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Fungistatic Activity of Water-Soluble Fluorescent Pigments of Fluorescent Pseudomonads. I. J. Misaghi, Department of Plant Pathology, University of Arizona, Tucson 85721; L. J. Stowell(2), R. G. Grogan(3), and L. C. Spearman(4). (2)(4) Department of Plant Pathology, University of Arizona, Tucson 85721; (3)Department of Plant Pathology, University of California, Davis 95616. Phytopathology 72:33-36. Accepted for publication 13 April 1981. Copyright 1982 The American Phytopathological Society. DOI: 10.1094/Phyto-72-33.

Water-soluble fluorescent pigments of 156 fluorescent Pseudomonas isolates of plant pathogenic and saprophytic species inhibited the growth of Geotrichum candidum. Other fungal species that showed sensitivity to the pigments produced by four Pseudomonas isolates were Rhizoctonia solani, Sclerotinia sclerotiorum, Phymatotrichum omnivorum, Phytophthora megasperma, and Pythium aphanidermatum. A direct correlation was established between the quantity of a partially purified pigment obtained from an isolate of Pseudomonas fluorescens and its fungistatic activity against P. aphanidermatum. The inhibition could be counteracted by adding iron to the medium in excess of chelating capacity of the added pigment. Results show that fungistatic activity of the pigment is due to its ability to remove iron from the medium by forming an iron-pigment complex. The pigment exhibited properties similar to those of known microbial iron-chelating substances (siderophores).