The protein based phylogenetic trees based on 21 isolates of Cucumber mosaic virus estimated for 1a, 2a, 3a and 3b proteins, suggest that the 3a movement protein (MP) and 3b coat protein (CP) were congruent and indicated no significant difference (p-value= 0.699 > 0.05) in the branch lengths. The conservation might be due to the coordination of CP with MP. Hence it supports the earlier sub grouping of CMV based on 1a and 3a proteins in addition to coat protein. In the CP and MP phylogenies, on the basis of branch length the subgroup IA appears ancestral to the subgroup IB. Drastic variations of branch length was also observed in a few isolates. There are significant variations in the branch length between 1a and 2a proteins indicating that the RNAs had independent evolutionary histories.
Balaji, S., Bhat, A., & Eapen, S. (2008). A phylogenetic reexamination of Cucumber mosaic virus isolates based on 1a, 2a, 3a and 3b proteins. Indian J. Virol, 19(1), 17–25.