Calcium Deficiency in Marigold

Iron-manganese toxicity disorder in marigold has been related to high concentrations of Fe and Mn and low concentrations of Ca and Mg in the affected leaves.  This disorder may occur because of high Fe and Mn availability in media and lack of Ca in many fertilizers used in greenhouse crop production. To investigate the effect of Ca nutrition on marigold (Tagetes erecta L. ‘First Lady’) growth, appearance, and nutrient (Mn, Fe, Ca, and Mg) accumulation in the plant tissue, a solution-culture study with various Ca concentrations (2.5 to 100 mg/L) was conducted.  After 90 days of growth, concentrations of Ca up to 15 mg/L resulted in stunted plants with chlorotic and necrotic symptoms on the leaves.  The concentration 20 mg Ca/L resulted in stunted plants free of symptoms.  Concentrations above 20 mg/l resulted in healthy plants with no leaf symptoms or stunting.  The concentration 20 mg/L Ca may thus be considered as the incipient deficiency concentration for marigold.  At this solution concentration, the Ca in the plant shoots was 0.54% dry weight, which is a low concentration relative to well-nourished marigold.  Relative to adequate Ca nutrition, a low supply of Ca had no effect on Fe concentration in the growing point (buds and newest leaves) but resulted in a high concentration of Fe in the old leaves and old stems.  Calcium deficiency did not affect the concentration of Mn in the old parts of the shoots but resulted in high concentrations of Mn in the growing points.  Low Ca in the solution resulted in low Ca and high Mg in the shoots.  This research suggests that inadequate Ca nutrition lead to increased Mn in marigold making it susceptible to Fe-Mn toxicity disorder.