Research On Molecular Detection And Biological Characteristics Of Citrus Yellow Vein Clearing Virus

Citrus yellow clearing vein virus on citrus was been reported recently, and its molecular and biological characteristics are less studied. Lemons and Sour oranges were often infected by cyvcv, which caused leaf yellowing or vein cleaning. CYVCV can infect Many citrus species, and it is conformed CYVCV can spread from lemon to leguminous plants by aphid. Whereas transmission from citrus to citrus plants remains to be ascertained. Therefore, it is possible that CYVCV causes serious concequences in China.Citrus samples from 7 provences were detected by RT-PCR. Met gene and cp gene were sequenced and analyzed molecular characteristics of CYVCV. We also grafted CYVCV positive bud to different species citrus to study biological characteristics of CYVV.1. Totally, 450 samples from Hunan, Hubei, Jiangxi, Sichuan,Yunnan, guizhou and Zhejiang provinces were detected by RT-PCR, 77 of them were identified CYVCV positive and samples were infected CYVCV from six provinces(only except Zhejiang province). Positive rate of Hunan samples is 34.2% and positive rate of Dangyang samples is 53.3%, however, samples from some areas were CYVCV negative. Samples showed Water stain on back of leaves, vein cork, vein clearing and vein yellowing perhaps because of this virus infection. Meanwhile, some CYVCV positive samples did not showed any sympotoms, which indicated that cyvcv might infect citrus plants latently.2. The genes encoding methytransferase and coat protein were sequenced for 45 CYVCV isolates and 37 isolates from citrus samples collected from Hunan, Hubei, Jiangxi, Yunnan, Sichuan, Guizhou six provinces. Multiple alignment CYVCV met encoding gene nucleotide and amino acid similarity similarity are up more than 98% between China isolates, and to Turkey isolate Y1 isolate nucleotide similarity of 97-98% amino acid similarity 98-99.3%, CYVCV China isolates with respect to isolate Turkey there are several common variation sites were found; phylogenetic analysis showed CYVCV isolates divided into two groups:Ⅰand groupⅡ, which isolates all gathered in ChinaⅠgroup, Turkey isolate Y1 and isolate Pakistan PK gathered in groupⅡ.3.When grafted by lemon bud which infected CYVCV, sweet orange treetops present symptoms that were vein clearing, yellow vein, chlorotic spots, while no symptoms on lemon, fructus aurantii and HB pomelo. qRT-PCR analysis of different parts of the cultivars above which infected CYVCV showed that the number of virus in upper leaves was much than that in middle and lower leaves in biennial sweet orange. And as time goes on, virus in the upper leaves replicated rapidly. According to the accumulation of CYVCV on different citrus cultivars, virus content of CYVCV was confirmed: sweet orange > lemon > HB grapefruit > fructus aurantii. In addition, CYVCV content as well as increasing speed in sweet orange was significantly higher than the other three species of citrus.