NUCLEIC-ACID HOMOLOGIES OF 18 CUCUMBER MOSAIC-VIRUS ISOLATES DETERMINED BY COMPETITION HYBRIDIZATION

Cucumber mosaic virus (CMV) strains S and WT were selected as reference viruses to provide the double-stranded and 3H-labelled single-stranded RNAs in competition hybridization experiments which determined the degree of nucleotide sequence homology among 19 CMV isolates of different origin. A group of 3 and a group of 14 isolates (S and WT groups, respectively) were found to have extensive, if not total, sequence homology among their members and little if any homology between the groups. Only one isolate obtained from Ixora (CMV-Ix) was partially homologous (43%) with the WT group and had no homology with the S group. The finding of two main groups of CMV isolates, based on nucleic acid homolgy, parallels the divisions on the basis of symptomatology and serological properties proposed previously by other workers.