Seed germination and viability in two African Acacia species growing under different water stress levels

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.