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

Abstract

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 7 locations] was assessed in 2018-19 and 2019-20. 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 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; averaged 31 to 32 mm of rot) followed by Penicillium spp. (P. expansum 14-22 mm, P. polonicum 14-16 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 since a number of the Cladosporium spp. are established to be associated with human clinical samples.