The role of abscisic acid in controlling leaf water loss, survival and growth of micropropagated Tagetes erecta plants when transferred directly to the field

Plants of Tagetes erecta L. (marigold) cultivated in vitro in ventilated co ntainers exhibited greater control of leaf water loss and increased surviva l in the field than plants cultivated in sealed containers. Increased field survival of plants cultivated in ventilated containers was attributed to h igher levels of endogenous abscisic acid (ABA). Therefore, ABA was supplied exogenously to plants in sealed or ventilated containers by adding ABA (10 (-6), 10(-5), 10(-4) M) to the in vitro culture media in order to evaluate control of leaf water loss, growth and field survival. The addition of 10(- 4) M ABA to the culture media in sealed containers produced plants that had similar control of leaf water loss and were morphologically similar to pla nts cultivated in ventilated containers without the addition of ABA. Field survival of 10(-4) M ABA plants (75%) was increased compared to plants cult ivated in sealed containers without ABA (31%), with survival being closer t o that of plants cultivated in ventilated containers (90-100%). Plants cult ivated with 10(-4) M ABA (sealed and ventilated) also exhibited increased p lant vigour and leaf area in the field compared to plants cultivated withou t ABA. The results suggest that the limited field survival and growth of pl ants cultured in vitro are related to the limited ABA concentrations they a ccumulate while in vitro. Consequently, conditions that increase the endoge nous ABA concentrations of in vitro plants (like Ventilation or ABA additio n to the medium) would improve the control of leaf water loss, field surviv al and plant vigour.