Jp. Albano et al., IRON TOXICITY STRESS CAUSES BRONZE SPECKLE, A SPECIFIC PHYSIOLOGICAL DISORDER OF MARIGOLD (TAGETES-ERECTA L), Journal of the American Society for Horticultural Science, 121(3), 1996, pp. 430-437
A specific physiological disorder, bronze speckle (J.P.A.'s nomenclatu
re), was consistently induced in 'First Lady' and 'Voyager' marigold w
ith Fe-DTPA concentrations greater than 0.018 mM Fe-DTPA (1 ppm) appli
ed to a soilless medium. The disorder was characterized by specific sy
mptomology distinguished visually by speckled patterns of chlorosis an
d necrosis, and downward curling and cupping of leaves. The percentage
of total leaf dry weight affected with symptoms generally increased w
ith increasing Fe-DTPA treatments, Symptomatic leaf tissue had a great
er Fe concentration than corresponding asymptomatic leaf tissue. Leaf
Ran 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 leach
ate Fe concentrations increased over 6 weeks and were larger at greate
r 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 medi
um resulted in leachate Fe levels 3 times greater than for FeSO4 treat
ments. Chemical names used: ferric diethylenetriaminepentaacetic acid,
monosodium salt (Fe-DTPA).