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Joseph P. Albano, William B. Miller, and Mary C. Halbrooks

A specific physiological disorder, bronze speckle (J.P.A.'s nomenclature), was consistently induced in `First Lady' and `Voyager' marigold with Fe-DTPA concentrations greater than 0.018 mm Fe-DTPA (1 ppm) applied to a soilless medium. The disorder was characterized by specific symptomology distinguished visually by speckled patterns of chlorosis and necrosis, and downward curling and cupping of leaves. The percentage of total leaf dry weight affected with symptoms generally increased with increasing Fe-DTPA treatments. Symptomatic leaf tissue had a greater Fe concentration than corresponding asymptomatic leaf tissue. Leaf Mn concentrations in symptomatic and asymptomatic tissue were similar. In `First Lady', older leaf tissue accumulated more total Fe and was associated with more severe symptoms than younger tissue. Media leachate Fe concentrations increased over 6 weeks and were larger at greater Fe-DTPA treatments. Adjustment of nutrient solution pH to 4.0, 5.25, or 6.5 did not alter media pH, nor did it prevent disorder symptoms. Application of Fe-DTPA containing nutrient solution to a soilless medium resulted in leachate Fe levels 3 times greater than for FeSO4 treatments. Chemical names used: ferric diethylenetriaminepentaacetic acid, monosodium salt (Fe-DTPA).

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Joseph P. Albano and William B. Miller

The susceptibility of seven African marigold (Tagetes erecta L.) cultivars to iron toxicity was assessed. Plants were grown in a greenhouse in a soilless medium and Fe-DTPA was incorporated into the nutrient solution at either 0.018 mmol·L-1 (low) or 0.36 mmol·L-1 (high). Symptoms of Fe toxicity (bronze speckle disorder in marigold characterized by chlorotic and necrotic speckling and downward leaf cupping and curling) developed only in the high-Fe treatment. The concentration of Fe in leaves in the high-Fe treatment was 5.6 and 1.7 times as great as in the low-Fe treatment for `Orange Jubilee' and `Discovery Orange', respectively. Based upon the percentage of plants affected and leaf symptom severity, relative cultivar susceptibility to Fe toxicity was Orange Jubilee > First Lady > Orange Lady > Yellow Galore > Gold Lady > Marvel Gold > Discovery Orange. Chemical names used: ferric diethylenetriaminepentaacetic acid, disodium salt dihydrate (Fe-DTPA).

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Joseph P. Albano and William B. Miller

Excised roots of `First Lady' marigold (Tagetes erecta L.) grown in an aerated 0 Fe nutrient solution had Fe(III)-DTPA reductase activity 14-fold greater, and an enhanced ability to acidify the rhizosphere than plants grown in a solution containing 0.018 mm (1 ppm) Fe-DTPA. Reductase activity and rhizosphere acidification of plants grown in 0.018 and 0.09 mm Fe-DTPA were similar. Manganese concentration in leaves of plants grown in the 0 Fe treatment was 2-fold greater than in leaves of plants grown in the 0.018 mm Fe-DTPA treatment. These results indicated that `First Lady' marigold is an Fe-efficient plant that possesses both an inducible or adaptive reductase system and the ability to acidify the rhizosphere, and that these Fe-efficiency reactions do not occur when Fe is sufficient. Chemical name used: ferric diethylenetriaminepentaacetic acid, monosodium salt (Fe-DTPA).

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Nancy K. Todd

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.

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Joseph P. Albano and Donald J. Merhaut

, FeEDTA, FeDTPA, FeEDDHA, and FeSO 4 ) had no influence on marigold leaf count, plant height, leaf dry mass, or leaf greenness nor were there any signs of Bronze Speckle or Micronutrient Toxicity Syndrome (MTS) [Fe, Mn, or a combination of both toxicity

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Ritu Dhir, Richard L. Harkess, and Guihong Bi

inhibited as a result of elevated air temperatures or bleaching. Literature Cited Albano, J.P. Miller, W.B. Halbrooks, M.C. 1996 Iron toxicity stress causes bronze speckle, a specific physiological disorder of marigold ( Tagetes erecta L.) J. Amer. Soc

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Ryan W. Dickson, Paul R. Fisher, and William R. Argo

physiology of iron acquisition in marigold ( Tagetes erecta L.) J. Amer. Soc. Hort. Sci. 121 438 441 Albano, J.P. Miller, W.B. Halbrooks, M.C. 1996 Iron toxicity stress causes bronze speckle, a specific physiological disorder of marigold ( Tagetes erecta L