Abstract

Acacia species are important in forestation programs and for producing non-timber forest products in arid and semiarid zones, but few studies have been carried out concerning the effects of drought in the germination in order to understand the regeneration process of the species. In this paper, we studied the morphology and the germination pattern under different water stress of Acacia senegal and Acacia seyal. Seeds were subjected to a water stress test for 45 days with four levels of water potential achieved by different concentrations of polyethylene glycol 6000. The germination process was studied by adjusting a Gompertz function, and obtaining related parameters of the curve (total germination, maximum germination rate and the t value corresponding to the inflection point of the curve, and time in reaching the, 50 and 90% of the total germination). The germination process in these species was rapid; there were no significant differences in any of the parameters of the curves depending on the stress treatment except for the total germination. Total germination was higher in A. senegal, and this species was more sensitive to the water availability than A. seyal, as deduced from the reaction norms in the two environments. The probability of germination was also modeled by a logistic regression, indicating the higher values for non stressed seeds. A consistent pattern is detected among the treatments. The results presented in this paper could be applied in forestation programs to improve germination in nurseries, and by incorporating the logistic models in more complete models describing the dynamic of regeneration under natural conditions.

Key words: Acacia, water stress, Logistic regression, germination, regeneration.