Micronutrient Toxicity in Seed Geranium (Pelargonium × hortorum Bailey)

Seed geranium (Pelargonium × hortorum) micronutrient toxicity symptoms were induced by applying elevated levels of B, Cu, Fe, Mn, Mo, and Zn in fertilizer solution. Beginning at the 3-4 true leaf stage, seedling plants established in 11-cm (0.67-liter) pots containing peat-lite growing medium were fertilized at each irrigation for 5 weeks with solutions containing 0.25, 0.5, 1, 2, 3, 4, 5, and 6 m M plus the standard concentration of each micronutrient. The standard solution contained 20 µM B, 0.5 µM Cu, 10 µM Fe, 10 µM Mn, 0.5 µM Mo, and 4 µM Zn. All treatment solutions contained a fixed level of macronutrients. Visible foliar toxicity symptoms were produced when the nutrient solution contained 0.5 m M B, 0.5 mM Cu, 5 mM Fe, 1 mM Mn, 0.25 mM Mo, or 0.5 mM Zn. Reduction in dry matter yield was evident when 1 mM B, 2 mM Cu, 3 mM Fe, 2 mM Mn, 0.5 mM Mo, or 1 mM Zn was used in the fertilizer solution. Leaf chlorophyll contents decreased as Cu and Mn levels in the concentration range tested increased. Elevated levels of Fe increased tissue chlorophyll contents. The relationship between the nutrient solution and tissue concentrations of each of the six micronutrients was determined. A soil medium high in nutrient holding capacity does not usually require additional supply of micronutrient s when used for short-term crops such as bedding plants. Micronutrient fertiliza- tion, however, is essential for bedding plants grown in the soil-less root media , which are now extensively used in greenhouse crop production. Growers formulate micronutrients based on the Hoagland solution (Hoagland and Arnon, 1950), or use commer- cial fertilizers containing both macro- and micronutrients. Since plants require only minute quantities of these elements, a nutrient imbalance may occur when commercial fertilizers are used with water containing high levels of some micronutrients. Micronutri- ent deficiencies and toxicities have been reported for boron in chrysanthemum (Gogue and Sanderson, 1973), Easter lily (Marousky, 1981) and begonia (Elliot and Nelson, 1981; Nelson et al., 1979), for molybdenum in poinsettia (Hammer and Bailey, 1987), for manganese in Spathiphyllum (Broschat and Donselman, 1986), and for iron in Tolmiea (Smith, 1985). Such investigations are largely lacking in bedding plants. The objective of this study was to induce and characterize micronutrient toxicity symptoms of seed geraniums grown in a peat-lite mix.