Physiological changes and growth of micropropagated chile ancho pepper plantlets during acclimatization and post-acclimatization

Little is known about physiological changes that occur with micropropagated chile ancho pepper (Capsicum annuum L. cv. San Luis) plantlets during acclimatization. Plantlets were transferred to ex vitro conditions to study selected physiological changes and growth performance during acclimatization and post-acclimatization. The physiology of the plantlets was characterized by measuring leaf gas exchange and water status. Plant growth was determined by assessing plant height, leaf number, total leaf area, relative growth rate (RGR), and leaf, root, and stem dry matter (DM). Chile pepper plantlets became acclimatized within 6 days after transplantation. During this period, physiological adjustments occurred, which were critical for plantlet survival. After initial ex vitro transplanting, plantlets experienced water deficit [leaf wilting and reduced relative water content (RWC)], which corresponded with reduced stomatal conductance (gs) and transpiration (E), and an increase in stomatal resistance (rs). Thus, leaf stomata that developed in vitro were functional ex vitro. Because of this stomatal control, plantlets minimized transplant shock, recovered and survived. Prior to transplanting, plantlets were photomixotrophic, as indicated by low photosynthetic rates (A). During acclimatization, RWC, gs, E, and A were significantly lower two days after transplanting. However, within 6 days after transplanting, plantlets recovered and became photoautotrophic – attaining high A, gs, and E. Water use efficiency was initially low during the first days after transplanting, but increased dramatically at the end of the acclimatization period in part due to increased A. The stabilization and improvement of plantlet water status and gas exchange during acclimatization and post-acclimatization closely correlated with increased plantlet growth.