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Research Project: CHARACTERIZING, DETECTING, AND ELIMINATING PATHOGENS TO ENABLE THE SAFE INTRODUCTION OF PLANT GENETIC RESOURCES

Location: National Germplasm Resources Laboratory

Title: Molecular characterization and phylogenetic analysis of Citrus viroid VI variants from citrus in China

Author
item CAO, MENGJI - Southwest University
item WU, QIONG - Southwest University
item YANG, FANGYUN - Southwest University
item WANG, XUEFENG - Southwest University
item Li, Ruhui
item ZHOU, CHNAGYONG - Southwest University

Submitted to: European Journal of Plant Pathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/19/2017
Publication Date: 5/12/2017
Citation: Cao, M., Wu, Q., Yang, F., Wang, X., Li, R., Zhou, C. 2017. Molecular characterization and phylogenetic analysis of Citrus viroid VI variants from citrus in China. European Journal of Plant Pathology. doi: 10.1007/s10658-017-1236-3.

Interpretive Summary: Viroids are the smallest known group of plant pathogens, comprised of only a few hundred nucleotides of RNA that do not encode for any proteins. Several viroids infect citrus and cause diseases. Citrus viroid VI (CVd-VI) is a recently identified viroid reported from citrus and persimmon. CVd-VI infection causes mild leaf bending and petiole necrosis in citrus, but may cause more severe symptoms when occurring as a mixed infection with other viroids. This research is the first report of CVd-VI in China, where a total of nine infected trees were identified from four provinces. In this study, 90 viroid sequences were obtained and used to analyze the variation among these CVd-VI isolates and those reported from Japan. The isolates separated into two groups according to host species-one citrus group and another persimmon group. This research increases our knowledge of citrus viroids and can help devise better strategies to minimize the spread of infections, thereby maintaining production of viroid-free orchards.

Technical Abstract: Citrus viroid VI (CVd-VI) was originally found from citrus and persimmon in Japan. We report here the identification and molecular characterization of CVd-VI from four production regions of China. A total of 90 cDNA clones from nine infected citrus cultivars were sequenced. The sequence homologies of the Chinese CVd-VI and the reference sequence (NC_004359) vary from 94.2% to 97%. The divergences among the Chinese isolates were up to 95.2%. Phylogenetic analysis of the 23 CVd-VI variants from China and Japan showed that they were grouped into two clades, one with 20 citrus variants and another with three persimmon variants, regardless of the geographic origins. Therefore, like HSVd, CVd-VI can also be divided into two types- citrus and persimmon. Sequence alignment showed that most nucleotide changes between the two clades occurred in the P, V and TL domains, and analysis indicated that these mutations influenced the predicted secondary structures under minimum energy.