Genomic Analysis, Sequence Diversity, and Occurrence of Apple necrotic mosaic virus, a Novel Ilarvirus Associated with Mosaic Disease of Apple Trees in China.

China accounts for over 50% of apple production worldwide. Very recently, a novel ilarvirus, Apple necrotic mosaic virus (ApNMV), was isolated from apple trees showing mosaic symptoms in Japan. This study compared different types of mosaic symptoms observed in apple trees in China under field conditions. Complete nucleotide sequences were obtained for six isolates of ApNMV. The genomic components varied in size from 3,378 to 3,380 nt (RNA1), 2,778 to 2,786 nt (RNA2), and 1,909 to 1,955 nt (RNA3), respectively. Although nucleotide sequence similarities with subgroup 3 ilarviruses were low (49.2 to 64.3%), results of phylogenetic analysis indicated that Chinese ApNMV isolates were clustered in subgroup 3 together with Prunus necrotic ring spot virus (PNRSV) and Apple mosaic virus (ApMV). Apple mosaic disease occurred widely in apple producing areas of China with a very high percentage (92.1%, 268 out of 291) of symptomatic trees being infected with ApNMV but not with ApMV. The data suggested that ApNMV might be the main pathogen causing apple mosaic disease in China. The genomes of the six studied Chinese ApNMV isolates demonstrated substantial sequence diversity. Here, we demonstrated a strong association of ApNMV with the mosaic disease of apple trees in China.