Induced micronutrient toxicity in Petunia hybrida∗

This study was supported by Colorado Agricultural Experiment Station (Project 747) and Bedding Plants Foundation Inc.

Abstract

Plant micronutnent toxicity symptoms of petunia (Petunia hybrida) cv. Ultra Crimson Star were experimentally induced and characterized. Starting at the 3–4 true leaf stage, plants grown in peat‐lite mix in 11 cm pots were constantly fed for 5 weeks with fertilizer solutions containing 0.25, 0.5, 1, 2, 3, 4, 5, and 6 mM plus the control concentration of boron, copper, iron, manganese, molybdenum and zinc at pH 6.5. The control solution had 20 μM B, 0.5 μM Cu, 10 μM Fe, 10 μM Mn, 0.5 μM Mo, and 4 μM Zn. Foliar toxicity symptoms were produced when the nutrient solutions contained 0.5 mM (5.4 ppm) B, 0.5 mM (32 ppm) Cu, 0.5 mM (28 ppm) Mn, 0.25 mM (24 ppm) Mo, and 0.25 mM (16 ppm) Zn. Iron in the range of concentrations tested did not cause foliar toxicity. Reduction in dry matter yield was evident when 2 mM (22 ppm) B, 1 mM (64 ppm) Cu, 6 mM (335 ppm) Fe, 0.5 mM (28 ppm) Mn, 0.25 mM (24 ppm) Mo, and 0.5 mM (33 ppm) Zn were used in the fertilizer solution. Leaf chlorophyll contents decreased as Cu and Mn concentrations increased. Leaf chlorophyll contents increased as Fe in the fertilizer solution was elevated. The threshold tissue micronutrient levels that caused toxicity symptoms were also determined.

Notes

This study was supported by Colorado Agricultural Experiment Station (Project 747) and Bedding Plants Foundation Inc.

Associate Professor; Current address: Department of Horticulture and Forestry, North Dakota State University, Fargo, ND 58105

Visiting Professor: Dept. of Horticultural Breeding, Mokpo National University, Chonnam 534–729, South Korea

Graduate Student

Research Associate, Soils Laboratory. Address reprint requests to C.W. Lee.