Incidence, distribution, and pathogenicity of fungi causing root rot in Idaho long-term sugar beet storage piles

Authors: Strausbaugh, Carl

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/28/2018
Publication Date: 10/26/2018
Citation: Strausbaugh, C.A. 2018. Incidence, distribution, and pathogenicity of fungi causing root rot in Idaho long-term sugar beet storage piles. Plant Disease. 102(11):2296-2307. https://doi.org/10.1094/PDIS-03-18-0437-RE.
DOI: https://doi.org/10.1094/PDIS-03-18-0437-RE

Interpretive Summary: Fungal rots in sugar beet roots held in long-term storage can cause considerable sucrose loss leading to millions of dollars in lost revenue. 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 for fungal growth. The primary fungi found to be associated with rot in the piles were an Athelia-like sp., Botrytis cinerea, and Penicillium spp. (primarily P. expansum and P. cellarum). Two of these fungi, the Athelia-like sp. and P. cellarum, were first discovered by the ARS sugar beet research group in Kimberly, ID. The most pathogenic fungus was B. cinerea. The distribution of the fungi did not vary with location within the piles. However, some piles had less total fungal rot than others. The two indoor storage piles had the most rot, while the two outdoor vent piles located at the highest elevation had the least rot. These data show that physical management methods such as the use of tarped vent piles at higher elevation can allow for sugar beet roots to be held under ambient conditions for more than 100 days with very little damage from fungal rots.

Technical 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 was assessed in nine one-meter square areas per pile using a stratified random sampling design. Pathogenicity was evaluated indoors via plug inoculation in 2015 and 2016. Botrytis cinerea covered more (P <0.0001) of root surface area (6 to 22%) inside indoor piles than outdoor piles (0 to 3%). No trends were evident for the Athelia-like sp. (0 to 15%) and Penicillium-like spp. (0 to 8%). Penicillium-like isolates were comprised of the following species: 60% P. expansum, 34% P. cellarum, 3% P. polonicum, and 3% Talaromyces rugulosus. Trace levels (<1% of root surface) of other fungi including Cladosporium and Fusarium were evident on roots and in isolations. Based on sample location in a pile there were no trends or differences, but two outdoor piles (OVP1 and OVP2) had more (P <0.0001) healthy tissue (90-96%) than other piles (28-80%). When the pathogenicity tests were analyzed by species, all the species had significantly different (P <0.0001) levels of rot (in mm): B. cinerea (61), P. expansum (35), P. polonicum (31), P. cellarum (28), Athelia-like sp. (21), T. rugulosus (0), and non-inoculated check (0). The OVP1 and OVP2 piles had negligible fungal growth indicating proper storage can be achieved through tarped vent piles.