CercosporellaandRamularia

Abstract

Cercosporella and Ramularia (hyphomycetous anamorphs with relationship to Mycosphaerellaceae, Ascomycota) are difficult to distinguish based on light microscopic characteristics of conidiophores and conidia. Although both genera have been known for more than 120 y, new morphological characteristics were found by “simple” light and scanning electron microscopy now allowing an unambiguous differentiation between both genera. Newly discovered morphological characteristics of interaction structures and ultrastructure of conidiogenous loci are congruent with LSU rDNA sequence analysis of C. virgaureae and Ramularia species. DNA sequences of the type species of both genera, C. virgaureae and R. pusilla, were generated. For the first time a complex cup-shaped appressorium is reported for a member of plant pathogenic cercosporoid hyphomycetes, based on light, scanning and transmission electron microscopy. The appressorium of C. virgaureae is formed by strongly branched hyphae radiating from a supporting intercellular hypha and remaining closely attached to each other. With its concave side the appressorium adheres to a cell of the leaf mesophyll. This structure is significant in comparison with morphologically unspecific intercellular hyphae known in other cercosporoid hyphomycetes. Scanning electron microscopy of conidiogenous loci also provide additional characteristics for distinguishing Cercosporella and Ramularia. Conidiogenous loci are smooth in Cercosporella but similar to the Cladosporium-type (consisting of a circular rim and a central dome) in Ramularia.