Pathogenicity of Fusarium Species Associated with Potato Dry Rot in the Pacific Northwest of the United States

Abstract

Fusarium dry rot is a ubiquitous disease of potato affecting tubers in storage and at planting. A greater understanding of the current Fusarium species composition associated with Fusarium dry rot in the Pacific Northwest (PNW) will aid in refinement of current management strategies. In this study, the identity of 327 single-spore Fusarium isolates recovered from PNW tuber samples were confirmed using molecular phylogenetic analyses based on partial sequences of tef and pho loci. Of the 20 species recovered, F. sambucinum was the most prevalent (44.6%), followed by F. oxysporum (13.8%). Selected isolates were tested for pathogenicity to potato tubers. Pathogenicity was confirmed for 14 species of Fusarium, including seven species not previously reported as Fusarium dry rot pathogens in the region. On potato ‘Russet Burbank’ (RB), inoculation with isolates of F. sambucinum resulted in the largest lesions (19.5 to 27.7 cm2), followed by isolates of F. avenaceum, F. cerealis, F. culmorum, F. flocciferum, F. graminearum, F. oxysporum, F. redolens, F. sporotrichioides, and F. venenatum (2.0 to 13.1 cm2). Inoculation with F. acuminatum, F. equiseti, F. solani, and F. stercicola resulted in the smallest lesions (0.1 to <2.0 cm2). An isolate of F. redolens caused lesions that were 5.7-fold larger on potato ‘Dark Red Norland’ compared with those on RB (13.1 and 2.6 cm2, respectively), indicating variety selection may play a role in managing Fusarium dry rot. Diversity of Fusarium species pathogenic to potato in the PNW is greater than previously reported. Management strategies should consider potato variety, pathogen species, and isolate aggressiveness.