Etiology of Postharvest Fungal Decay in Kumquat: A Polyphasic Approach Integrating Aggressiveness, iPBS and SCOT Fingerprinting, and Multilocus Phylogeny

Abstract

As the global popularity of kumquat (Fortunella spp.; syn. Citrus japonica) continues to rise, knowledge of the pathogens responsible for postharvest losses remains limited. This study presents the first etiological investigation of postharvest fungal decay in kumquat, using a multi-regional survey and polyphasic characterization. A pathogenic complex responsible for postharvest decay was identified on this host for the first time, consisting of Alternaria alternata (n = 23), Geotrichum citri-aurantii (n =17), Penicillium digitatum (n = 30), P. italicum (n = 8), and P. expansum (n = 4). Identification combined morphological characterization with high-resolution molecular fingerprinting using start codon targeted (SCoT 32) and inter-primer binding site (iPBS 2395) markers, yielding polymorphic profiles that provided clear species-level discrimination consistent with multilocus phylogenetic analysis. In vitro assays identified distinct thermal optima for each pathogen. Geotrichum citri-aurantii growth was maximal at 30 degrees C, whereas P. expansum grew optimally at 20 degrees C. The remaining species-P. digitatum, P. italicum, and A. alternata-all achieved maximum growth at 25 degrees C, although P. italicum demonstrated a broad optimal range spanning from 20 to 25 degrees C. Aggressiveness varied among the pathogens, with P. digitatum and A. alternata being the most aggressive, followed by G. citri-aurantii and P. expansum, while P. italicum was the least aggressive. This study establishes the first pathogenic profile for kumquat decay, providing a framework for evidence-based postharvest management. The demonstrated efficiency of SCoT 32 and iPBS 2395 markers highlights their value as powerful, rapid, and cost-effective tools for pathogen surveillance and taxonomic resolution in postharvest pathology.