Adaptive genetic variation in water-use efficiency and gum yield in Acacia senegal provenances grown on clay soil in the Blue Nile region, Sudan

The genetic variation in shoot growth, water-use efficiency (as assessed by δ13C) and gum production was compared among eight Acacia senegal provenances originating from contrasting conditions of the gum arabic belt in central Sudan. The experimental site was in the clay plain region. Carbon isotope ratios were obtained from leaves and branch wood samples of the dissimilar A. senegal provenances. The clay provenances were distinctly superior to the sand provenances in all traits studied but especially in basal diameter and crown width, reflecting their adaptation to the environment. Values of δ13C were less negative in the sand group compared to the clay both in leaves and in branch wood. This suggests that sand provenances displayed conservative water use and high drought tolerance. Of the clay provenances, the local one displayed a high negative δ13C value, which indicates less conservative water use that results in high productivity at this particular clay-soil site. Water use appears to correspond to the environmental conditions prevailing at collection sites for these provenances. Results suggest that A. senegal provenances in the clay part of the gum belt are adapted for fast growth rate and high biomass and gum productivity as compared with the provenances from the sand regions: a negative correlation was found between tree gum yield and δ13C. The variation in water use and gum production was greater among provenance groups than within them, suggesting that selection among rather than within provenances would result in distinct genetic gain in gum yield.