Incidence, Distribution, and Pathogenicity of Fungi Causing Root Rot in Idaho Long-Term Sugar Beet Storage Piles

Abstract

Fungal rots in sugar beet roots held in long-term storage can lead to considerable sucrose loss but the incidence and distribution of fungal rots inside sugar beet piles and pathogenicity for some species is poorly understood. Thus, Idaho sugar beet held in five outdoor and two indoor piles in 2014 and 2015 were investigated. The root surface area covered by fungal growth and discolored and healthy tissue were assessed in nine 1-m2 areas per pile using a stratified random sampling design. Pathogenicity was evaluated indoors via plug inoculation in 2015 and 2016. Botrytis cinerea covered more root surface area inside indoor piles (6 to 22%) than outdoor piles (0 to 3%) (P < 0.0001). No trends were evident for the Athelia-like sp. (0 to 15%) and Penicillium-type spp. (0 to 8%). Penicillium-type isolates comprised the following species: 60% Penicillium expansum, 34% P. cellarum, 3% P. polonicum, and 3% Talaromyces rugulosus. Trace levels (<1% of root surface) of other fungi, including Cladosporium and Fusarium spp., were evident on roots and in isolations. Based on sample location in a pile, there were no trends or differences; however, two outdoor piles (OVP1 and OVP2) had more healthy tissue (90 to 96%) than other piles (28 to 80%) (P < 0.0001). When the pathogenicity tests were analyzed by species, all were significantly different from each other (P < 0.0001), except for P. polonicum and P. expansum: B. cinerea (61 mm of rot), P. polonicum (36 mm), P. expansum (35 mm), P. cellarum (28 mm), Athelia-like sp. (21 mm), T. rugulosus (0 mm; not different from check), and noninoculated check (0 mm). The OVP1 and OVP2 piles had negligible fungal growth on roots after more than 120 days of storage under ambient conditions, which indicates that acceptable storage can be achieved over this time period through covering piles with tarps and cooling with ventilation pipe.