Pathogenicity and Molecular Diversity of Fusarium solani f. sp. cucurbitae Causing Crown Rot on Cucurbits

Abstract

Crown rot symptoms observed on cucurbit crops were investigated to determine the pathogenic potential and molecular diversity of Fusarium solani f. sp. cucurbitae. Field surveys across cucurbit-growing regions revealed progressive crown necrosis, plant wilting, vascular discoloration, and eventual plant collapse, particularly under warm and moist soil conditions. Fungal isolates recovered from infected crown tissues produced fast-growing, cottony colonies with white to cream mycelium that later developed bluish pigmentation. Microscopic observations revealed abundant microconidia, macroconidia, and chlamydospores, consistent with Fusarium solani complex characteristics. Pathogenicity assays conducted on healthy cucurbit seedlings under controlled conditions successfully reproduced crown rot symptoms, confirming virulence and fulfilling Koch’s postulates. Molecular characterization using ITS rDNA, TEF1-α, and RPB2 gene sequencing confirmed identity as F. solani f. sp. cucurbitae, with isolates clustering within a distinct clade of the Fusarium solani species complex. Phylogenetic analysis revealed moderate intraspecific variation among isolates from different geographic locations, suggesting genetic diversification possibly driven by host specialization and environmental adaptation. Observed sequence polymorphisms indicated the presence of multiple haplotypes within field populations, reflecting ongoing evolutionary dynamics in cucurbit production systems. Disease severity was positively correlated with soil moisture and temperature, highlighting the role of environmental conditions in epidemic development. The study emphasizes the increasing threat posed by F. solani f. sp. cucurbitae in cucurbit cultivation and underscores the importance of molecular diagnostics for accurate pathogen identification.