MICRONUTRIENT TOXICITY IN FRENCH MARIGOLD

The influence of elevated levels of micronutrients on the growth and f lowering of French marigold (Tagetes patula L.) was investigated. Plan ts were grown with nutrient solution containing 0.25, 0.5, 1, 2, 3, 4, 5, or 6 mM boron (B), copper (Cu), iron (Fe), manganese (Mn), molybde num (Mo), or zinc (Zn) and toxicity development was monitored. The thr eshold micronutrient concentrations that induced visible foliar toxici tysymptoms were 0.5 mM B, 4 mM Cu, 4 mM Fe, 2 mM Mn, 1 mM Mo, and 5 mM Zn. The dry matter yields during the 5 week experimental period were reduced when micronutrient concentrations exceeded 0.5 mM B, 3 mM Cu, 3 mM Fe, 6 mM Mn, 0.5 mM Mo, and 5 mM Zn in the fertilizer solution. L eaf chlorophyll contents decreased when the nutrient solution concentr ations of Cu, Fe, and Mn were greater than 0.5 mM, 3 mM, and 2 mM, res pectively. Visual toxicity symptoms of the six micronutrients were cha racterized.