Acidovorax avenae subsp. cattleyae causes bacterial brown spot disease on terrestrial orchid Habenaria lindleyana in Thailand

Abstract

© 2018, Società Italiana di Patologia Vegetale (S.I.Pa.V.). Bacterial diseases of orchid are widespread and constitute a serious limiting factor to the production of the terrestrial orchid, Habaneria lindleyana. Bacteria were isolated from terrestrial orchids exhibiting disease symptoms in the Chiang Mai province of Thailand. Initial symptoms were circular, water-soaked leaf spots, which became brown and surrounded by yellow haloes, then enlarged to irregularly-shaped brown blotches followed by necrosis. Pathogenicity tests proved that a bacterium caused the same symptoms on H. lindleyana leaves after inoculation. The bacterium was identified as Acidovorax avenae subsp. cattleyae based on bacteriological analyses and 16S rRNA sequence comparison. Additional pathogenicity tests indicated that an isolate of A. avenae subsp. cattleyae from H. lindleyana could cause brown spots in other orchid genera. To our knowledge, this is the first study conducted to evaluate the importance of A. avenae subsp. cattleyae as an orchid pathogen in the Chiang Mai province of Thailand.