Last summer, a marigold flower sample was submitted to the NCSU Plant Disease and Insect Clinic to determine the cause of the blossom discoloration. No data existed for comparison to evaluate the nutrient concentration in the flowers to help with the diagnosis. While preparing for a marigold seminar at Cultivate25, the team decided to induce Ca deficiency and sample deficient and complete blooms of African marigold (Tagetes erecta) to determine actual concentrations.
Calcium evaluation
Whole blooms were sampled from plants subjected to Ca-deficient conditions, which had developed extensive symptoms, and flowers from healthy plants grown with a complete Hoagland's fertilizer solution. When comparing Ca concentrations in symptomatic flowers and healthy ones, levels were lower in deficient plants (0.09% Ca) compared with 0.39% Ca in the asymptomatic plants. Lower values in deficient plants were expected, yet it was surprising to see how low Ca is in healthy blooms.
Researchers also sampled the most recently matured leaves (MRLM) from both healthy and Ca-deficient plants for comparison. Calcium concentrations were 10x higher in healthy leaves (2.36% Ca) compared with 0.20% Ca in the deficient plants. As a comparison, Bryson and Mills in the Plant Analysis Handbook 3 report African marigold (Tagetes erecta) leaf tissue values from survey plants at 0.88 to 2.74% Ca.
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