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Manganese toxicity in marigold as affected by calcium and magnesium
Iron/manganese toxicity disorder in marigold (Tagetes erecta L.) has been related to high concentrations of Mn and low concentrations of Ca and Mg in the affected leaves. Preplant addition of micronutrients in the media combined with constant feed program and low medium pH create favorable conditions for the development of Mn toxicity in greenhouse crops. Deficiency of Ca or Mg is due in part to low medium pH and to a lack of Mg and Ca in many of the fertilizers used in greenhouse production. The objectives of this research were to determine the relationship of Mn toxicity to the incidence of Fe/Mn toxicity disorder in marigold, and to evaluate the effect of low Mg supply and/or low Ca supply on the occurrence of the toxicity. Six experiments were conducted. Plants of Tagetes erecta L. ‘First Lady’ were started from seeds and then grown in solution culture supplying different concentrations of Mn, Ca and Mg depending on the objectives of each experiment. Symptoms were described for each experiment. When the plants were harvested, their dry weights were taken and their tissues were analyzed for Mn, Fe, Ca, and Mg concentrations. The symptoms of Mg deficiency included stunting, chlorotic and necrotic areas on the leaves. The symptoms of Ca deficiency included chlorosis and curling, especially of the new leaves. The symptoms of Mn toxicity included curled leaves, bleached patches and brown spots on the leaves. These symptoms of Mn toxicity are similar to those related to Fe/Mn toxicity disorder. The incipient deficiency solution concentration of Mg was 10 mg/l (internal incipient deficiency concentration was 1.5%). The incipient deficiency solution concentration of Ca was 20 mg/l (internal incipient deficiency concentration was 0.54%). The critical toxicity concentration of Mn was 4.5 mg/l (internal critical toxicity concentration was 270 mg/kg DW). Low Ca in solution (20 mg/liter) increased the sensitivity of marigold to high levels of Mn in solution by reducing the critical toxicity concentration of Mn from 4.5 to 0.5 mg/liter. Similar results were found when both Ca and Mg were low. Iron/manganese toxicity disorder can be attributed to Mn toxicity. Low Ca supply or low Ca and Mg supplies are factors favoring the occurrence of the disorder. Low Mg supply, alone does not seem to affect Mn toxicity in marigold. Based on this research, high Ca supply could alleviate the harmful effects of Mn toxicity in marigold. Low Mn supply could prevent the toxicity problems. Agricultural practices and nutritional regimes that reduce the availability of Mn and increase the availability of Ca could reduce the occurrence of Fe/Mn toxicity disorder in marigold and similar physiological disorders in other bedding plants grown in soilless media. Monitoring Mn supply and fertilizing with Ca could prevent or reduce Mn toxicity to floriculture plants.
Eaton, Touria El-Jaoual, "Manganese toxicity in marigold as affected by calcium and magnesium" (2002). Doctoral Dissertations Available from Proquest. AAI3056221.