Occurrence of Gray Mold Caused by Botrytis cinerea on Okra in Korea

From 2014 to 2016, approximately 5% of okra fruit were observed displaying gray mold symptoms at the research field of Jeollabuk-do Agricultural Research and Extension Services, Korea. The symptoms observed were water-soaked, brown or gray spots, and abundant mycelial with conidia appearing on the infected fruit. Initial infection commenced from the base of fruit and gradually moved to the pod, where it finally resulted in collapse. Colonies on potato dextrose agar were gray to grayish brown, felted and cottony expanding 65-80 mm after one week. The fungus formed several black sclerotia ranging 1.0-3.5×0.5-3.0 mm on the Petri dish after two weeks. The conidia were one-celled, ellipsoidal or ovoid, colorless or pale brown, and 6.2-15.4×5.0-10.4 µm. Conidiophores arose solitary or in groups, straight or flexuous, septate, with an inflated basal cell brown to light brown, and measured 85-450×10.0-40.0 µm. On the basis of the morphological characteristics and phylogenetic analyses of internal transcribed spacer rDNA, the fungus was identified as Botrytis cinerea Pers. Pathogenicity of a representative isolate was proved by artificial inoculation, fulfilling Koch’s postulates. To our knowledge, this is the first report on the occurrence of B. cinerea on okra in Korea