Pathogenicity of <i>Fusarium</i> Species Associated with Potato Dry Rot in the Pacific Northwest of the United States

Fusarium dry rot is a ubiquitous disease of potato affecting tubers in storage and at planting. A greater understanding of the current <i>Fusarium</i> 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 <i>Fusarium</i> isolates recovered from PNW tuber samples were confirmed using molecular phylogenetic analyses based on partial sequences of <i>tef</i> and <i>pho</i> loci. Of the 20 species recovered, <i>F. sambucinum</i> was the most prevalent (44.6%), followed by <i>F. oxysporum</i> (13.8%). Selected isolates were tested for pathogenicity to potato tubers. Pathogenicity was confirmed for 14 species of <i>Fusarium</i>, including seven species not previously reported as Fusarium dry rot pathogens in the region. On potato 'Russet Burbank' (RB), inoculation with isolates of <i>F</i>. <i>sambucinum</i> resulted in the largest lesions (19.5 to 27.7 cm²), followed by isolates of <i>F. avenaceum</i>, <i>F. cerealis</i>, <i>F. culmorum</i>, <i>F. flocciferum</i>, <i>F. graminearum</i>, <i>F. oxysporum</i>, <i>F. redolens</i>, <i>F. sporotrichioides</i>, and <i>F. venenatum</i> (2.0 to 13.1 cm²). Inoculation with <i>F. acuminatum</i>, <i>F. equiseti</i>, <i>F. solani</i>, and <i>F. stercicola</i> resulted in the smallest lesions (0.1 to <2.0 cm²). An isolate of <i>F. redolens</i> 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 <i>Fusarium</i> species pathogenic to potato in the PNW is greater than previously reported. Management strategies should consider potato variety, pathogen species, and isolate aggressiveness.