Molecular and phenotypic characterization of three phylogenetic species discovered within the Neofusicoccum parvum/N. ribis complex

Abstract

Neofusicoccum parvum and N. ribis are closely related species whose identities often have been confused. These fungal plant pathogens were identified recently as the most abundant species of Botryosphaeriaceae (Ascomycetes) isolated from native Syzygium cordatum trees in South Africa. In another study using multiple gene genealogies from five nuclear loci three undescribed cryptic phylogenetic species as well as N. parvum were identified among 30 of these isolates. The aim of this study was to clarify the identity of the remaining isolates in the N. parvum/N. ribis complex from S. cordatum in South Africa, to describe newly identified cryptic species and to test their pathogenicity. Based on the RNA polymerase II subunit (RPB2) sequence comparisons, the isolates were identified as N. parvum or one of three previously recognized phylogenetic species that are described here as N. cordaticola, N. kwambonambiense and N. umdonicola. These species cannot be separated a priori based on morphological characteristics, although a posteriori analysis of variance showed that the differences in conidial length and width between the species were statistically significant. The isolates of the newly described species as well as N. parvum and N. ribis were tested for pathogenicity on S. cordatum under greenhouse conditions. Isolates representing the three new species were significantly more aggressive than N. parvum and N. ribis with N. kwambonambiense being the most aggressive. This study resolved long-standing questions of identity of species within N. parvum/N. ribis complex and lays a foundation for further studies on this group of pathogens.