Viroids are naked non-coding RNAs that can infect plants and cause severe disease. Apple scar skin viroid (ASSVd) is the causal agent of apple scar skin disease, which can infect apple trees and cause dappling and scar skin symptoms. In this study, we investigated the incidence of apple scar skin disease in apple-grafted small apple tree (Malus pumila ‘Saiwaihong’) in North China. Of 1322 tested trees, 90 exhibited obvious dapple symptoms in fruit skin (disease incidence of 6.8%). Dot-blot hybridization analysis proved that the peel from 25 diseased small apple tree were all positive for ASSVd, confirming that disease was associated with ASSVd infection. RT-PCR, cloning and sequencing were performed, and 12 complete sequences of ASSVd variants from Malus pumila ‘Saiwaihong’ were obtained. Sequence comparison showed that the 12 sequence variants shared 90.6–99.7% sequence similarity, phylogenetic analysis, performed based on the 12 ASSVd Malus pumila ‘Saiwaihong’ variants and other ASSVd variants reported from different hosts, did not show any clustering according to the respective host species. This is the first report of ASSVd infection in small apple tree (Malus pumila ‘Saiwaihong’).

中文翻译：

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华北小苹果树苹果疤痕类病毒的发生及分子特征

类病毒是裸露的非编码 RNA，可以感染植物并引起严重疾病。苹果疤痕皮肤病毒（ASSVd）是苹果疤痕皮肤病的病原体，可感染苹果树并引起斑驳和疤痕皮肤症状。在这项研究中，我们调查了华北地区苹果嫁接小苹果树（Malus pumila 'Saiwaihong'）的苹果疤痕皮病发病率。1322株试验树中，90株果皮出现明显斑纹（发病率为6.8%）。斑点杂交分析证明，25株患病小苹果树的果皮均呈ASSVd阳性，证实该病与ASSVd感染有关。进行RT-PCR、克隆和测序，获得了12条来自Malus pumila'Saiwaihong'的ASSVd变种的完整序列。序列比对表明，12个序列变异的序列相似性为90.6-99.7%，系统发育分析基于12个ASSVd Malus pumila'Saiwaihong'变异体和不同宿主报道的其他ASSVd变异体进行，未显示根据各自宿主的任何聚类物种。这是首次报道小苹果树（Malus pumila 'Saiwaihong'）感染ASSVd。