Soil salinity affects over 20% of the worlds irrigated land. Potato (Solanum tuberosum L.), the most important vegetable crop worldwide, is relatively salt sensitive. However, relatively little work has been done on salt tolerance of the potato plant. This thesis investigated the methodology of treatment application and scion/rootstock effects on subsequent salt stress responses of four contrasting potato genotypes: Norland, 9506, 9120-05 [ABA-deficient mutant], and 9120-18 [ABA-normal sibling] grown hydroponically in sand. The effect of incremental salt stress were studied, using NaCl, CaCl2 and combined NaCl + CaCl2 pre- treatments as well as varying methods of ABA application with a specific focus on the role of rootstock and scion. Physiological responses of various potato genotypes to salt stress differed depending on how the salt stress was applied. An incremental salt stress regime was able to more effectively differentiate genotypes based on salt stress resistance and greater salt tolerance compared to a sudden salt shock. Generally, the ability to produce ABA was positively related to the degree of salt stress resistance, with higher ABA levels induced under incremental salt stress treatments compared to salt shock. The method of ABA application also had a marked effect on potato responses to salt stress. Slowly increasing concentrations of exogenous ABA maintained growth rates, enhanced root water content and induced more lateral shoot growth compared to a single ABA dose. The degree of salt tolerance induced by the grafted rootstock was primarily modulated by salt acclimation and was manifested in the scion as increased water content, stem diameter, dry matter accumulation, stomatal conductivity, and osmotic potential and was associated with reduced leaf necrosis. Using the salt-resistant 9506 line as a scion also significantly increased root fresh and dry weight and stem diameter as well as root water content of salt-sensitive ABA-deficient mutant rootstocks. Exogenous ABA appeared to enhance plant water status via the roots under salt stress beyond that of grafting alone. This was verified by more positive stomatal conductivity and greater upward water flow in ABA treated grafted and non-grafted plants as compared to the absence of upward water flow in non-treated grafted plants as measured via micro NMR imaging. NaCl pre-treatment produced greater salt stress resistance compared to pre-treatment with CaCl2 and was associated with a specific Na+ ion effect rather than a non-specific EC-dependent response. However, the presence of both ABA and CaCl2 appears to be necessary in order to enhance Na+ exclusion from the shoot and increases the K+/Na+ ratio.

Soil salinity affects over 20% of the worlds irrigated land. Potato (Solanum tuberosum L.), the most important vegetable crop worldwide, is relatively salt sensitive. However, relatively little work has been done on salt tolerance of the potato plant. This thesis investigated the methodology of treatment application and scion/rootstock effects on subsequent salt stress responses of four contrasting potato genotypes: Norland, 9506, 9120-05 [ABA-deficient mutant], and 9120-18 [ABA-normal sibling] grown hydroponically in sand. The effect of incremental salt stress were studied, using NaCl, CaCl2 and combined NaCl + CaCl2 pre- treatments as well as varying methods of ABA application with a specific focus on the role of rootstock and scion. Physiological responses of various potato genotypes to salt stress differed depending on how the salt stress was applied. An incremental salt stress regime was able to more effectively differentiate genotypes based on salt stress resistance and greater salt tolerance compared to a sudden salt shock. Generally, the ability to produce ABA was positively related to the degree of salt stress resistance, with higher ABA levels induced under incremental salt stress treatments compared to salt shock. The method of ABA application also had a marked effect on potato responses to salt stress. Slowly increasing concentrations of exogenous ABA maintained growth rates, enhanced root water content and induced more lateral shoot growth compared to a single ABA dose. The degree of salt tolerance induced by the grafted rootstock was primarily modulated by salt acclimation and was manifested in the scion as increased water content, stem diameter, dry matter accumulation, stomatal conductivity, and osmotic potential and was associated with reduced leaf necrosis. Using the salt-resistant 9506 line as a scion also significantly increased root fresh and dry weight and stem diameter as well as root water content of salt-sensitive ABA-deficient mutant rootstocks. Exogenous ABA appeared to enhance plant water status via the roots under salt stress beyond that of grafting alone. This was verified by more positive stomatal conductivity and greater upward water flow in ABA treated grafted and non-grafted plants as compared to the absence of upward water flow in non-treated grafted plants as measured via micro NMR imaging. NaCl pre-treatment produced greater salt stress resistance compared to pre-treatment with CaCl2 and was associated with a specific Na+ ion effect rather than a non-specific EC-dependent response. However, the presence of both ABA and CaCl2 appears to be necessary in order to enhance Na+ exclusion from the shoot and increases the K+/Na+ ratio.