Evaluation of Cercospora leaf spot on impacts on postharvest rot susceptibility and storage rot effects on sugar beet respiration.
In Michigan, sugar beets (Beta vulgaris) are stored for up to 200 days post-harvest. During storage, sugar content is reduced due to rot and regular energy use from respiration. Cercospora leaf spot (CLS) is hypothesized to be a predisposing factor for storage losses, specifically for increased storage rot. However, previous studies have presented conflicting evidence of this interaction and the effects of CLS remain unclear for specific storage pathogens. To investigate the impact of CLS on fungal storage rot, post-harvest symptom development was evaluated in beets with relatively high or low in-season CLS severity. At three timepoints during storage, roots of each CLS level were inoculated with Fusarium graminearum, Botrytis cinerea, Penicillium vulpinum, or Geotrichum candidum and symptoms assessed after 7 days. There were no significant differences between storage rot susceptibility to any of the tested pathogens in beets, regardless of CLS level, at any timepoint in any year (P > 0.05). The effect of CLS and storage rot inoculation on root respiration rate was also evaluated in respirometry chambers in 2021. Preliminary data shows a significant increase in respiration rate in beets inoculated with pathogens compared to control (P <0.05), as well as variation among respiration rates between the storage pathogens. Studies are ongoing and will increase understanding of factors contributing to potential storage losses. Such knowledge could allow targeted disease management for high impact disease and lead to improved sugar retention and related profit for sugar producers.