ARS | Publication request: Stem-end defect in chipping potatoes (Solanumtuberosum L.) as influenced by mild environmental stresses

Submitted to: American Journal of Potato Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: July 20, 2012
Publication Date: August 15, 2012
Citation: Wang, Y., Bussan, A.J., Bethke, P.C. 2012. Stem-end defect in chipping potatoes (Solanumtuberosum L.) as influenced by mild environmental stresses . American Journal of Potato Research. 89(5):392-399.

Interpretive Summary: Tubers used by the potato processing industry must meet rigorous quality standards. Tuber quality defects that result in blemishes on chips are undesirable to consumers, and may result in rejection of tubers at processing facilities. Stem-end chip defect is a serious quality concern for chipping potatoes that is characterized by a dark-colored region close to the point where the tuber was attached to the rest of the plant. Stem-end chip defect occurs erratically and with varying severity across years and locations. The erratic occurrence of stem-end chip defect in production fields and during post-harvest storage has made it difficult to conduct research on this important quality defect. Identifying environmental conditions or cultural management practices that cause defect formation would improve the ability of industry to anticipate when defects are likely to occur, and to select for varieties that are resistant to defect formation. Being able to create defects experimentally would enable more efficient research on defect development and changes in defects during tuber storage. A research project was conducted in temperature-controlled greenhouses with the objective of identifying the causes of stem-end chip defects. The influence of moderate water deficit, alone or in combination with elevated daytime temperature during early or late tuber bulking, immaturity of plants at harvest, and post harvest storage of tubers on the incidence, severity and underlying biochemistry of stem-end chip defects were investigated. Most of those treatments were not sufficient to cause an increase in either the incidence or severity of stem-end chip defects. The only exception to this was for temperature in one year, where the percentage of severe defects increased from 6% to 14% when plants were treated with 30°C daytime temperature. Elevated concentrations of the sugar glucose at the tuber stem end were associated with more severe stem-end chip defects. Greater activity of the glucose-forming enzyme acid invertase was observed in tubers that had the most severe stem-end chip defects. These data suggest strongly that acid invertase activity is up regulated at the tuber stem end, and the higher rates of activity give rise to more severe defects through the production of excess sugars. This finding provides an opening for further studies into the underlying causes of stem-end chip defect.

Technical Abstract: Global consumption of potato (Solanum tuberosum, L.) continues to shift from fresh potatoes to value-added processed food products such as potato chips. One serious tuber quality defect of chipping potatoes is stem-end chip defect, which results in chips with dark vasculature and adjacent tissues at the tuber stem end after frying. The cause of stem-end chip defect is not known, but environmental stress is thought to play a role. The influence of moderate water stress, alone or in combination with moderate heat stress, as well as tuber maturity at harvest on the incidence and severity of stem-end chip defects was investigated. Of the treatments imposed in controlled environment greenhouses, only temperature stress in one of two years significantly changed the occurrence of stem-end chip defects. Biochemical analyses showed that more severe defects were associated with increased amounts of tuber stem-end glucose and increased stem-end acid invertase activity. We conclude that moderate environmental stresses and chemical immaturity of tubers at harvest are not the direct causes of stem-end chip defect.