Reevaluating Sirococcus: synonymizing Gnomoniopsis and elucidating the life cycle of S. daii

Historically, <i>Sirococcus</i> (established in 1855) and <i>Gnomoniopsis</i> (proposed in 1893) have been treated as distinct genera within <i>Gnomoniaceae</i>, primarily distinguished by the prevalence of their asexual and sexual morphs, respectively. However, recent molecular data have challenged this distinction. In this study, we re-evaluated the relationship between these two genera using a combined multi-locus phylogeny (ITS, <i>tef</i>1, and <i>tub</i>2) and morphological assessment. Phylogenetic analyses revealed that species of <i>Sirococcus</i> and <i>Gnomoniopsis</i> cluster within a single, robustly supported monophyletic lineage, sharing indistinguishable asexual characteristics. Consequently, we propose to synonymize <i>Gnomoniopsis</i> under <i>Sirococcus</i> following the principle of priority. Thirty-eight new combinations and a new species are proposed. Furthermore, we investigated the life cycle of <i>Sirococcus daii</i> <b>comb. nov</b>., a severe pathogen causing nut rot of Chinese chestnut (<i>Castanea mollissima</i>), for which the teleomorph was previously unknown. Through extensive sampling, we discovered the teleomorph on overwintered leaf litter, confirming the saprobic phase of its life cycle. Additionally, the fungus was isolated from healthy female flowers, young nuts, and husks, suggesting a latent or endophytic infection strategy. Based on these findings, we reconstructed the complete life cycle of <i>S. daii</i>. This study not only resolves the taxonomic controversy surrounding <i>Sirococcus</i> and <i>Gnomoniopsis</i> but also provides crucial epidemiological insights into <i>S. daii</i>, facilitating the development of effective management strategies for chestnut nut rot.