| Abstrakt: |
AbstractThe taxonomic status of Phytophthora mirabilis, one of six host-specific, foliar pathogens in Phytophthoragroup IV, has been uncertain. At various times this taxon has been given three different names: P. infestansvar. mirabilis; P. mirabilis; and P. infestansforma specialis mirabilis.Which of these names is correct depends on the degree of reproductive isolation between this taxon and the closely related species, P. infestans.The purpose of this paper was to evaluate the hypothesis that P. infestansand P. mirabilisare conspecific using a large battery of molecular markers. Analyses of one isozyme, 44 DNA fingerprint, and 85 presumed RAPD loci revealed little, if any, gene flow between P. infestansand P. mirabilis.Thus, host specificity apparently functions as an effective pre-and postulating reproductive isolating mechanism in nature. Gene flow analysis indicated that these two taxa are as reproductively isolated from each other as they are from the other four species in Phytophthoragroup IV. There were 26 fixed differences between P. infestansand P. mirabilisthat only could have developed in the absence of gene flow. Attempts to obtain F2progeny from F1interspecific hybrids failed, indicating the existence of genetic mechanisms of reproductive isolation in addition to host specificity. Despite the differences between P. infestansand P. mirabilis, growth rate on seven commonly used laboratory media could not be used to separate them in the laboratory. These data clearly reject the hypothesis that P. infestansand P. mirabilisare conspecific. Therefore, two of the three names given to this taxon, P. infestansvar. mirabilisand P. infestansforma specialis mirabilis, are invalid. We propose that the correct name for this species is P. mirabilis. |
