Morphological distinctions between Phytophthora capsici and P. tropicalis sp. nov.

Abstract

Phytophthora isolates with deciduous long-pedicellate sporangia can be separated into two groups by isozyme analyses, but an apparent overlap in morphological characteristics was previously deemed as sufficient justification for inclusion of both groups in P. capsici with an expanded description of the species. However, the occurrence of two morphologic groups in a species is unsettling, prompting a reexamination of the taxon. Comparative morphological and cultural studies of 100 Phytophthora isolates with deciduous, long-pedicellate sporangia which have been referred to P. capsici, revealed that they were separable into two taxa: Phytophthora capsici with broad sporangia, sporangial length to diameter ratio less than 1.8, predominately round sporangial bases, absence of chlamydospores, good growth at 35 C, and pathogenicity to Capsicum; and Phytophthora tropicalis sp. nov., distinguished from P. capsici by narrow sporangia less than 26 μm in diameter, sporangial length to diameter ratio of more than 1.8, predominately tapered sporangial bases, production of chlamydospores by most isolates, poor or no growth at 35 C, and weak or no virulence to Capsicum.