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Influence of Trace Amounts of Cations and Siderophore-Producing Pseudomonads on Chlamydospore Germination of Fusarium oxysporum. Yigal Elad, Visiting scientist, Plant Pathology and Weed Science, Colorado State University, Fort Collins 80523, Department of Plant Pathology and Microbiology, Faculty of Agriculture, The Hebrew University of Jerusalem, Rehovot 76100, Israel; Ralph Baker, professor, Plant Pathology and Weed Science, Colorado State University, Fort Collins 80523. Phytopathology 75:1047-1052. Accepted for publication 10 April 1985. Copyright 1985 The American Phytopathological Society. DOI: 10.1094/Phyto-75-1047.

A siderophore(s) from several Pseudomonas spp. and P. putida was concentrated by dialysis and freeze-drying. The concentrated siderophore was active after 3 mo of storage. The cations Mg2+, Mn2+, Ca2+, Co2+, Cu2+, Zn2+, Al3+, K1+, Na1+, NH41+, or Ni1+ competed with Fe3+ on binding sites of the siderophore in vitro; however, affinity of the siderophore to Fe3+ was higher than to the other cations. Added cations delayed multiplication of Pseudomonas spp. in soil. The concentrated siderophore inhibited germination of chlamydospores of Fusarium oxysporum f. sp. cucumerinum up to 70.2%. This effect was nullified by an excess of iron in soil. The chelating agent EDDHA (ethylenediaminedi-O-hydroxyphenylacetic acid) had similar effects on chlamydospore germination in raw soil as did the siderophore, whereas FeEDDHA was ineffective in raw soil. Both chelators effectively inhibited chlamydospores of F.o. f. sp. cucumerinum in the rhizospheres of cucumber (Cucumis sativus) but did not inhibit germination of F. solani f. sp. phaseoli in rhizospheres of beans (Phaseolus vulgaris).