Occurrence and Molecular and Biological Characteristics of Apple Rubbery Wood Virus 2 in Some Apple-Producing Areas of Northern China

Apple (<i>Malus domestica</i>) is one of the most economically valuable horticultural crops worldwide, and its production is affected by numerous plant viruses. The occurrence and molecular and biological characteristics of apple rubbery wood virus 2 (ARWV-2) in four apple-producing areas of northern China were analyzed. The average detection rate of ARWV-2 was 39.3%, with an 86.9% rate concurrently infecting apple stem grooving virus, apple stem pitting virus, and apple chlorotic leaf spot virus and an 8.1% mixed infection with apple rubbery wood virus 1. New primers were designed to amplify the nearly complete sequences of the variants a and b of the medium (Ma and Mb) and small (Sa and Sb) fragments in 34 ARWV-2-infected samples. The results showed that the detection rates of Ma and Sa (100%) fragments were higher than those of Mb and Sb (11.8%). The coding regions of Ma and Sa segments had 67.1 to 67.8% and 72.4 to 73.9% nucleotide (nt) sequence identity with that of the corresponding Mb and Sb, respectively. Samples infected with only Ma and Sa (<i>n</i> = 30) shared 96.2 to 99.8% and 95.6 to 100% nt sequence identity with mixed infection samples containing Mb and Sb (<i>n</i> = 4), respectively. In the Ma and Sa phylogenetic trees, all isolates from this study were clustered into Groups I and II, while isolates from other countries were concentrated in Groups III and IV. In the Ma tree, the genetic distances of Group I with Groups II, III, and IV were 0.026, 0.027, and 0.042, respectively. Finally, the ARWV-2 isolate containing only Ma and Sa was inoculated in seven indicator plants with infection rates ranging from 28.6 to 94.4%. Moreover, the infection was systemic, and all inoculated plants were asymptomatic. This study revealed the occurrence of ARWV-2 in apples from northern China, identified the divergent viral segments Mb and Sb at a lower rate, and addressed the herbaceous host indicators. These findings provide important data about virus prevalence and identification and will be helpful to the formulation of efficient viral control strategies.