Assessment of tolerance to Aluminum toxicity in olive (Olea europaea) based on root growth and organic acid Al3+ exclusion mechanism

摘要

Aluminum toxicity is a major agricultural problem at low pH that inhibits the root growth and plant development. Therefore, selecting cultivars with Aluminum (Al) tolerance will be crucial step for the breeding programs. This work was done with the objective of evaluating the Al tolerance of six principal olive genotypes: ‘MGSASC315’; ‘Barnea’; ‘Leccine’; ‘CLO0025’; ‘Coratina’ and ‘Mission’ based on relative root growth, organic acid exudation, and root apex hematoxylin staining analysis. For root growth and hematoxylin staining, the experiment was laid on 4 x 6 factorial (4 doses of AlCl3 (0, 250, 500 and 1000 μM), 6 genotypes of olive) in hydroponic solution under greenhouse condition. The root growth was measured for five consecutive weeks in a week interval. The organic acid exudation was evaluated after 24 and 48h exposure for Al in solution containing 0, 100, 200 and 400 μM of AlCl3. The 1000 μM of AlCl3 severely inhibited the root development of olive genotypes while 250 and 500 μM AlCl3 produced small damage when compared to plantlets grown in the control solution. The analysis of organic acid exudation after 24 and 48h exposure to Al3+ showed citric acid involved on Al tolerance mechanism in olive, whereas malate and oxalic acid did not. Among the olive genotypes MGSASC315, Barnea and Leccine recorded high relative root growth and high citric acid exudation under Al stress that showed these genotypes are tolerant for Aluminum stress. The result also showed hematoxylin staining of the root apex of olive tree was not efficient in discriminating among control, 250 and 500 μM AlCl3 treatments within each genotype.