Effect of synthetic iron chelates on population densities of Fusarium oxysporum and the biological control agent Pseudomonas putida in soil

Although soil conducive to Fusarium wilt diseases was previously induced to become suppressive by addition of FeEDDHA (ferric ethylenediaminedi-o-hydroxyphenylacetic acid), addition of FeEDTA (ferric ethylenediaminetetraacetic acid) or FeEDDHA to soil infested with F. oxysporum f. sp. conglutinans (the radish wilt pathogen) did not significantly affect inoculum densities in rhizosphere soil in this study. Addition of 100 μg FeEDTA/g soil significantly decreased levels of Pseudomonas putida in rhizosphere soil; however, addition of 100–1000 μg FeEDDHA/g soil significantly increased population densities of P. putida in fallow and rhizosphere soils. The suggested mechanism was that Fe3+ available to the Fusarium was reduced by competition with EDDHA and that such competition in soil may give selective advantage to siderophore-producing antagonists such as P. putida.