Micronutrients

Abstract

Broccoli (Brassica oleracea var. italica) plants grown in perlite were supplied with nutrient solutions containing 0.08, 0.41, 0.61, 0.81, 4.06, or 8.11 ppm boron. Plants grown in either low (0.08 ppm) or high (8.11 ppm) boron concentrations developed at slower rates than plants in the other boron concentrations. The reduction of stomatal conductance of boron‐deficient plants coincided with the early signs of leaf thickening and chlorosis. Chlorophyll levels and net photosynthetic (Pn) rates of plants in 0.08 ppm boron were significantly less than those in 0.41, 0.61, and 0.81 ppm boron. Heads produced by plants in 0.08 ppm had small, chlorotic buds, scale‐covered stalks, and high levels of total phenols and fiber.

Plants grown in high (4.06 and 8.11 ppm) boron concentrations had slightly chlorotic leaves throughout their life cycle and chlorotic leaf margins. Stomatal conductance and transpiration rate were not affected by boron toxicity. Although the chlorophyll content and Pn rates were lower for plants in 4.06 and 8.11 ppm boron than for those in 0.41, 0.61, and 0.81 ppm boron, head size was slightly larger. This finding suggests that high boron concentrations, which induce boron toxicity symptoms in leaves, may stimulate head development.

Key words:

• Brassica oleracea var. italica
• stomatal conductance
• photosynthesis
• plant nutrition
• fiber