USE OF RESTRICTION-FRAGMENT-LENGTH-POLYMORPHISMS TO STUDY GENETIC-RELATIONSHIPS BETWEEN AUSTRALIAN AND JAPANESE ISOLATES OF PHYTOPHTHORA-VIGNAE

The genetic relationships among 10 Australian accessions of Phytophthora vignae (Pv) isolated from cowpea, two Japanese accessions of Pv isolated from adzuki bean and one accession of Phytophthora megasperma f. sp. glycinea (Pmg) isolated from soybean were assessed using Restriction Fragment Length Polymorphisms (RFLPs). Using five high-copy probes derived from genomic libraries of Pv and Pmg, RFLP banding patterns used to calculate the genetic distance, d, between isolates, showed that Pmg was very dissimilar to Pv (d = 0.102). In contrast, a close similarity among different isolates of Pv was observed (maximum d = 0.0039), with most polymorphisms being detected using probe pPmgS63. A dendrogram showed that the Japanese and Australian isolates of Pv each belonged to different clusters, with a similar range of intracluster genetic variation between members of the Australian cluster (d range 0.0001-0.0019) compared to the Japanese cluster (d = 0.0022). Because the genetic distance separating the Australian and Japanese clusters (average d = 0.0033) was less than twice that of the intracluster distances, it is proposed that these two geographically isolated groups of P. vignae have recently been derived from a single (unknown) source, rather than each being indigenous pathogens of their respective hosts cowpea and adzuki bean.