Effects of agar concentration on water status and growth of rose plants cultured in vitro

Abstract

Rose (Rose hybrida cv. Madame G. Delbard) was micropropagated in vitro on agar at varying concentrations: 0, 4, 5.5, 6, 7.5, 8, 9 and 15 g l−1. Water status of the culture medium, leaf water potential, plant growth and propagation rate were investigated.Water potential of the medium was lincar function of agar concentration, and gel strength increased linearly from zero as agar concentration increased from 5 to 15 g l−1.Except for liquid medium, where shoot proliferation (total shoot number) was imparied by vitrification, fresh and dry weights and unmber of tatal shoots decreased linearly with increasing agar concentration. At low agar concentration, where water potential of the gelled medium was high, only few among numerous shoots that had attained a length of >0.3 cm were usable. Number of usable (elongated) shoots was significanly higher at a moderate level of agar, namely 7.5 g l−1. This can be explained in terms of the antagonistic actions of cytokinin and water on shoot elongation.At low agar concentration, leaf water potential and absolute water content were high. At high agar concentration, under gel water deficit, leaf water potential and absolute water content were low but an osmotic adjustment maintained turgor pressure. At moderate agar concentration, when the number of usable shoots was high, lower leaf turgor was found.