Genetic variation in Cylindrocladium floridanum and other morphologically similar Cylindrocladium species

Species of Cylindrocladium (C.) are anamorphs of the genus Calonectria (Ca.), and are important pathogens of numerous crops worldwide. C. floridanum is characterized by short, 1-septate, straight, cylindrical conidia and sphaeropedunculate vesicles. Isolates of Ca. kyotensis (anam. C. floridanum), Ca. candelabra (anam. C. scoparium), Ca. morganii (anam. C. candelabrum), C. ovatum and C. naviculatum were compared based on morphology, sexual compatibility, radial growth on media with different osmotic potentials, RAPD markers and A + T-rich DNA (AT-DNA) polymorphisms. In CLUSTER analyses of the data using the average linkage method, all five species clustered separately. RAPD profiles of ex-type cultures of the two acknowledged synonyms of Ca. kyotensis (Ca. floridana, Ca. uniseptata) shared 78-97% similarity, supporting their conspecificity. Strains of the opposite mating type of the respective heterothallic species studied shared high similarity coefficients of 77% for Ca. candelabra, and 92% for Ca. morganii. Two opposite mating types of C. ovatum with 99% similarity mated to produce a new teleomorph, described here as Calonectria ovata. Based on their RAPD and AT-DNA profiles, two major groups could be distinguished within Ca. kyotensis. Group two (including most of the Canadian isolates) shared only 12-45% similarity with the ex-type strains (group one) and clustered with mean correlation coefficients of r = 0.56 (RAPD analysis) and r = 0.37 (AT-DNA analysis), respectively. An isolate similar to Ca. kyotensis but with curved conidia had distinct RAPD and AT-DNA profiles, and shared less than 35% similarity (r = 0.00) with any of the species studied. These findings suggest that strains with curved conidia and sphaeropedunculate vesicles represent an undescribed taxon, and the name Cylindrocladium curvisporum is thus proposed for them.