First report of apple luteovirus 1 and apple rubbery wood virus 1 on apple tree rootstocks in Korea.
Recently, several tentative new viruses have been discovered from apple trees (Malus pumila) using high-throughput sequencing; therefore, a study was conducted to investigate the existence of viruses infecting apple tree rootstocks, including new or emerging viral species, in Korea. Leaf samples, exhibiting yellowing and mottled symptoms, from 10 rootstocks (P1, Ottawa 11, Ottawa 13, Ottawa 5M, MM102, MM115, M5, M7, M10, and JM7) at the Apple Research Institute located in Gunwi and 20 rootstocks (M9) at a farmer's apple orchard located in Cheongju were collected in September 2017. The high-throughput RNA sequencing generated contigs derived from 2 recently discovered viruses, i.e. Apple luteovirus 1 (ALV-1) and Apple rubbery wood virus 1 (ARWV-1) not reported in Korea, as well as 5 viruses (Apple chlorotic leaf spot virus, Apple green crinkle associated virus, Apple stem grooving virus, Apple stem pitting virus and Apricot latent virus) already identified in apple trees cultivated in Korea. Of the 30 rootstock samples, 6 (M9) were found positive for ALV-1, and 11 (nine M9, one P1, and one JM7) were positive for ARWV-1. Among the virus-infected samples, 4 M9 samples were found to be coinfected by both ALV-1 and ARWV-1. This is thought to be the first report on the existence of ALV-1 and ARWV-1 infecting apple tree rootstocks in Korea.