NUCLEOTIDE-SEQUENCES FROM TOMATO LEAF CURL VIRUSES FROM DIFFERENT COUNTRIES - EVIDENCE FOR 3 GEOGRAPHICALLY SEPARATE BRANCHES IN EVOLUTION OF THE COAT PROTEIN OF WHITEFLY-TRANSMITTED GEMINIVIRUSES

The coat protein (CP) gene-containing circular DNA molecule of an isol ate of tomato leaf curl geminivirus (ITmLCV; 2749 nt) obtained from so uthern India, and the CP genes of tomato yellow leaf curl geminivirus isolates from Nigeria and two regions of Saudi Arabia were sequenced. ITmLCV DNA had the same arrangement of ORFs, and the same pattern of r epeats in the large intergenic region as is found in DNA-A of other wh itefly-transmitted geminiviruses (WTGs) from the Old World. However, t he sequence of ITmLCV DNA and the sequences of its predicted translati on products differed substantially from those of other WTGs, including one isolate obtained from a tomato plant in northern India. Compariso n of the four CP sequences deduced here with those of 18 WTGs previous ly studied indicated that their relationships can be represented by a tree with three branches that are unrelated to plant host species but which contain viruses from the Americas, Africa to the Middle East, an d Asia to Australia, respectively. It is suggested that WTG CP evoluti on has proceeded along different paths in these three main regions, an d that WTGs have adapted freely to new hosts in each region. Indeed, t he virus isolates causing similar diseases of tomato plants in the dif ferent continents are, with few exceptions, not closely related and wa rrant recognition as separate species.