Unraveling the Diversity of Fusarium Species Responsible for Potato Dry Rot in the San Luis Valley, Colorado

Potato dry rot is a serious postharvest disease that leads to substantial economic losses globally. This research explores the morphological and molecular diversity of Fusarium species associated with dry rot in the San Luis Valley (SLV), Colorado. Potato tubers exhibiting typical disease symptoms were collected during the 2023 and 2024 growing seasons. Fungal pathogens were isolated and characterized based on morphology and molecular markers, identifying four species: Fusarium oxysporum, F. sambucinum, F. clavum, and F. solani. Classification into four distinct groups was achieved through analyses of colony morphology, macroconidia, microconidia, and chlamydospore formation. Molecular identification using ITS, rpb2, and tef markers, coupled with sequencing and phylogenetic analysis, validated species identities and clustered isolates into well-defined clades. Growth rate assessments revealed significant interspecies variation, with F. sambucinum exhibiting the most rapid expansion. Pathogenicity tests on three potato cultivars indicated differing virulence levels, with F. solani inducing the most severe infections. This study is the first to report F. oxysporum, F. sambucinum, F. clavum, and F. solani as causal agents of Fusarium dry rot (FDR) in Colorado. Notably, F. clavum is documented for the first time in the U.S. as a pathogen associated with potato dry rot. The integration of molecular and classical diagnostic approaches emphasizes the genetic and morphological diversity of Fusarium species in the SLV and underscores their pathogenic potential. These insights lay the groundwork for future strategies aimed at mitigating FDR’s economic impact and safeguarding potato production in Colorado and beyond.