Relation of Tobacco Hypersensitivity to Pathogenicity ofErwinia rubrifaciens

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Abstract
A total of 35 strains of E. rubrifaciens derived from 16 counties in California [USA] induced the hypersensitive response (HR) in ''Havana'' tobacco [Nicotiana tabacum] leaves at high inoculum levels (3 .times. 109 cfu/ml) and were pathogenic in ''Hartley'' walnut [Juglans regia] 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.