Water Stress Relations of the Potato Plant under Field Conditions¹

Potatoes ( Solanum tuberosum L.) grown in northern Maine are often subjected to extensive periods of drought. The objective of this study was to examine the physiological response of potatoes to soil water stress. Relative water content, leaf diffusive resistance, and tuber water potential of two potato varieties were measured under irrigated and nonirrigated conditions. There were pronounced differences in relative water content, leaf diffusive resistance, and tuber water potential as a result of irrigation. Relative water content (RWC) of plant leaves correlated well with soil water potential but poorly with leaf diffusive resistance. The two potato varieties differed in RWC when soil water potential was high. Tuber water potential correlated well with RWC and soil water potential. Similarity between tuber water potential and the RWC data suggested that the potato plant exhibits water stress when the soil water potential drops below −0.25 bar.