CONTROL OF ORGANOGENESIS "IN VITRO" OF PISTACIA ATLANTICA DESF. ROOTSTOCK.
Studies were carried through "in vitro" organ and tissue cultures on diverse species and cultivars of this genus (6) (5) (1) (3) (4) (12) (11) (8) (7) (10) (13) and in spite of these studies, problems found have been numerous: browning exudate; apical necrosis; shoot development and shoot proliferation with badly formed leaves and so on.
The aim of our work was to avoid in certain way, some of the problems found during "in vitro" establishment of the Pistacia atlantica Desf. (Almácigo) specie and one of them was the shoot-tip necrosis.
Apical and axillary buds explants were collected from young mother plants. The Almácigo medium was used (Mederos and Rodriguez; 1990). In this medium the calcium level was modified by addition of calcium nitrate in the culture medium. All cultures were incubated at 24°C under 16 hr photoperiod (30 μExm-2xs-1). The experiments were repeated twice. The effects of twelve levels of calcium nitrate -between 0.0 and 13.6 mEq/1- 0n the development and behaviour of the Pistacia atlantica Desf. shoots were studied under "in vitro" conditions.
The results showed that the required levels of calcium ions was 1.70 mEq/1 because enhanced the development of shoots. The increase in the culture medium of calcium level between 3.4 mEq/1 and 10.2 mEq/1 produced shoots vigorous, present long internodes and aquire a good length, however, the causes for which we have eliminated such calcium levels are the following: Presence of browning exudates which was directly proporcional to the concentrations of calcium ions; abscission of the leaves; shoot-tip necrosis which progressively and quickly advences in a basipetal sense. On the other hand, the toxic level of the calcium for development of the shoots were 11.85 mEq/1 and 13.55 mEq/1 respectively. These studies indicate that the presence of high levels of calcium ions supplemented in the Almácigo culture medium causes the contrary to that observed in other species (14) (9) (2). These elevated concentrations also seem to facilitate the appearance