Water control and survival of Ipomoea batatas grown photoautotrophically under forced ventilation and photomixotropically under natural ventilation

Water loss and its determining factors were compared in leaves of in vitro-grown sweet potato (Ipomoea batatas L. Lam, 'Beniazuma') plantlets cultured either photoautotrophically under forced ventilation (scaled-up vessel) or photomixotrophically under natural ventilation. Functional stomata, a greater amount of wax deposition on the leaves and smaller epidermal conductance were observed in plantlets cultured photoautotrophically under forced ventilation. When transplanted directly into soil in the greenhouse (without ex vitro hardening), plantlets grown photoautotrophically under forced ventilation survived better and grew faster. This was because they were better able to control transpiration and thus lost less water and showed no signs of wilting. In contrast, plantlets cultured under photomixotrophic conditions had open stomata which were not functional, a higher transpiration rate, and uncontrolled and rapid water loss immediately after transfer ex vitro. Thus, wilting and severe desiccation with irreversible tissue damage were observed in the leaves, which died within a few days. (C) 2000 Annals of Botany Company.