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.