Postharvest fruit rot of apple in the Loess Plateau region of China caused by <i>Neocyphella psychrotropha</i> sp. nov., representing a new family in Agaricales (Basidiomycota)

Since 2021, a previously undocumented and economically significant fruit rot disease has emerged on apple (Malus domestica) during cold storage in the Loess Plateau region of China. An unidentified basidiomycetous fungus was consistently isolated from symptomatic fruits across multiple packinghouses. The ITS sequences from these isolates exhibited less than 90% identity with validated fungal species in GenBank. Concatenated multi-locus phylogenetic analysis and whole-genome phylogenomics placed the fungus within a monophyletic clade proposed as a new family (Neocyphellaceae fam. nov.) within the Agaricales order. Pathogenicity assays confirmed the fungus's capacity to consistently induce lesions on pre-wounded apple fruits and leaves. Notably, neither asexual nor sexual sporulation structures were observed on potato dextrose agar (PDA) or any other tested media. The fungus displayed distinct psychrotolerant characteristics. This organism exhibited optimal growth and virulence at 15-20°C, while exhibiting approximately 70% growth inhibition and 50% virulence attenuation at 28°C compared to 20°C. In vitro fungicide sensitivity assays revealed high sensitivity to demethylation inhibitors (DMIs; average EC50 for hexaconazole = 0.029 μg/mL) and quinone outside inhibitors (QoIs; average EC50 for pyraclostrobin = 0.12 μg/mL). The novel taxon was formally described as Neocyphella psychrotropha, and we propose the disease name "apple Neocyphella rot".