Morphological variation and experimental host range of Alternaria cinerariae

Abstract

Alternaria cinerariae, an important and well-known plant pathogen of cineraria, has been delimited by its narrowly to broadly ellipsoid or ovoid conidia with blunt-tapered false beaks, but without descriptions of its morphological variability and host range. Leaf spot diseases have recently been found on asteraceous plants Pericallis cruenta, Farfugium japonicum, and Gynura bicolor in Japan, with A. cinerariae-like isolates subsequently obtained from the lesions. In this study, we identified these isolates as A. cinerariae using an integrated species criterion based on morphology, phylogeny, and pathogenicity, and examined their morphological variability. Although isolates exhibited morphological differences with respect to sporulation pattern, conidial swelling, and chlamydospore formation, phylogenetic analysis using gpd, rpb2, and tef1 sequences clustered them together in a single clade with a previously recognized A. cinerariae strain. Inoculation tests on 17 species, including five Senecioneae species, were performed to determine the experimental host range of A. cinerariae. The results suggest that A. cinerariae has considerable morphological variation and preferential pathogenicity to Senecioneae plants, and also indicate that G. bicolor should be added as a natural host of A. cinerariae.