p-hydroxyphenyl propionic acid, p-hydrox-y benzoic acid, and protocatechuic acid is hypothesized on the presence of phloretin and phloroglucinol in the culture filtrates of V. inaequalis when it is grown in the presence of phloridzin. The only breakdown product which stimulated the parasite was p-hydroxyphenylpropionic acid and it is concluded that its utilization by V. inaequalis may be the basis for the stimulatory action of phloridzin.The effect of these compounds and m-inositol on the growth and sporulation of V. inaequalis was studied. All of the compounds induced resistant reactions in the 384-1 selection but not in the Geneva variety. This may represent a specificity of the host to the action of these chemicals, indicating that they are correlated with the specificity of the host to races of V. inaequalis. Preliminary studies on the effects of these compounds on the metabolism of the host indicated that new phenolic compounds are produced.