ROLE OF A PHYTOALEXIN IN CONTROLLING LESION DEVELOPMENT IN LEAVES OF VICIA FABA AFTER INFECTION BY BOTRYTIS SPP

Phytoalexin extracted from infection droplets and diseased tissues behaved as an ether‐soluble acid, and was easily separated by solvent partition from other ether‐soluble substances. The phytoalexin was formed in leaves by apparently healthy cells in advance of hyphae of either Botrytis fabae or B. cinerea, and in response to physical injury. Concentrations of phytoalexin around deep lesions caused by B. fabae were completely fungistatic. B. fabae caused apparent degradation of phytoalexin in lesions, and removed phytoalexin from solutions in vitro much more readily than did B. cinerea. The lower sensitivity to the phytoalexin, and the possibly related greater ability to metabolize the phytoalexin, are major factors in the greater pathogenicity of B. fabae than of B. cinerea. The same properties largely explain the ability of B. fabae to cause the so‐called ‘aggressive’ phase of the chocolate‐spot disease under some conditions. Copyright © 1969, Wiley Blackwell. All rights reserved