Physiological and nutritional responses in two highbush blueberry cultivars exposed to deficiency and excess of boron

Boron (B) is an essential micronutrient required for physiological and biochemical processes in fruit crops such as highbush blueberry (Vaccinium corymbosum L.), well adapted species to acidic soils (pH(water) <= 5.5) with relatively low B availability. However, an optimal range of B supplies is quite narrow, particularly among cultivars, making it easy to under-or over-fertilize which could lead to boron toxicity. Under controlled conditions, cultivars Brigitta and Legacy were grown in a peat moss substrate (pH 4.5) with five B concentrations (0, 50, 200, 400 and 800 mu M). Plant biomass, nutrient concentration, water potential (Psi(leaf)), oxidative stress and antioxidant activity were determined at 30 d. Concentrations of 400 and 800 mu M B reduced shoot and root growth in both cultivars, and 800 mu M B decreased. leaf in Legacy and significantly increased it in Brigitta. Boron applied at 400 aeM resulted in the highest B accumulation in leaves of Brigitta (5-fold) and Legacy (2-fold), whereas Brigitta roots showed up to 60% increased B accumulation in comparison with 50 mu M B, respectively. High B caused more severe oxidative stress in leaves of Legacy than B deficiency. The antioxidant activity was increased from 50 to 400 mu M B in both cultivars. Boron added at 400 and 800 mu M impaired physiological and biochemical performance probably due to toxicity, demonstrating that highbush blueberry in a genotype-dependent manner has relatively low B requirement.