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Etiology

Botrytis Blossom Blight of Dendrobium. J. S. Ito, Graduate Student, Department of Plant Pathology, University of Hawaii, Honolulu, HI 96822; M. Aragaki, Plant Pathologist, Department of Plant Pathology, University of Hawaii, Honolulu, HI 96822. Phytopathology 67:820-824. Accepted for publication 11 February 1977. Copyright © 1977 The American Phytopathological Society, 3340 Pilot Knob Road, St. Paul, MN 55121. All rights reserved.. DOI: 10.1094/Phyto-67-820.

A previously unreported Botrytis blossom blight on Dendrobium spp. is prevalent in Manoa Valley, Oahu, Hawaii. The disease was characterized by elliptical, water-soaked, translucent, brown lesions on petals and sepals which eventually spread to cover large areas of the blossoms. Botrytis spp. isolates recovered from lesions were segregated into three groups on the basis of spore morphology. Group I isolates with ellipsoidal spores (10.0 × 7.7 μm) were identified as B. cinerea. Group II isolates were mostly ellipsoidal, large spored (17.3 × 12.7 μm), but also produced from 1-6% two-celled (19.9 × 12.0 μm) spores. Group III isolates also were mostly ellipsoidal and large spored (19.6 × 10.8 μm), but 3-14% were turbinate (15.4 × 14.6 μm). Spore germination and growth of all three types were optimal at 20-24 C. All isolates caused similar symptoms on Dendrobium by infecting buds and young (as well as mature) flowers. Of the three groups, Botrytis cinerea was the least virulent. A flecking response following artificial inoculation was attributed to aborted infection by Botrytis spp.