Phylogenetic network analysis of South and North American Corynespora cassiicola isolates from tomato, cucumber, and novel hosts

Corynespora cassiicola isolates display morphological, pathogenic, and ecological diversity, inducing target spot-like diseases in more than 500 hosts worldwide, including tomato and cucumber. Nevertheless, there is a scarce number of studies about the genetic variability of Corynespora isolates in the New World. Here, we characterized a collection of 58 Corynespora isolates from tomatoes and distinct hosts in Brazil and Florida (USA). All isolates were identified as C. cassiicola according to the sequencing information of the internal transcribed spacer (ITS) region of 18S–28S nuclear ribosomal DNA as well as the translation elongation factor 1-alpha (tef-1α) and β-tubulin (tub2) genes. However, intraspecific resolution was observed in phylogenetic analyses according to the geographical and host origin of the isolates. The β-tubulin (tub2) haplotype network was in agreement with phylogenetic analyses, revealing a polyphyletic structure with three well-defined phylogenetic lineages. The concatenated trees (encompassing all three genomic regions) showed superior intraspecific resolution than the individual phylogenetic trees. Thirteen selected C. cassiicola isolates (representing all three phylogenetic lineages) displayed variability in colony morphology (color, texture, growth rate, and shape) and in conidial morphometrics. Three selected C. cassiicola isolates confirmed their pathogenicity to the original hosts and to other plant species. Novel natural and experimental host-pathogen interactions were identified, including cabbage, Commelina benghalensis , eggplant, Eruca sativa , Hibiscus sabdariffa , and melon. The diversity of C. cassiicola isolates indicates that these phylogenetic lineages may represent a complex of closely related species with distinct patterns of host and cultivar-specificity.