苹果茎沟病毒 (apple stem grooving virus, ASGV) 是一种重要的潜隐类果树病毒，对柑橘、梨和苹果等多种果树的生产构成了严重的威胁。2018年，在中国南方广泛种植的黄金蜜柚 (Citrus grandis cv. Huangjinmiyou) 上观察到了严重的黄化、斑驳和花叶症状，推测其可能由病毒引起。取5株表现相关症状果树的叶片样品构建混库并送高通量测序分析，从其中鉴定到了3个ASGV变异体，通过RT-PCR和RACE技术验证了其基因组序列。序列分析显示，这3个变异体的基因组核苷酸序列一致性为81.03%–82.34%，其基因组结构与过往报道的侵染其它果树的变异体类似。基于病毒全基因组核苷酸序列和外壳蛋白氨基酸序列的系统发育分析显示，3个黄金蜜柚ASGV变异体分别与来自不同寄主和地区的ASGV变异体聚在一枝。重组分析显示，3个ASGV变异体可能来自于ASGV不同株系间的重组。在全国11个主要柑橘种植省份采集了507份黄金蜜柚样品进行RT-PCR检测发现，在每个省份表现上述相关症状的样品中，ASGV的检出率均在92.7%以上，而在40份没有症状的样品中，均未检测到ASGV。将其中6个省份的感病样品嫁接到ASGV的指示植物——Rusk枳橙上，新生的系统叶表现出典型的碎叶症状，进一步验证了黄金蜜柚中ASGV的侵染。进一步探究了病毒和症状与温度的关系，发现嫁接的感病黄金蜜柚样品在30°C–35°C条件下症状消失，同时RT-PCR也检测不到ASGV的存在。而后，再将其置于20°C–24°C的条件下一段时间后，黄金蜜柚症状恢复，且ASGV可以由RT-PCR检测到。本文揭示了黄金蜜柚黄化斑驳花叶病与ASGV侵染的相关性，并提示了该病害大面积流行的风险，为进一步的病害防控提供了相应参考。

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.