Identification Of Fusarium Proliferatum Causing Leaf Spots On Cymbidium Orchids In Taiwan

Previous research indicated that black and yellow leaf spots on Cymbidium, Ondontioda, Dendrobium and Cattleya could be caused by Fusarium proliferatum worldwide. However, the agent causing leaf spot on Cymbidium spp. plants is still obscure in Taiwan. Thirty-five F.fujikuroi species complex (FFSC)-like isolates were collected from Cymbidium leaf spot from different greenhouses in Taiwan. All isolates were identified as F.proliferatum based on morphological characteristics and molecular analysis. Sequence of translation elongation factor 1-alpha gene showed 99%-100% homology with F.proliferatum. In addition, two assay techniques using either detached leaves or seedlings were used to evaluate the pathogenicity and host range of the isolates and consequently their effects on Cymbidium and other orchid plants. Pathogenicity assays revealed that all isolates induced black and necrotic spots on detached leaves of Cymbidium, showing 9.4%-29.5% severity on seedlings of Cymbidium. Results of host specificity tests on detached leaves of different plants indicated that the F.proliferatum isolates collected from Cymbidium plants caused severe black spots on Oncidium, Cymbidium, Dendrobium and Cattleya plants. The symptoms on Phalaenopsis plants were relatively mild. Results of host specificity tests on plant seedlings indicated that the F.proliferatum isolates of Cymbidium origin were also pathogenic to Oncidium, Cymbidium and Dendrobium, but not to Cattleya and Phalaenopsis. Phylogenetic analysis of the translation elongation factor (TEF) gene among all fungal isolates using maximum parsimony (MP) and Bayesian inference (BI) methods revealed that the isolates of F.proliferatum from Cymbidium spp. could be separated from other FFSC-like species with high phylogenetic support.