Scleroramularia gen. nov. associated with sooty blotch and flyspeck of apple and pawpaw from the Northern Hemisphere

Abstract

Scleroramularia is proposed as a new hyphomycetous fungal genus associated with sooty blotch and flyspeck (SBFS) blemishes of apple and pawpaw fruit in the Northern Hemisphere. Morphologically the genus closely resembles Ramularia (Mycosphaerellaceae), based on its chains of hyaline conidia, with thickened, darkened, somewhat refractive conidiogenous loci. Scleroramularia is distinguished by forming black sclerotial bodies in culture, and having conidial chains that do not quickly disarticulate as observed in Ramularia. Based on the nuclear ribosomal DNA phylogeny (LSU), Scleroramularia represents an undescribed order in the Dothideomycetes, clustering between the Pleosporales and the Botryosphaeriales. Further analysis of morphology in combination with DNA phylogeny of the nuclear ribosomal ITS region and partial translation elongation factor 1-alpha (TEF) gene sequences delimited five species. These include S. asiminae on Asimina triloba (pawpaw fruit) in the U.S.A., and four other species occurring on apple fruit, namely S. abundans (on a local cultivar in Ardeşen, Rize, Turkey), S. shaanxiensis (on ‘Fuji’ in China), S. pomigena (on ‘Golden Delicious’ in the U.S.A.), and S. henaniensis (on ‘Fuji’ in China, and ‘Golden Delicious’ and ‘Gold Rush’ in the U.S.A.). Morphologically these taxa can be distinguished based on a combination of culture characteristics and conidial morphology in vitro, which is reflected in a key to the species treated.