Morphological and physiological responses of two contrasting Malus species to exogenous abscisic acid application

This study characterized morphological and physiological responses of two Malus species to exogenous abscisic acid (ABA) application under both well-watered and drought-stressed conditions. Exogenous ABA was sprayed onto the leaves of potted 1-year-old seedlings of M. sieversii and M. hupehensis, originated from regions with low annual rainfall and high annual rainfall, respectively. The results demonstrated that exogenous ABA application significantly decreased height growth (H), total biomass (TB), total leaf area (LA), net photosynthesis (A) and stomatal conductance (g(s)), and significantly increased root/shoot ratio (RS), specific leaf area (SLA), endogenous ABA concentration, water use efficiency (WUE) and carbon isotope composition (delta C-13) under both well-watered and drought-stressed conditions. However, distinct interspecific differences were found in ABA-induced morphological and physiological responses. Compared with M. hupehensis, M. sieversii was more responsive to exogenous ABA application, resulting in larger decreases in H, LA, A and g(s), and larger increases in RS, SLA, WUEL, WUEi, ABA and delta C-13. These results suggest strong evidence for different maintenance of fitness under stressful conditions between species of Malus. In addition, application of exogenous ABA appears to enhance the tolerance of two Malus species to drought-stress.