Systematic analysis of the falcate-spored graminicolous Colletotrichum and a description of six new species from warm-season grasses

Abstract

Species limits in the fungal genus Colletotrichum are traditionally distinguished by appressorial and/or conidial morphology or through host plant association, but both criteria are criticized for their inability to resolve distinct taxa. In previous research eight novel falcate-spored Colletotrichum species were identified from graminicolous hosts using multilocus molecular phylogenetic analysis. In the present work formal descriptions and illustrations are provided for six of the new taxa: C. hanaui sp. nov., C. nicholsonii sp. nov., C. paspali sp. nov., C. jacksonii sp. nov., C. miscanthi sp. nov. and C. axonopodi sp. nov.; and an emended description with epitypification is provided for C. eleusines. Comparison of hyphopodial appressoria and host association against phylogenetic species boundaries and evolutionary relationships in the graminicolous Colletotrichum group demonstrate that, while these characters can be useful in combination for the purpose of species diagnosis, erroneous identification is possible and species boundaries might be underestimated if these characters are used independently, as exemplified by the polyphyletic taxa C. falcatum. Appressoria have been subject to convergent evolution and were not predictive of phylogenetic relationships. Despite these limitations, the results of this work establish that in combination appressorial and host range characters could be used to generate informative dichotomous identification keys for Colletotrichum species groups when an underlying framework of evolutionary relationships, taxonomic criteria and nomenclature have been satisfactorily derived from molecular systematic treatments.

• appressoria
• Colletotrichum
• phylogenetic analysis
• warm-season grasses

Thanks to Patricia Eckel of the Missouri Botanical Garden for the Latin translations, the New York Botanical Garden Steere Herbarium and the USDA National Fungus Collection (BPI) for the loan of herbarium specimens; Lisa Vaillancourt, MAFF GeneBank, the Colletotrichum Germ-plasm Database at the University of Arkansas and Dave TeBeest for providing several cultures used for this research. This work was financially supported by the Rutgers Center for Turfgrass Science and the New Jersey Agricultural Experiment Station. Support for JAC’s graduate research was provided in part by a United States Environmental Protection Agency (EPA) Science to Achieve Results (STAR) Graduate Fellowship, the Ralph Geiger Endowment and a Land Institute Natural Systems Agriculture Graduate Fellowship. The research described in this paper has been financially supported in part by the EPA STAR Graduate Fellowship Program. EPA has not officially endorsed thisPUBLICation and the views expressed herein may not reflect the views of the EPA.