Multi-locus phylogenetic analyses of Colletotrichum gloeosporioides species complex causing crown rot on strawberry in Florida

Abstract

Colletotrichum gloeosporioides is the causal agent of Colletotrichum crown rot of strawberry in the southern United States. Recent multi-gene studies defined C. gloeosporioides as a complex species comprised of 37 species. In our study, we phylogenetically characterized C. gloeosporioides isolates from strawberry and other non-cultivated plants around strawberry fields. One hundred and fifteen strawberry isolates and 38 isolates from non-cultivated hosts were sequenced for five genomic regions: internal transcribed spacer (ITS), actin (ACT), calmodulin (CAL), chitin synthase (CHS-1), and glyceraldehyde-3-phosphate dehydrogenase (GAPDH). Phylogenetic analysis using the maximum likelihood and Bayesian inference methods, based on partition-specific models, revealed that most of the isolates in Florida (86%) were closely related to C. siamense, whereas 14 isolates were closely related to C. theobromicola (syn. C. fragariae), four isolates were C. fructicola, and three were C. clidemiae. However, only the first three species were pathogenic to strawberry. Morphological characteristics evaluated show that mycelial growth of all species is about 5 mm/day but colony morphology varies by species and incubation conditions. In vitro mating of the isolates demonstrated that C. fructicola is homothallic whereas C. siamense and C. theobromicola isolates are heterothallic. The biological importance of these different Colletotrichum species is currently being investigated to determine whether different management strategies are needed in strawberry production fields.