USE OF RAPD ANALYSIS TO TRACE THE ORIGIN OF THE WEEVIL PATHOGEN ZOOPHTHORA-PHYTONOMI IN NORTH-AMERICA

In North America, the fungal pathogen Zoophthora phytonomi, has been k nown to cause significant levels of infection in introduced clover lea f weevil populations, Hypera punctata, since 1885. This pathogen was n ever noted in introduced populations of alfalfa weevil, H. postica, sy mpatric with clover leaf weevil, until 1973 when it was found in alfal fa weevil in Ontario. From 1973 through 1981, Z. phytonomi was progres sively found further south from Ontario. Whether these reports of Z. p hytonomi infecting H. postica actually demonstrate spread by a novel g enotype has previously been proposed and disputed. PCR-RAPD analysis w as used to compare isolates of Z. phytonomi from both hosts in North A merica, and from H. postica in Israel with Z. radicans and Conidiobolu s osmodes as outgroups. Both phenetic and cladistic analyses demonstra te that two main genotypes of Z. phytonomi occur in North America; one genotype including only H. punctata isolates wi:ha second more homoge neous and principally including isolates from H. postica. The genotype principally including isolates from H. postica was more closely relat ed to isolates from H. postica in Israel than to the other North Ameri can group, but also included one isolate from H. punctata. Based on af finity with Israeli genotypes, this latter strain may have originated in the Eurasian areas where H. postica is endemic. The degree of host specificity of these two North American genotypes of Z. phytonomi will require further investigation.