Although it is usually latent on citrus, apple, and pear, apple stem grooving virus (ASGV) poses a great risk to many sensitive cultivars.  Since severe leaf yellow mottle mosaic (LYMM) symptoms have been observed on Huangjinmiyou (HJY) pummelos (Citrus grandis cv. Huangjinmiyou), a commercial variety that is widely cultivated in South China, high throughput sequencing (HTS) was used to find potential pathogens and only three divergent ASGV variants were identified.  The three ASGV variants shared 81.03–82.34% genome-wide pairwise identities with each other, and were separately closest to other ASGV variants from different hosts and/or geographical regions, as indicated by viral phylogenies.  However, these new variants may have developed from viral interstrain interactions, based on the results of recombination analysis.  A large-scale survey using reverse transcription-PCR (RT-PCR) protocols designed for the three ASGV variants revealed a high incidence (92.7–100%) of ASGV in symptomatic HJY trees from 11 major citrus-producing regions in China.  None of ASGV were detected in asymptomatic trees.  Temperature treatments applied to the symptomatic HJY plants showed that ASGV is sensitive to high temperatures (30–35°C), at which not only the plants recovered, but also the viruses were not detected by RT-PCR, while at low temperatures (20–24°C), both the symptoms and viruses remained detectable.  These data show that ASGV is associated with the LYMM disease prevalent on HJY in China, and this is the significant basis especially of taking appropriate measures timely to manage the disease.  

Citrus leaf blotch virus (CLBV) is a member of the genus Citrivirus, in the family Betaflexiviridae.  It has been reported CLBV could infect kiwi, citrus and sweet cherry in China.  Of 289 citrus samples from six regions of China, 15 were detected to be infected with CLBV in this study.  The complete genome of four isolates of CLBV was obtained from Reikou in Sichuan (CLBV-LH), Yura Wase in Zhejiang (CLBV-YL), Bingtangcheng in Hunan (CLBV-BT), Fengjie 72-1 in Chongqing (CLBV-FJ), respectively.  While they all represented 8 747 nucleotides in monopartite size, excluding the poly(A) tail, each of the isolates coded three open reading frames (ORFs).  Identity of the four isolates ranged from 98.9 to 99.8% to each other and from 96.8 to 98.1% to the citrus references in GenBank by multiple alignment of genomes.  A phylogenetic tree based on the genome sequences of available CLBV isolates indicated that the four isolates were clustered together, suggesting that CLBV isolates from citrus in China did not have obvious variation.  This is the first report of the complete nucleotide sequences of CLBV isolates infecting citrus in China.

In order to understand molecular characterization of Citrus tatter leaf virus (CTLV) isolated from China, full-length cDNAs of CTLV-MTH and CTLV-XHC from Citrus reticulata and Citrus sinensis were cloned and sequenced based on whole-genome amplification by RT-PCR. The complete nucleotide sequences of CTLV-MTH and CTLV-XHC were determined to be 6 497 nucleotides in length and shared 79.9–91.0% and 78.8–98.0% nucleotide sequence identity, respectively, with other Apple stem grooving virus (ASGV) or CTLV strains available in GenBank. Unexpectedly, CTLV-MTH showed the highest nucleotide sequence identity (91%) with an apple isolate of ASGV, followed by 86.5% with ASGV-HH and 85.7% with ASGV-CHN. Furthermore, CTLV-MTH and three ASGV strains were grouped to a separate cluster in the phylogenetic tree, suggesting it has a closer relationship to ASGV than to CTLV. Therefore, it can be concluded roughly that CTLV may be not a distinct strains of ASGV. We proposed that Citrus tatter leaf virus should be renamed Apple stem grooving virus.

The complete nucleotide sequence of an isolate of Citrus vein enation virus (CVEV-XZG) from China has been determined for the first time. The genome consisted of 5 983 nucleotides, coding for five open reading frames (ORFs), had a similar genomic organization features with Pea enation mosaic virus (PEMV). Nucleotide and deduced amino acid sequence identity of the five ORFs compared to isolate CVEV VE-1 range from 97.1 to 99.0% and 97.4 to 100.0%, these values compared to isolate PEMV-1 range from 45.2 to 51.6% and 31.1 to 45.2%. Phylogenetic analysis based on the complete genome sequence showed that the isolate CVEV-XZG had close relationship with Pea enation mosaic virus. The results supports CVEV may be a new member of genus Enamovirus. The full sequence of CVEV-XZG presented here may serve as a basis for future study of CVEV in China.