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Physiology and Biochemistry

Relation of Tobacco Hypersensitivity to Pathogenicity of Erwinia rubrifaciens. H. R. Azad, Department of Plant Pathology, University of California, Davis 95616; C. I. Kado, Department of Plant Pathology, University of California, Davis 95616. Phytopathology 74:61-64. Accepted for publication 7 July 1983. Copyright 1984 The American Phytopathological Society. DOI: 10.1094/Phyto-74-61.

Thirty-five strains of Erwinia rubrifaciens derived from 16 counties in California induced the hypersensitive response (HR) in Havana tobacco leaves at high inoculum levels (3 109 cfu/ml) and were pathogenic in Hartley walnut trees. However, HR- mutants obtained by either transposon Tn10 insertion or nitrosoguanidine mutagenesis were equally pathogenic, indicating a lack of correlation between HR and pathogenicity. Endopolygalacturonic acid trans-eliminase (PATE) activity was present in osmotic shock extracts of both the wild-type strain and the mutant derivatives. These findings do not permit the use of the tobacco hypersensitivity reaction for a rapid means of screening for pathogenic strains of E. rubrifaciens. They also suggest that more than PATE is involved in the HR in tobacco.

Additional keywords: Juglans regia, plasmid pSa.