Soft rot disease caused by Dickeya fangzhongdai in epiphytic orchids in Vietnam

Abstract

Soft rot diseases are becoming problematic in the cultivation of epiphytic orchids in Vietnam, but the causal agents are unknown. We investigated soft rot in Dendrobium anosmum, Phalaenopsis amabilis and Paphiopedilum concolor. Leaves of diseased plants with soft rot symptoms were sampled and cultures of Dickeya were obtained. The pathogen was identified as Dickeya fangzhongdai based on a phylogenetic analysis of 16s rRNA, dnaX, gapA and rplB. The pathogenicity of nine D. fangzhongdai isolates was confirmed in D. anosmum, Ph. amabilis and Pa. concolor in a nursery trial. The efficacy of a range of chemical agents was evaluated on the growth of D. fangzhongdai in vitro, and on D. fangzhongdai soft rot disease management in 1-year-old D. anosmum, Ph. amabilis and Pa. concolor plants. Cuprous oxide and Cu-bismerthiazol strongly inhibited the in vitro growth of D. fangzhongdai, and they reduced the soft rot lesion area of infected plants in vivo. These findings provide an interim option for producers to improve management of D. fangzhongdai soft rot disease in production nurseries in Vietnam.