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Lack of Correlation of In Vitro Antibiosis with Antagonism of Ice Nucleation Active Bacteria on Leaf Surfaces by Non-Ice Nucleation Active Bacteria. S. E. Lindow, Associate professor, Department of Plant Pathology, University of California, Berkeley 94720; Phytopathology 78:444-450. Accepted for publication 13 October 1987. Copyright 1988 The American Phytopathological Society. DOI: 10.1094/Phyto-78-444.

Only 58% of 88 bacterial strains antagonistic to ice nucleation active strains of Pseudomonas syringae and Erwinia herbicola on leaf surfaces produced compounds inhibitory to P. syringae on any of several culture media tested. Eighty-two percent of those antagonistic to P. syringae in vitro produced iron-regulated antibiotics, 6% produced trypsin-sensitive antibiotics, and 39% produced trypsin or iron-insensitive antibiotics that were inhibitory to P. syringae. Thirty-one percent of the bacterial strains antagonistic to P. syringae on rich culture media were not inhibitory when grown on a defined medium similar in composition to leaf leachates. Frost injury to corn plants treated with mutant strains deficient in production of one or more inhibitory compounds and derived from 24 of 25 parental antibiotic-producing strains did not differ significantly from corn treated with parental strains. Leaf surface populations of antibiotic-deficient mutants generally did not differ significantly from their parental strain, whether applied 2 days before or immediately after challenge inoculations of P. syringae. P. syringae populations and the numbers of bacterial ice nuclei were significantly lower on plants treated with antibiotic-deficient mutants or their parental strains either two days before or immediately after challenge inoculations with P. syringae. Antibiotic production by epiphytic bacteria on several laboratory media is not correlated with biological control of ice nucleation active bacteria on plants.

Additional keywords: siderophore, Zea mays, phylloplane.