Identification of Allophoma zantedeschiae causing a root rot of sugar beet in Wyoming, USA

Root rot diseases of sugar beet cause significant monetary losses worldwide, including in the United States. Effective disease management relies on proper identification and characterization of the prevailing and emerging pathogens. In 2021, symptomatic sugar beet roots were received from Wyoming, USA, with dark brown to black lesions and internal necrosis. Pathogenic organisms were isolated, purified, and characterized following standard protocols. Four Phoma-like isolates were recovered and subjected to morphological characterization. The phylogenetic relationship was evaluated using multilocus analyses of the ITS, rpb2, and tub2 regions. The pathogenicity test was performed on sugar beet roots, demonstrating the pathogen’s virulence. Based on morphological evaluation and molecular comparisons, the ascomycetous fungus Allophoma zantedeschiae was identified as the causal agent of the sugar beet root rot. Sugar beet growers and extension agents will benefit from these new findings to formulate effective disease management practices for this novel host–pathogen relationship.