Ching-Hua Mao, Yu-Chi Lu, Yong-Shi Li, Ya-Chun Chang
Pitaya (Hylocereus spp.), also called dragon fruit or pitahaya, is an important fruit crop in Taiwan. This climbing epiphytic cactus plant is native to the forests of Latin America, and is now commercially cultivated in many countries. Because pitaya is mainly propagated by cutting, virus-infected mother plants can spread viruses via cuttings very easily. In Taiwan, the first viral disease of pitaya which was caused by Cactus virus X (CVX), a member of the genus Potexvirus, was reported by the research team of Professor Ruey-Fen Liou at National Taiwan University (NTU) in 2001. They executed the cloning and sequencing work of CVX-Hu isolate, prepared the antiserum against CVX virions and developed a DAS-ELISA detection method. Several years later, in the NTU experimental farm, a new pitaya isolate of CVX from pitaya was identified, and the complete genomic sequences of CVX-NTU isolate was acquired. During 2006 to 2008, we isolated another two potexviruses, Zygocactus virus X (ZyVX) and Pitaya virus X (PiVX), from the pitayas grown in the northern area and did further viral characterization works. According to our results, this is the first ZyVX isolate identified in Taiwan and also the first report of ZyVX infecting pitaya in the world. As to PiVX, it was identified as a new species of the genus Potexvirus and named after its origin from pitaya. To study the individual infection frequency of CVX, ZyVX and PiVX in pitaya, we developed a multiplex RT-PCR method so as to detect and differentiate them simultaneously. A magnetic nanoparticle-capture RT-PCR (MNC RT-PCR) was later developed to save on detection time and cost. Pitaya samples collected from several production areas in Taiwan were investigated for the infection rate and distribution of potexviruses. The field survey results showed that almost all pitaya samples were infected by these potexviruses and mixed infections were quite common.