Rapid Hydroponic Screening of Crops for Aluminium Tolerance

Aluminium toxicity is a major crop production constraint, particularly in acid tropical soils. The toxicity is aggravated when pH falls below 5.5 since toxic monomeric Al species get solubilized. The screening of Al tolerance intrinsically depends on culture medium, with a nutrient solution having pH of 4.5 being recommended. Hydroponic experiment was carried out at Jomo Kenyatta University of Agriculture and Technology in February 2010 to investigate maize (Zea mays), garden pea (Pisum sativum), bean (Phaseolus vulgaris L) and cucumber (Cucumis sativus) tolerance to elevated Al in the rhizosphere during the early plant growth stages. We hypothesized existence of genotypic differences in tolerance to Al stress. The above plants constituted the main plots and subplots consisted of 3 levels of monomeric aluminium species (0, 50 and 100M) supplied as AlCl3. The plants were cultivated for 7d in full strength solution after transplant from peat/perlite mixture. On application of Al, the pH of the incubation medium was adjusted to 4.5. Based on morphological differences, putative aluminium resistant crop genotypes were identified. Increasing Al concentration to 100M significantly affected root elongation rates, shoot DM, root DM and root/shoot ratios of cucumber, bean and garden pea but marginally affecting maize and the trend was same for root/shoot ratio. The 50M Al supply did not seem to have clear inhibitive effect as expected and in some instances eliciting promotive growth. The experiment reveals genotypic variation in plant genotypes in Al tolerance that can be exploited for target breeding in acid soils. The root elongation was the single most significant index in ranking the genotypes against Al tolerance. We also conclude that simple nutrient solution can be effectively used for screening crops for Al tolerance.