Restriction fragment length polymorphisms of the mitochondrial DNA of Phytophthora megasperma isolated from soybean, alfalfa, and fruit trees

Abstract

The mtDNAs from 24 small oogonial soybean-specific Phytophthora megasperma f.sp. glycinea (Pmg) isolates, 10 small oogonial alfalfa-specific P. megasperma f.sp. medicaginis (Pmm) isolates, 2 small oogonial nonhost-specific P. megasperma isolates from apple, 6 large oogonial nonhost-specific P. megasperma isolates from alfalfa or cherry, and 1 high-temperature P. megasperma isolate from alfalfa were investigated by restriction fragment length polymorphism analysis. Restriction patterns of the mtDNAs obtained by digestion with six restriction endonucleases showed limited variation within isolates of Pmg and Pmm. However, restriction patterns of Pmg and Pmm mtDNAs were very different. All nonhost-specific isolates of P. megasperma and the high-temperature isolate had restriction patterns that differed from each other and from those of Pmg and Pmm. The restriction patterns of the nuclear DNAs also distinguished these isolates from Pmg and Pmm. Phylogenetic analyses indicate that Pmg and Pmm are genetically distinct subgroups that represent biological species of P. megasperma and that several additional subgroups, possibly biological species, are present in the P. megasperma complex.