Severe preharvest drought elevates respiration and storage rot in postharvest sugarbeet roots

Authors: Fugate, Karen; LAFTA, ABBAS - North Dakota State University; Eide, John; KHAN, MOHAMED - North Dakota State University; FINGER, FERNANDO - Universidade Federal De Vicosa

Submitted to: Journal of Agronomy and Crop Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/7/2024
Publication Date: 6/27/2024
Citation: Fugate, K.K., Lafta, A., Eide, J.D., Khan, M., Finger, F. 2024. Severe preharvest drought elevates respiration and storage rot in postharvest sugarbeet roots. Journal of Agronomy and Crop Science. 210. Article e12718. https://doi.org/10.1111/jac.12718.
DOI: https://doi.org/10.1111/jac.12718

Interpretive Summary: Sugarbeets are largely produced without irrigation, making drought inevitable when rainfall is insufficient. Whether drought conditions prior to harvest affect sugarbeet root storage losses is currently unknown. Research was conducted to determine the effect of drought conditions just prior to harvest on sugarbeet root respiration rate and susceptibility to storage rots since these two factors are primarily responsible for storage losses. Greenhouse grown plants were subjected to three levels of drought stress by discontinuing watering for 7, 14, or 21 d prior to harvest. These drought treatments caused different levels of stress to plants, with plants from these treatments displaying differences in leaf wilting, leaf and root water content, and ability to carry out photosynthesis and cool leaves by evaporative transpiration. Harvested roots obtained from droughted plants were stored at 10°C and 95% relative humidity for up to 12 weeks. Root respiration rate, the major cause of sugar loss during storage, was significantly elevated by severe preharvest drought stress but was not majorly affected by lesser levels of drought stress. Severely drought stressed roots were also more susceptible to storage rots. Cellular membranes were damaged in severely drought stressed roots, and this damage is believed to be responsible for the observed increases in respiration rate and storage disease. Results suggest that severe drought stress prior to harvest significantly increases sugarbeet root storage losses. However, mild drought conditions prior to harvest likely have minimal effect on storage losses caused by root respiration or storage rots.

Technical Abstract: Sugarbeets are largely produced without irrigation, making drought stress inevitable when rainfall is insufficient. Whether drought stress impacts root storage, however, is currently unknown. Research was conducted to determine the effect of preharvest water stress on postharvest sugarbeet root respiration rate and susceptibility to storage rots since these traits are the primary determinants for sucrose loss and quality deterioration. Greenhouse grown plants were subjected to four levels of water deficit by discontinuing watering for 0, 7, 14, or 21 d prior to harvest. Plants receiving water restrictive treatments displayed physiological stress by leaf epinasty, reductions in net photosynthetic rate and leaf relative water content, and increases in leaf temperature, while the water content of roots harvested from these plants progressively decreased with the severity of the preharvest water deficit treatment. Harvested roots from all watering treatments were stored at 10 °C and 95 % relative humidity for up to 12 weeks and evaluated for respiration rate and susceptibility to storage rot. Root respiration rate during storage was inversely related to root water content at harvest by second-order equations, such that respiration was not significantly affected by minor reductions in root water content but increased exponentially for roots obtained from severely drought stressed plants with water contents at harvest of = 75 %. Similarly, roots with water contents = 75 % had elevated levels of electrolyte leakage, a measure of cellular membrane damage, and were more susceptible to dehydration and fungal infection during storage. In separate experiments, roots harvested from water-stressed plants were inoculated with Botrytis cinerea or Penicillium vulpinum, two causal agents for storage rots. In these experiments, preharvest water stress quantitatively increased root rot and qualitatively altered symptoms of their infection. Overall, these results demonstrate that severe preharvest drought stress is likely to significantly increase sugarbeet root storage losses caused by root respiration and storage rots, and that storage losses are likely to accelerate with time in storage. However, mild to moderate drought conditions prior to harvest are expected to have no or minimal effect on storage losses from root respiration or storage rots.