The method described herein permitted production of three to four micropropagules of Acacia Senegal from one uninodal explant. The explants were taken from plants produced either in a sterile environment or during four years in a greenhouse. Zeatin or 6-benzylaminopurine (BAP) were mixed, at different concentrations, with Murashige and Skoog's medium (MS) of which the amount of macroelements was divided in half (MS mod.). At a concentration of 5.0×10(-5) M, zeatin produced a better multiplication rate after 60 d for the two types of plant stock than did BAP. A two stage process was necessary to obtain a rooting rate of the small cuttings close to 100%. The first stage, called induction, consisted of leaving the cuttings for 6 to 12 d on a Jordan's medium (JN) of which the amount of macroelements was reduced by half (JN mod.) and in which NAA at a concentration of 5.0×10(-5) M was added. The second stage, called root extension, required that the small cuttings be planted on this second hormone-free medium. Roots appeared after a few days. Acclimatization in a greenhouse occured with a survival rate of close to 100% when the rooted in vitro plants were transplanted to pots containing a mixture of vermiculite and top soil (1∶1; v/v).

In order to study and monitor rates of rooting, callusing and survival, small diameter stem cuttings (less than 0.4 cm) with eight nodes (12--14 cm long) were taken from trees in the field at different times of the year in tests with small batches of cuttings. Among the four tested substrates, well drained crushed basalt powder placed on a bed of gravel was the best rooting medium. Rooting was generally poor or even non-existent with this type of cutting, but the presence of leaves both promoted rooting and significantly (using Chi square test) improved survival of the cutting. Four leaves were sufficient to assure the necessary metabolic functions. Only stem cuttings collected during the rainy season gave roots and then, only when hormonal treatments were applied to the cuttings. 8%-IBA resulted in significantly better rooting than did 2%-IBA, 0.2%-NAA and I%-IAA. With 8%-IBA, the rate of rooting varied between 50 and 70% for leafy cuttings collected in the rainy season. Hormonal treatments had a significant effect on the survival rate of the stem cuttings during the two months observation period. Further investigations are being conducted with different types of cuttings.Resum& Des boutures de huit noeuds (12 fi 14 cm de long) et de faible diam6tre (inf6rieur 0.4 cm) ont ~t6 pr61ev6es au champ, sur des arbres adultes, h diverses p6riodes de l'ann6e en vue d'6tudier leurs taux d'enracinement, de formation de cals et de survie. La poudre de basalte concass6e sur lit de gravier, avec un bon drainage, s'est r6v616e comme le meilleur substrat. Avec ce type de bouture, la pr6sence de feuilles parait absolument indispensable pour obtenir un enracinement. Quatre feuilles sont suffisantes pour assurer le r61e trophique qui est probablement le leur. La n6o-formation de racines n'est apparue que sur les boutures pr61ev6es durant la saison des pluies. Sans traitement hormonal les boutures du type 6tudi6 n'ont donn6 aucun r6sultat. L'AIB-8% en poudre se r6vble meilleur que I'AIB-2%, I'ANA-0.2% et I'AIA-I%. Avec I'AIB-8%, les taux d'enracinement vont de 50 fi 70% si le substrat, I'hygrom6trie, la pr6sence de feuilles et la p6riode de pr~16vement sont convenables.

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Vegetative propagation of Acacia senegal is possible from branch fragments taken from the crown of mature trees (13 years old), without causing o rtet destruction.The most responsive planting stock is taken from cuttings 15 cm long (with 12 to 15 nodes) and a diameter of 10 _+ 6 mm (wood of 2 to 4 years old). With this material, the ablation of the leaves prior to planting is a factor which furthers development of the cutting's root system.The development of the root system is also highly influenced by the time at which the cutting is taken: results vary from 10% during the dry season to more than 70% during the rainy season (June-October).Cuttings can be taken from branches 50 cm long. It is thus possible to preserve the planting stock for 8 days in a continually humidified jute cloth and then to make the cuttings at the time of establishment in a nursery, without changing their rhizogenic aptitude.The cuttings show characteristics of maturity (slow growth, plagiotropy, fructification). It is nevertheless possible to preserve the collected genotypes in the field, or better, in planting pots in the nursery, so as to further the process of physiologic rejuvenation with the aim of in vitro cloning. R6sumd

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