IRON CHELATE INDUCIBLE IRON/MANGANESE TOXICITY IN ZONAL GERANIUM

Leaf symptoms of a physiological disorder of cutting geranium (Pelargonium x hortorum L.H. Bailey 'Aurora') were induced with FeDTPA treatments ranging from 0.02 mM (1 ppm) to 1.12 mM (60 ppm) applied to a soilless peat-based medium. Symptoms included marginal/nterveinal chlorosis that progressed to marginal/interveinal necrosis and in extreme cases whole leaf necrosis. Iron (Fe) concentration increased with increasing FeDTPA level in both symptom and asymptom tissues. Within the same FeDTPA treatments symptom tissue had higher concentration of Fe and manganese (Mn) than asymptom tissue. Manganese in symptom tissue decreased as FeDTPA level increased; whereas Mn concentration of asymptom tissue were similar among all FeDTPA treatments. Preplant addition of dolomite to maintain medium pH within the range of 5.8-6.2 lowered Fe and Mn concentration in both symptom and asymptom tissue and medium leachates; however, liquid dolomite drenches during the crop cycle had little effect on tissue Fe and Mn. This disorder results from increased levels of Fe and Mn in the plant tissue and should be referred to as Fe/Mn toxicity.