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First Report of Cactus virus X on Hylocereus undatus (Cactaceae) in Taiwan

Hylocereus undatus Britt. & Rose (Cactaceae), commonly known as pitaya, produces edible fruits with red thorny peel and sweet white pulp containing numerous small soft seeds. In recent years, this fruit crop has become increasingly important in Taiwan. During a survey of diseases of pitaya, some plants were found with systemic mild mottling on the stems. A virus was mechanically transmitted that caused necrotic local lesions on Chenopodium amaranticolor and chlorotic lesions on C. quinoa. This virus also caused necrotic lesions with chlorotic halos on Gomphrena globosa and small chlorotic spots followed by systemic infection in Celosia argentea. Back inoculation from C. quinoa by sap transmission caused mild mottling on pitaya similar to that observed on the naturally infected plants and thus confirmed that the agent was the cause of the mottle symptom. Electron microscopic examination of negatively stained extracts from diseased plants revealed a flexuous rod-shaped virus with a length of 480 to 520 nm. Purified viral particles contained a single major protein of approximately 26 KDa as estimated by SDS polyacrylamide gel electrophoresis. In immunodiffusion tests, this virus reacted with antiserum to Cactus X virus (CVX) (ATCC #PVAS245), but did not react with antisera to Bamboo mosaic or Papaya mosaic viruses. These results establish the identity of the virus causing mottle disease on H. undatus as a strain of CVX.