An integrated study of morphological and isozyme patterns found within a worldwide collection of Phytophthora citrophthora and a redescription of the species

Abstract

A worldwide collection of 77 isolates of Phytophthora citrophthora from 30 different host species was investigated for variation in morphology and isozyme patterns. All isolates produced non-caducous, papillate sporangia. Only those isolated from cacao ( Theobroma cacao ) in Brazil produced chlamydospores, whereas cacao isolates from Indonesia did not produce chlamydospores. Over 70% of the isolates were sterile; the remainder could be designated as the A2 mating type based on pairings with P. capsici , though P. citrophthora itself did not produce oospores. The species was separated into three distinct isozyme subgroups: CTR1 containing isolates from widely distributed geographical locations on a broad range of hosts, CTR2 composed exclusively of Brazilian isolates from cacao, and a new subgroup CTR3 consisting of Indonesian isolates also isolated from cacao. A total of 14 enzymes and 17 putative loci were used to compare the isolates and seven loci were polymorphic. Peptidase was diagnostic for CTR1, malate dehydrogenase (MDH1) for CTR2 while the migration patterns for both glucose-6-phosphate dehydrogenase and hexokinase (HEX2) differentiated CTR3. A redescription of R. citrophthora is presented based on all 77 isolates including physiological, morphological and isozyme characters that can assist identification.