MITOCHONDRIAL AND NUCLEAR-DNA RESTRICTION ENZYME ANALYSIS OF THE CLOSELY-RELATED PHYTOPHTHORA SPECIES P-INFESTANS, P-MIRABILIS, AND P-PHASEOLI

To determine relatedness of the phytopathogenic fungi Phytophthora inf estans, P. mirabilis, and P. pbaseoli restriction fragment patterns of mitochondrial DNAs of several isolates and hybridization patterns of nuclear DNAs after Southern hybridization with a specific homologous p robe were analyzed. All but two isolates of P. infestans and P. mirabi lis show very similar restriction fragment patterns differing only in the length of one fragment due to small insertion/deletion(s). Two iso lates of P. mirabilis have one additional site for ScrFI. On the contr ary at least six sites differ in P. pbaseoli when compared to the othe r two species. The mitochondrial genome of P. phaseoli is considerably smaller (approx. 6 kbp) than those of P. infestans and P. mirabilis. A cloned 430 bp multicopy DNA sequence, derived from P. infestans, hyb ridized specifically with P. infestans, P. mirabilis, and P. pbaseoli out of 61 species of Peronosporales (Phytophthora, Halophytophthora, P ythium, Albugo, Bremia, Peronospora, Plasmopara) tested and therefore has potential as a diagnostic probe. Restriction patterns revealed by this probe are invariant intraspecifically but differ between the thre e species. We consider P. mirabilis a forma specialis of P. infestans because of the very high similarly in its mitochondrial DNA restrictio n patterns.