947 SCREENING MARIGOLD CULTIVARS FOR SUSCEPTIBILITY TO IRON TOXICITY
Marigolds are susceptible to a specific nutritional disorder known as “bronze speckling”. It has been reported that the disorder is caused by excessive uptake of iron by the plant, which may be due to high levels of Fe in the soil solution or low soil pH. In this experiment, 12 cultivars of marigold (Tagetes erecta and T. patula) were grown using increasing levels of Fe (0, 5, 15, and 20 mg/l) from Fe DTPA. In the susceptible cultivars, symptoms were observed within 5 days of initial treatment and appeared as a chlorotic mottling. Initial symptoms resembled spider mite damage on older leaves, which gradually became bronze colored in appearance, and finally became necrotic. Downward cupping of leaves was observed in severely affected plants. Severity of necrosis and percent of plant leaves affected (dry weight basis) were evaluated to determine susceptibility of the different cultivars to the disorder. There was a direct correlation between increasing concentration of Fe and occurrence and severity of symptoms. The most susceptible to least susceptible cultivars were determined to be: First Lady, Inca, Discovery, Galore, Pineapple Crush, Perfection Excel, Voyager All Seasons, Nugget, Zenith, Voyager F1 and Diamond Jubilee.