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Physiology and Biochemistry

Pathogenicity of Strains of Pseudomonas syringae pv. savastanoi and Their Indoleacetic Acid-Deficient Mutants on Olive and Oleander. G. Surico, Department of Plant Pathology, University of California, Davis 95616, Present address: Istituto del C.N.R. su le Tossine e Micotossine dei Parassiti Vegetali, Istituto di Patologia Vegetale, Universita degli Studi, Facolta di Agraria, 70126 Bari, Italy; L. Comai(2), and T. Kosuge(3). (2)(3)Department of Plant Pathology, University of California, Davis 95616, (2)Present address: Calgene Inc., 1910 Fifth Street, Suite F, Davis, CA 95616. Phytopathology 74:490-493. Accepted for publication 19 October 1983. Copyright 1984 The American Phytopathological Society. DOI: 10.1094/Phyto-74-490.

Previous investigations have shown that indoleacetic acid (IAA) production by strains of Pseudomonas syringae pv. savastanoi (pv. savastanoi) from oleander is necessary for formation of galls on oleander. The present study compared the pathogenicity on olive and oleander plants of wild-type and indoleacetic acid (IAA)-deficient (Iaa- ) mutant strains of pv. savastanoi from olive, oleander, and privet. All wild-type strains from olive, oleander, and privet induced galls on olive. Only wild-type isolates from oleander were tumorigenic on oleander. An exception was observed with isolate EW1017 from olive which also caused galls on oleander; however, this strain resembled strains from oleander in that IAA genes were plasmidborne. Iaa- mutants of the strains from olive and privet did not induce galls on olive and oleander. Iaa- mutants of strains from oleander produced no symptoms on oleander plants, but induced atypical galls on olive plants. The role of bacterial production of IAA in gall formation on the olive and oleander knot diseases was thus confirmed.

Additional keywords: olive knot, phytohormones, plasmids.