Effect of Vapor Gard and Triisopropanolamine on Boron Absorption by Kiwifruit Plants

Abstract

Kiwifruit plants were grown in sand/perlite mixtures and irrigated with nutrient solutions containing 0.025, 0.2, and 0.5 mM boron (B) combined with 0, 1.5, 3, and 6 mM triisopropanolamine (TIPA). Growth parameters and B concentration of various plant parts were investigated. By increasing TIPA concentration from 1.5 to 6 mM in solutions containing 0.2 mM B, the concentration of leaf B decreased. However, even the highest TIPA concentration did not decrease B concentration of leaves when its concentration in solution was 0.5 mM. The accumulation of B in leaves and its relatively low concentration in roots and shoots indicates that kiwifruit lacks a B exclusion mechanism. Furthermore, the occurrence of higher B concentrations in mature leaves in comparison to younger ones is evidence of phloem B immobility of kiwifruit plants. In another experiment, the nutrient solutions contained three B levels (0.025, 0.1, 0.2 mM) and plants sprayed with the antitranspirant compound “vapor gard” with aqueous solutions containing 5, 10, and 15% “vapor gard.” Moderate B toxicity symptoms were exhibited by plants irrigated with solutions containing 0.1 mM B. However, when plants sprayed with the antitranspirant compound no visual symptoms of B toxicity were exhibited. Severe B toxicity symptoms were exhibited by plants irrigated with solutions containing 0.2 mM B even when they were sprayed with “vapor gard.” As the concentration of “vapor gard” increased from 5 to 15%, the shoot height of plants, the mean shoot fresh weight and the mean leaf fresh weight decreased for all B treatments. When plants irrigated with solutions containing 0.1 and 0.2 mM B, the spray with “vapor gard” (10 and 15%) resulted in a decrease of B concentration of leaves.