Abscisic acid added to the nutrient solution induces a water deficit-like response in Trifolium subterraneum

The response of subterranean clover (Trifolium subterraneum) to the addition of increasing concentrations of abscisic acid (ABA) in the nutrient solution (10^?3, 10^?2 and 10^?1 mol m^?3) was studied under growth room conditions. Six cultivars of contrasting yield capacity were compared. Plants were grown in Hoagland's solution until they had produced at least four fully developed leaves. ABA was then added and its effect on the fresh weight, leaf number and longest root length was determined, 1 day, 4 days, 7 days and 11 days after addition. The addition of ABA caused significant reductions in all the measured growth parameters, as well as a significant decrease in leaf water potential, which was dependent on the ABA concentration. The average growth reduction after 11 days under 10^?1 mol m^?3 ABA were within previously reported ranges for this crop under drought, in field conditions. The average leaf number, area of a fully developed leaf and the dry weight per plant of the six cultivars decreased by approximately 50%, whereas the root/shoot ratio increased by 80%. The variation and ranking for this treatment resembled closely those obtained for the same cultivars in field experiments. The cvs Clare, Nuba and Seaton Park, showed the best results under both control and ABA treated conditions. The correlation between the response to ABA in nutrient solution and previous water deficit studies raises the possibility of using this approach as an alternative way to quantify the drought sensitivity of subterranean clover cultivars.