OSMOTIC POTENTIAL OF POTATOES SUBJECTED TO A SINGLE CYCLE OF WATER DEFICIT

Potato plants (Solanum tuberosum L.) of the cultivars Alpha, Cara, Blanka, Desiree and Idit, were exposed to a transient water deficit during tuber growth. Drought stress increased the concentration of solutes as assessed by refractometry and lowered the osmotic potentials as assessed by cryoscopy in both leaf and tuber tissues of the five cultivars. Differences among cultivars, as well as between leaf and tuber tissue of the same cultivar, could indicate variability of the soluble components contributing to the osmotic potential. Differences were noted in the response of the cultivars to the environment in terms of osmotic potentials. Essentially, two types of responses were identified: transient maintenance of lower osmotic potential for 24 - 48 h after stress relief; and inherently high concentration of solutes and low osmotic potential. The possible advantage of sensitivity to environmental changes is also considered.