Incidence, Distribution, and Pathogenicity of Fungi Growing on Sugar Beet Roots on Top of Outdoor Piles in Idaho.

Sugar beet roots in Idaho are held under ambient conditions in outdoor storage piles, which can lead to fungal growth and rot and substantial sucrose loss. Thus, the incidence, distribution, and pathogenicity of fungi associated with fungal growth on the surface of sugar beet roots on top of outdoor piles was investigated. The surface fungal growth on sugar beet roots held on top of 14 Idaho outdoor piles (tarped ventilated [TV] piles and piles with no tarps or ventilation [NTV] at seven locations) was assessed in 2018 to 2019 and 2019 to 2020. Cladosporium spp. were the only fungi covering more than 1% of the root surface (2 to 48%) on top of NTV piles both years, with the most frequently isolated species being C. cladosporioides, C. macrocarpon, and C. subtilissimum in both years. On TV piles, Cladosporium spp. (13 to 60%) were also dominant, but Penicillium spp. (0 to 35%), an Athelia-like basidiomycete (0 to 2%), and Botrytis cinerea (0 to 2%) were also frequently present. In the plug assay to test pathogenicity, B. cinerea caused the most rot (P < 0.0001; average 31 to 32 mm of rot), followed by Penicillium spp. (P. expansum, 14 to 22 mm; P. polonicum, 14 to 16 mm; and P. cellarum, 10 mm). Although Cladosporium spp. caused little or no rot (0 to 2 mm), workers should be cautious on or around sugar beet piles because a number of the Cladosporium spp. are established to be associated with human clinical samples.