Manganese Toxicity in Marigold as Affected by Calcium

Iron-manganese disorder in marigold has been related to high concentrations of Mn and low concentrations of Ca 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 is due principally to low Ca in some fertilizers used in greenhouse production.  To investigate the effects of Ca on Mn toxicity (growth, appearance, and nutrient concentrations) in marigold (Tagetes erecta L. ‘First Lady’), a factorial, solution-culture study with various Ca (20 to 100 mg/L) and Mn (0.5 to 6.5 mg/L) concentrations was conducted. Treatments 20/6.5, 20/4.5, 20/2.5, and 100/6.5 mg/L Ca/Mn concentrations resulted in stunted plants with small brown spots, interveinal chlorotic patches and necrotic symptoms on the tips and margins of the leaves, and deformed leaves. Treatments 20/0.5, 100/2.5, and 100/4.5 resulted in stunted plants relatively free of symptoms. The treatment 100/0.5 resulted in fully grown and healthy looking plants.  Concentrations of Ca at 20 mg/L (incipient deficiency concentration of Ca in marigold) reduced the critical toxicity concentration of Mn from 4.5 to 2.5 mg/L nutrient solution. The interaction between Ca and Mn in the solution had a highly significant effect on Fe and Mn in the plant tissue.  Low Ca and high Mn in the medium resulted in increased concentration of Fe in the roots and Mn in the leaves and stems.  At 20mg/L Ca in the nutrient solution and high Mn, the roots Fe was 1300 mg/kg dry weight (DW) whereas the Mn concentration in the roots, new leaves and old leaves were 500, 1300 and 1600 mg/Kg DW respectively.  These results suggest that low Ca and high Mn nutrition lead to the Fe-Mn disorder in marigold.