Evidence for the existence of two subpopulations in Phytophthora capsici and a redescription of the species

Morphological, physiological and isozyme data were obtained for 113 isolates of P. capsici . Isozyme analysis of 18 loci from 15 enzymes revealed two distinct subgroups, CapA and CapB. Both subgroups contained isolates from widely distributed geographical locations and from a range of hosts. There was considerable morphological and physiological diversity amongst the isolates, but also significant differences between the two isozyme subgroups. The majority of isolates in CapA possessed rounded sporangia and exhibited irregular sporangial ontogeny. Most CapB isolates produced ellipsoid-lanceolate sporangia and ca 50% had an umbellate ontogeny. Chlamydospore-forming isolates occurred exclusively in the CapB subpopulation. A minority of CapA or CapB isolates exhibited sporangial traits more typical of the other isozyme subgroup. Consequently, use of morphological characters alone would not always allow correct assignment of an isolate to its isozyme subgroup. Phytophthora capsici is re-defined based on the wide variation in characters found in this worldwide population sample. A single available isolate of P. mexicana was placed in isozyme subgroup CapA, though it differed morphologically from the P. capsici isolates in producing non-caducous sporangia.