Sequence variations among seventeen new radish isolates of Turnip mosaic virus showing differential pathogenicity and infectivity in Nicotiana benthamiana, Brassica rapa, and Raphanus sativus.

Infectious clones were generated from 17 new Korean radish isolates of Turnip mosaic virus (TuMV). Phylogenetic analysis indicated that all new isolates, and three previously characterized Korean radish isolates, belong to the basal-BR group. Pairwise analysis revealed genomic nucleotide (nt) and polyprotein amino acid (aa) identities of >87.9% and >95.7% respectively. Five clones (HJY1, HJY2, KIH2, BE, and prior isolate R007) had lower sequence identities than other isolates, and produced mild symptoms in Nicotiana benthamiana. These isolates formed three distinct sequence classes (HJY1/HJY2/R007; KIH2; and BE), and several differential aa residues (in P1, P3, 6K2 and VPg) were present only in mild isolates HJY1, HJY2, and R007. The remaining isolates all induced systemic necrosis in N. benthamiana. Four mild isolates formed a phylogenetic subclade separate from another subclade including all the necrosis-inducing isolates plus mild isolate KIH2. Symptom severity in radish and Chinese cabbage genotypes was not correlated with pathogenicity in N. benthamiana; indeed, Chinese cabbage cv. Norang was not infected by any isolate, whereas cv. Chusarang was uniformly susceptible. Four isolates were unable to infect radish cv. Iljin, but no specific aa residues were correlated with avirulence. These results may lead to identification of new resistance genes against TuMV.