Morphological and phylogenetic analyses of Saprolegniales (Oomycota) reveal taxonomic and nomenclatural novelties

Abstract

Saprolegniaceae s.l. is a species-rich family of the monophyletic order Saprolegniales (Oomycota, Straminipila). Members of this family are primarily saprotrophs on cellulosic, chitinous, and proteinaceous materials in both aquatic and terrestrial ecosystems. This family also includes pathogens infecting various hosts, such as plants, crustaceans, and fishes at various life cycle stages. A diversity survey of Saprolegniaceae s.l. from freshwater and soil of the Brazilian Atlantic Rainforest resulted in 20 species isolated and identified through morphological and molecular analyses. These analyses revealed two new genera (Beakesia and Cokeria) and two new species, Achlya delicata and Brevilegnia milaneziana. Beakesia is proposed to accommodate Achlya catenulata, while Cokeria includes species with subcentric and centric oospores previously assigned to Achlya (A. racemosa, A. radiosa, and A. sparrowii). Our findings highlight the importance of additional sampling and studies in biodiversity-rich areas such as the Brazilian Atlantic Rainforest. They also provide a new perspective on the evolutionary relationships and nomenclatural delineation of traditional Oomycota genera, and revisit the family subdivisions of Saprolegniales, formally introducing Achlyaceae.