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 known to cause significant levels of infection in introduced clover leaf weevil populations, Hypera punctata , since 1885. This pathogen was never noted in introduced populations of alfalfa weevil, H. postica , sympatric with clover leaf weevil until 1973 when it was found in alfalfa weevil in Ontario. From 1973 through 1981, Z. phytonomi was progressively found further south from Ontario. Whether these reports of Z. phytonomi infecting H. postica actually demonstrate spread by a novel genotype has previously been proposed and disputed. PCR-RAPD analysis was used to compare isolates of Z. phytonomi from both hosts in North America, and from H. postica in Israel with Z. radicans and Conidiobolus osmodes as outgroups. Both phenetic and cladistic analyses demonstrate that two main genotypes of Z. phytonomi occur in North America; one genotype including only H. punctata isolates with a second more homogeneous and principally including isolates from H. postica . The genotype principally including isolates from H. postica was more closely related to isolates from H. postica in Israel than to the other North American group, but also included one isolate from H. punctata . Based on affinity 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.