Methodologies and Traits for Evaluating the Salt Tolerance in Diploid Potato Clones

Efforts to incorporate the salt stress tolerance expressed by certain wild diploid potato species into improvement programs for cultivated tetraploid potatoes are hampered by a lack of quick, efficient and representative salt stress tolerance screening methods capable of evaluating diverse potato genotypes. This study developed screening methods and evaluated phenotypic and physiological responses as indicators of salt tolerance in diploid potato clones (Solanum tuberosum L. x wild relatives) utilizing a hydroponic sand-based system. When diploid clones known to vary in their salt tolerance were treated at tuber initiation with salinities ranging from 0 to 300 mM NaCl for 30 days, treatment with 100–150 mM NaCl allowed for rapid differentiation between salt tolerant and sensitive clones. Differences in relative salt tolerance were more clearly illustrated by changes in shoot growth and water content than by changes in shoot or root dry weights. Salt tolerances of 22 diploid potato clones were then evaluated by exposure to 100 to 150 mM NaCl stress for 28 days beginning at tuber initiation. Cluster analysis was used to segregate the clones into discrete groups based on the relative similarity of their responses to salt stress. Eight clones were subsequently selected to reflect a range in salinity tolerance and maturity. The eight clones were exposed to salinity stress for the reduced stress period of 7 days and then grown through to maturity. The 7 days stress period still allowed differentiation of tolerant versus sensitive clones. Growth index in both the 30 and 7 days salt stress trials was a good predictor of absolute tuber yield but not tuber yield tolerance to salt stress (tuber yield under stress / tuber yield under non-stress conditions). Tuber yield tolerance to salt stress was positively correlated with time to maturity. When the genotypes were ranked based on cluster analysis of a range of readily measured phenotypic and physiological responses to salt stress, the ranking was effective at predicting the relative impact of a salt stress event on tuber yield at maturity. While growth index may be a useful initial rapid selection tool, maturity and cluster analysis based on readily measured phenotypic characteristics were more effective in predicting relative yield tolerance to salt stress than individual phenotypic or physiological responses.