Pathogenicity and Cultural Variability of Botrytis aclada Causing Neck Rot on Onion in Post-Harvest Storage

Abstract

Post-harvest neck rot symptoms observed in stored onion (Allium cepa L.) bulbs were investigated to determine the pathogenicity and cultural variability of Botrytis aclada. Diseased bulbs collected from storage facilities exhibited soft decay at the neck region, water-soaked lesions, and progressive tissue collapse accompanied by gray sporulation under high humidity conditions. Fungal isolates obtained from infected tissues produced slow-growing colonies with gray to dark mycelium on potato dextrose agar, with abundant conidiophores and branched conidial clusters characteristic of Botrytis species. Pathogenicity assays conducted on healthy onion bulbs under controlled storage conditions successfully reproduced neck rot symptoms, confirming the virulence of the pathogen and fulfilling Koch’s postulates. Cultural studies revealed significant variability among isolates in colony growth rate, mycelial texture, pigmentation, and sporulation intensity, indicating the presence of phenotypically diverse populations. Temperature strongly influenced fungal growth, with optimal development observed under cool and humid conditions typical of storage environments. Molecular confirmation using ITS rDNA sequencing identified isolates as Botrytis aclada, showing high similarity with reference sequences from global databases. Phylogenetic analysis placed all isolates within a well-supported B. aclada clade, with limited but detectable genetic variation among regional populations. The study highlights the epidemiological importance of B. aclada as a major post-harvest pathogen of onion and emphasizes the role of storage conditions in disease development and spread.