Genetic diversity among populations of the xerophytic tree species Balanites aegyptiaca and its morpho-physiological responses to water deficiency

Water deficit negatively affects crop development and productivity. With decreasing rainfall and shortage of arable land, there is a demand for alternative drought-tolerant species for use on non-arable land. The tree species Balanites aegyptiaca is considered as drought tolerant and a potential source of many secondary metabolites. The oil-containing seeds may also be used as biofuel. Genetic diversity was investigated amongst the B. aegyptiaca collected from different geographical regions using amplified fragment length polymorphism (AFLP) and the relationship among geographical distribution and genetic diversity was determined. Plants were grown from seedlings collected at 12 locations from 11 provenances. AFLP produced 510 bands of which 477 (93.5%) were polymorphic. Cluster and principal component analyses indicated that individual samples of B. aegyptiaca were distributed in 3 main clades and that the provenance El-Kharga represented a single clade. Several key morpho-physiological responses to water stress were examined to evaluate drought stress tolerance and to compare respective stress responses among different provenances under greenhouse conditions. Severe drought stress decreased biomass parameters in all genotypes. However, B. aegyptiaca provenances also differed in their adaptive responses to water shortage. By appropriate grouping of 2 or 3 response factors, the effects of water deficit on the various provenances could readily be distinguished. Provenance El-Kharga showed the smallest amount of biomass reduction under severe drought stress and retained the highest leaf water content.   Key words: Amplified fragment length polymorphism (AFLP), Balanites aegyptiaca, biometrical growth parameters, drought tolerance, stomatal conductance.