MORPHO-PHYSIOLOGICAL CHARACTERIZATION OF MAIZE SHOOTS SUBJECTED TO in vitro SELECTION UNDER OSMOTIC STRESS

In this study we examined the morpho-physiological responses of organogenic maize (Zea mays L.) shoots submitted to osmotic stress, simulated by the addition of polyethylene glycol (PEG-8000) to the culture media, across three recurrent selection cycles. The seeds of the lines L-13, L-14, L-16 and L-46, were germinated in vitro, and after 12 d the seedlings were dissected in 1 to 5 sections which were used as explants for the in vitro culture on a Murashige and Skoog solid medium added with agar 0.6 % (w/v), in order to induce organogenesis. Thereafter, shoots at the multiplication stage were exposed to osmotic stress in liquid medium added with PEG (10, 15 and 20 g L-1) during three cycles of selection (15 d each one). In the first experiment the morpho-physiological traits were determined on the first and third cycles of selection. In this essay significant effects of the interaction genotype x PEG were observed on height and number of leaves of shoots, as well as of genotype x cycle on leaf number and fresh weight, and of PEG x cycle on fresh weight. In the second experiment the shoot characteristics of the third cycle of selection were measured, finding a significant effect of genotype on shoot fresh and dry weight, and of PEG concentration on shoot fresh weight and water content. The interaction genotype x PEG had significant effects on the water potential, osmotic potential and osmotic adjustment of shoots. The best lines under stress were L-14 and L-16 because they displayed a greater osmotic adjustment and better morpho-physiological characteristics, thus indicating the viability of the in vitro selection for choosing better genotypes.