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A Genomic Region from Pseudomonas fluorescens Pf-5 Required for Pyrrolnitrin Production and Inhibition of Pyrenophora tritici-repentis in Wheat Straw. William F. Pfender, Department of Plant Pathology, Kansas State University, Manhattan 66506; Jennifer Kraus(2), and Joyce E. Loper(3). (2)(3)USDA, ARS, Horticultural Crops Research Laboratory, 3420 NW Orchard Ave., and Department of Botany and Plant Pathology, Oregon State University, Corvallis 97330. Phytopathology 83:1223-1228. Accepted for publication 11 June 1993. Copyright 1993 The American Phytopathological Society. DOI: 10.1094/Phyto-83-1223.

Pseudomonas fluorescens strain Pf-5, which produces many antifungal metabolites including pyrrolnitrin, inhibited mycelial growth of Pyrenophora tritici-repentis in agar culture and suppressed ascocarp formation by the fungus on axenically infested wheat straw kept moist during incubation. Purified pyrrolnitrin was similarly inhibitory. A Tn5 mutant of Pf-5 that did not produce detectable levels of pyrrolnitrin did not inhibit P. tritici-repentis on a culture medium or on wheat straw. A genomic region of Pf-5 was cloned that restored the pyrrolnitrin-deficient Tn5 mutant to pyrrolnitrin production and antagonism to P. tritici-repentis in culture. Pf-5 did not persist or suppress P. tritici-repentis on naturally infested wheat straw incubated under simulated field conditions of fluctuating moist and dry periods.