Boron toxicity in grapevine

Table grape production has recently become popular in arid and semiarid regions where conditions of salinity and excess boron (B) can be prevalent. This study addresses B toxicity in grapevine to define toxicity symptoms and evaluate growth, production, and B accumulation. The effect of excess B on grapevines (Vitis vinifera L. cv. Sugraone) was evaluated in a 4-year study in Israel's Jordan Valley. Vines were grown in 60-L perlite-filled containers and irrigated with complete nutrient solutions with four B concentrations: 0.03, 0.12, 0.21, and 0.31 mM. Vines were monitored for growth, yield, and B accumulation. Boron accumulation in leaves correlated with B toxicity symptoms that materialized as chlorosis and necrosis of leaves beginning at their margins, reduced leaf size, and reduced internodal distance between adjacent leaves. Boron accumulated in grapevine leaves linearly as a function of increased B in irrigation solution with time and with age of leaves. The highest B levels were found at the end of each season and in the oldest leaves. No long-term (multiyear) effect of exposure to B was observed because similar accumulation patterns and levels were found in each year of the experiment. Hence, consistently sampled diagnostic leaves and time of sampling for B analysis is seen to be critical to provide valid comparisons between vines or over time. Boron supply influenced vine growth. At low levels of B (0.03 mM), canopy development was restricted but trunk size was not. At high levels of B (0.21 and 0.31 mM), substantial visual symptoms of B toxicity were observed, and the rate of trunk growth was reduced, but pruning biomass was not influenced. Despite severe visual toxicity damage and reduced overall growth rates, commercial fruit yield of the vines remained unaffected by high environmental B levels.