Differential Tolerance and Phenolic Leaf Profile in Response to Boron Supply in Two Highbush Blueberry Genotypes

Highbush blueberry (Vaccinium corymbosum L.) is beneficial for human health due to its bioactive properties. Agronomic management includes boron (B) addition to promote its growth and development. We aimed to provide new insights into the effects of B supply on the phenolic profile and antioxidative capacity in the leaves of two common cultivars, Brigitta and Legacy. Seedlings of Brigitta and Legacy were supplied with different B concentrations (0–50 mg B L−1). After 30 days, leaf biomass and B content, the activity of phenylalanine-ammonia-lyase (PAL, EC 4.3.1.24), the phenolic profile, and radical scavenging activity of methanolic extracts (oxygen radical absorbance capacity (ORAC), reducing 2,2-diphenyl-1-picrylhydrazyl (DPPH) and ferric reducing-antioxidant power (FRAP)) were analyzed. Tolerance to B was assessed by the lipid peroxidation level and superoxide dismutase (SOD, EC 1.15.1.1) activity. Leaf biomass in cultivars increased at 3 mg B L−1, while Legacy was more sensitive to higher B treatments than Brigitta, which was evidenced by increased lipid peroxidation and decreased SOD activity. Boron-induced inhibition of PAL activity was higher in Legacy. Cultivar-specific differences observed in hydroxycinnamic, flavonoid, and anthocyanin profiles of leaf extracts were related to radical scavenging capacities. The results indicate different B requirements in the two blueberry genotypes, which should be considered before B application to obtain an optimal antioxidant composition. Boron supply increased the accumulation of flavonoids in Brigitta and hydroxycinnamates in Legacy. Higher tolerance to excess B in Brigitta may be related to higher antioxidative capacity and SOD activity than Legacy.