Growth and developmental responses of potato to osmotic stress under in vitro conditions.

The effect of mannitol on different genotypes of potato was studied in callus and plantlet culture. In vitro responses of five potato genotypes with well-known field behaviour to water deficit were analysed. After a 4-week-long cultivation on media containing mannitol up to 0.8 M, different morpho-physiological parameters were determined and statistically analysed. The useful concentration of mannitol for in vitro screening the osmotic tolerance of different genotypes depended on the type of culture; it was 0.4 M in plantlet-test and 0.8 M in callus-test. In callus-test the relative increase of callus mass was a useful parameter for determination of osmotic tolerance of genotypes at cellular level. In plantlet culture, stress index calculated from the rate of surviving in vitro shoots, number and length of roots per surviving explant and the rate of rooted explants were applicable to determine three groups according to the tolerant, medium tolerant and sensitive categories in agreement with the field behaviour of these genotypes. Under in vitro stress conditions we were able to distinguish the examined genotypes with different drought tolerance.