Variation in Drought Tolerance and Survival among Three Provenances of Acacia tortilis Subspecies Radinana and Subspecies Spirocarpa Seedlings

The aim of this study was to investigate inter-specific variation in drought tolerance and survival among three provenances of Acacia tortilis subspecies Raddiana and subspecies Spirocarpa under water stress. The seeds were collected from White Nile (Elgetiana), Kassala (Halfa Elgadida) and River Nile (Shandi) states, where the association of the two subspecies occurs in their natural habitats. The seeds of each subspecies per each provenance were sown under three irrigation frequencies. Relative growth rate, relative water contents, biomass production and mortality rates were measured. At the end of growth measurements water was totally with held from all the seedlings and mortality was counted at one week interval. The results revealed significant irrigation treatment and subspecies effects in relative growth rate, leaf relative water content and seedlings mortality, where no significant differences exist between the provenances.Water stress increased relative water content and decreased relative growth rate and mortality. Drought preconditioning increased seedlings survival during the final dry-down compared to well-watered. Seedlings that had been preconditioned to drought survived 14 days longer than those had been well watered. The high similarity between provenances might reflect adaptation to near similar environmental conditions, whereas the variation within subspecies could be due to genetic differentiation resulting from minor environmental differences or to individual tree differences within provenances.