Induction of a Hypersensitivelike Reaction in Four-o’clock by Clavibacter michiganensis subsp. michiganensis. R. D. Gitaitis, Department of Plant Pathology, University of Georgia, Coastal Plain Experiment Station, Tifton 31793. . Plant Dis. 74:58-60. Accepted for publication 1 August 1989. Copyright 1990 The American Phytopathological Society. DOI: 10.1094/PD-74-0058.

Clavibacter michiganensis subsp. michiganensis produced an apparent hypersensitive reaction (HR) in four-o’clock (Mirabilis jalapa) when suspensions containing 10⁸ cfu of bacteria per milliliter of diluent were infiltrated into the intercellular spaces of leaf panels. A typical HR occurred in response to 34 virulent C. m. subsp. michiganensis strains and was independent of temperature within the range tested (18–43 C). Injection of four-o’clock with bacterial suspensions was an accurate and rapid way to distinguish C. m. subsp. michiganensis from other bacteria with similar colony morphology recovered from standard or semiselective bacteriological media. Strains of Erwinia herbicola, Pseudomonas fluorescens, and coryne-formlike bacteria that failed to elicit HR in four-o’clock were nonpathogenic to tomato (Lycopersicon esculentum), whereas all strains eliciting HR caused typical symptoms of bacterial canker on tomato and had the characteristics of C. m. subsp. michiganensis.