In vitro screening of several potato genotypes (29 cultivars and lines) to salinity stress was conducted. Single node explants were evaluated on the basis of their growth, microtuberization and biochemical analysis under different concentrations of salt (NaCl) stress. In most cases, increasing NaCl in the tissue culture medium resulted in reduction in plantlet growth, rooting and microtuberization potential in varying degrees, depending on the cultivar. Some genotypes such as Oceania, 97f-267 and Picasso produced higher number of microtuber under 150 mM NaCl than control. Generally, 97f-267, Oceania and Universa genotypes were ranked among salt tolerant, while Nicola, Safran, Diamant were ranked as moderate and Elodi, Triomph, Marabel, Bolista and 99-981 were ranked as salt sensitive based on morphological characters. Photosynthetic pigments decreased under salt stress, however, Universa and Safran maintained higher chlorophyll content under salt conditions (100 mM NaCl) comparing with control (0.0 mM NaCl) plantlets. Also, Universa and Safran accumulated more proline and free amino acids under stress treatment comparing with control, than other tested genotypes. The activities of antioxidant enzymes were different among potato genotypes. In this respect, Universa and Safran had higher catalase (CAT) activity under salt stress (100 mM NaCl) than control treatment (0.0 mM NaCl), however, superoxide dismutase (SOD) activity was not good indicator for salinity tolerance in the tested potato genotypes.

In vitro screening of several potato genotypes (27 cultivars and breeding lines) for agar-induced water stress was conducted. Single node explants were evaluated on the basis of their plantlet growth and microtuberization under different concentrations of agar (7-10 g/l). Increasing agar in the tissue culture medium resulted in reduction in plantlet growth, rooting and tuberization potential in varying degrees, depending on the cultivar. Under agar-induced water stress, Safran and Universa were generally among the ranked tolerant cvs; Nicola, Triomph and Agria as moderate; Diamant and Bolista as sensitive to drought. Photosynthetic pigment contents under agar-induced water stress were markedly decreased in most cvs tested. However, the cv. Universa showed larger decline in total chlorophyll than Diamant or Bolista. Biochemical analysis of potato plantlet indicated increase in free amino acids, proline and catalase (CAT) activities under water stress, while superoxide dismutase (SOD) was less than the control. Results also indicated that the free amino acids and CAT activity were positively correlated with the tolerance mechanism to water stress.