ANALYSIS OF RFLPS IN NUCLEAR AND MITOCHONDRIAL-DNA AND THE TAXONOMY OF PHYTOPHTHORA-FRAGARIAE

Severe root rot of red raspberry is caused by a fungus which has recently been classified as P. fragariae var. rubi because it is thought to be closely related to the fungus causing red core disease of strawberry, P. fragariae var. fragariae. DNA from P. fragariae var. rubi was cloned in E. coli, and clones showing little or no hybridization to other Phytophthora species in dot blots were selected for use as probes which might detect restriction fragment-length polymorphisms (RFLPs) within and between the so-called varieties. Variation revealed by restriction enzyme digestion of mtDNA was also employed. Both pathogens were very homogeneous, providing support for their recent and rapid worldwide expansion. Although readily distinguishable, they were more closely related to one another than to any other Phytophthora spp.; their separation at the variety level appears appropriate. Two of the probes also proved suitable for differentiating among other Phytophthora spp. associated with raspberry root rot.