Analysis of Sequence Variability in CP Gene of Citrus tristeza virus
ZHANG Jian-kun;HONG Ni;WANG Guo-ping
Hubei Province Laboratory for Detection and Control of Crop Diseases, College of Plant Sciences and Technology, Huazhong Agricultural University, Wuhan 430070, China
Abstract：Using total RNA as template extracted from three citrus (Citrus reticulata Blanco) samples (HN, JX-1 and JX-2) collected from Daoxian, Hunan and Chongyi, Jiangxi, CP gene of Citrus tristeza virus (CTV) was amplified by RT-PCR. The results of cloning and sequencing of amplified products demonstrated that three samples were affected with CTV. The results for single-strand conformation polymorphism (SSCP) analysis showed that genetic variation existed among the CP genes of CTV from three samples. The CP genes of CTV from HN and JX-1 contained a unique sequence type, but that from JX-2 had a population of sequence types, two of which were predominant. Sequence analysis results showed that clone HN-K had 98% nucleotide sequence identity with Portuguese isolate 28C and Israeli stem pitting isolate VT; clone JX-1-1 98%~99% with Indian isolates Pune and Bangalore; clone JX-2-7 and JX-2-17 97%~98% with Japanese seedling yellows isolate NUagA and Californian severe stem pitting isolate SY568. All four clones shared only 91%~93% identity with Floridian quick decline isolate T36, mild isolate T30 and Spain mild isolate T385. Phylogenetic tree analysis revealed that four Chinese clones appeared in three different clusters, shared high homology with seedling yellows or stem pitting isolates from different geographical origins but low homology with quick decline and mild isolates, and these suggested that there had no correlation between geographic origin of CTV and their nucleotide distances
