Identification of agents causing brown rot of Cymbidium iridioides in Sa Pa, Lao Cai Province, Vietnam

Cymbidium orchid (Cymbidium iridioides) is widely cultivated in Northern mountainous provinces of Vietnam, especially in Sa Pa, Lao Cai province. However, severe outbreaks of brown rot disease in C. iridioides occurred in July, 2013 due to abnormal weather conditions that resulted in significant loss for growers. In order to identify exactly the causal agent of the disease, the infested samples were collected. Twenty-five bacterial isolates were selected and no fungus was present in the samples. Pectolytic activity of those bacterial isolates was determined on potato tuber slices and the virulence was assessed on cymbidium cut leaves in vitro. As results, three bacterial isolates [M3(1), M3(2) and M4(3)] induced different rot symptoms on potato tuber slices and cymbidium cut leaves. Based on their bacteriological characteristics and 16S rRNA gene sequence analysis, these bacterial isolates M3(1), M4(3) and M3(2) were identified as Pectobacterium carotovorum subsp. carotovorum, P. carotovorum and Pseudomonas sp., respectively. The results suggested that bacterial brown rot disease of C. iridioides in Sa Pa, Lao Cai province, might involve three causal bacterial species.