Microchrysosphaera graminicola, an enigmatic new genus and species in the Hypocreales from Panama

Abstract

An unusual fungus with a novel set of morphological, ecological, and DNA sequence characteristics was found to be causing necrosis of distal portions of living leaves and sterility of Parodiophyllochloa cordovensis (Poaceae) in Panama. The small, superficial, soft-textured yellow perithecia develop directly on the surface of the necrotic plant tissue. The unitunicate asci are filled with hyaline, long-fusiform, typically 6–12-septate ascospores that disarticulate into secondary part-ascospores that later produce tertiary spores. This undescribed fungus could not be cultured, nor was an asexual state observed. Morphological characteristics are inconsistent with any existing generic concept, but suggest a close phylogenetic relationship with species of Hypocreales. This was confirmed by molecular phylogenetic analysis of nrLSU rDNA sequences. While host relationship and disarticulation of ascospores suggest an affinity between this fungus and species of Clavicipitaceae, its colonization of necrotic tissue of a living host, lack of stromata, non-thickened apices of the asci, and long-fusiform (not filiform) ascospores suggest otherwise. Furthermore, this fungus differs morphologically from species in Bionectriaceae and Nectriaceae in its disarticulating long-fusiform ascospores, part-ascospores producing tertiary spores, and occurrence on living grasses. Our phylogenetic analysis of combined ITS, nrLSU, and TEF1 sequences yielded evidence for placement of the new species within the Hypocreales, close to Bionectriaceae and Nectriaceae. However, our analysis did not specifically clarify and support the species’ membership within either family. This fungus is described as Microchrysosphaera graminicola, a new genus and species belonging to the Hypocreales, incertae sedis.