VIEW ARTICLE

The Role of Phenols in Botrytis Brown Stain of Onion. C. A. Clark, Graduate Assistant, Department of Plant Pathology, New York State College of Agriculture and Life Sciences, Cornell University, Ithaca 14850; J. W. Lorbeer, Professor, Department of Plant Pathology, New York State College of Agriculture and Life Sciences, Cornell University, Ithaca 14850. Phytopathology 65:338-341. Accepted for publication 11 October 1974. DOI: 10.1094/Phyto-65-338.

Crushed, pigmented yellow onion scales inhibited germination of conidia of Botrytis cinerea. The amount of inhibition was correlated with the degree of resistance to brown stain of the onion cultivar employed. Conidial germination of Colletotrichum circinans was totally inhibited by crushed scales of all three colored cultivars, but not inhibited by the white cultivar. Although catechol inhibited growth of both B. cinerea and C. circinans, the latter was inhibited at a much lower concentration. Colony development of B. cinerea was inhibited at a lower concentration than mycelial growth. Mycelial growth of B. cinerea was not inhibited by protocatechuic acid or quercetin. When B. cinerea was grown for several days on agar containing catechol, a brown color developed in the medium identical to that on diseased onion scales. The color did not develop in media containing quercetin or protocatechuic acid nor when C. circinans was grown on catechol agar. Catechol probably functions as the substrate for the staining reaction. Furthermore, the fact that white onion scales do not inhibit B. cinerea yet do not become stained may be attributed to a lack of the substrate, catechol.