Mawassi, M., The S. Tolkowsky Laboratory, A.R.O. The Volcani Center, Bet Dagan, 50250, Israel
Gafny, R., The S. Tolkowsky Laboratory, A.R.O. The Volcani Center, Bet Dagan, 50250, Israel
Bar-Joseph, M., The S. Tolkowsky Laboratory, A.R.O. The Volcani Center, Bet Dagan, 50250, Israel

The sequences of the coat protein genes of four seedling yellows (SY) and four non-SY (NSY) of citrus tristeza virus (CTV) isolates, which were collected in Israel over a period of 30 years, were analyzed. Pairwise comparisons showed extensive similarities in the nucleotide and amino acid sequences of six isolates designated the VT group. This group consists of three NSY isolates that cause a very mild CTV reaction on the sensitive combination of sweet orange (SwO) grafted on sour orange (SO), and three SY isolates that cause severe SY and SwO/SO reactions. MT, a CTV isolate that is consistently nontransmitted by Aphis gossypii, was found to be different in two amino acids (Val 103 and Glu 113) from each of the A. gossypii transmissible CTV isolates. Sequencing of the cDNA clones obtained from ST, a variably transmitted CTV isolate, showed extensive sequence variation among the tested clones. The sequence information indicates that the current CTV epidemics in Israel are caused by at least two CTV subspecies (VT and HT) displaying extensive differences in their coat protein genes. © 1993 Kluwer Academic Publishers.