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Physiology and Biochemistry

Bacterial Growth, Toxin Production, and Levels of Ornithine Carbamoyltransferase in Resistant and Susceptible Cultivars of Bean Inoculated with Pseudomonas phaseolicola. Samuel S. Gnanamanickam, Graduate Student, Department of Plant Pathology, University of Hawaii, Honolulu 96822; Suresh S. Patil, Professor, Department of Plant Pathology, University of Hawaii, Honolulu 96822. Phytopathology 66:290-294. Accepted for publication 3 September 1975. DOI: 10.1094/Phyto-66-290.

Time-course studies of growth and toxin production in culture were made with four isolates of Pseudomonas phaseolicola: G-50 and HB-36 (race 2) and HB-46 and HB-20 (race 1). In culture, all isolates increased approximately to the same population level (10⁸-10⁹ cells/ml) and all isolates except HB-20 produced toxin. Time-course experiments to measure growth, toxin production, and changes in the level of the enzyme, ornithine carbamoyltransferase (OCT), in bean leaf tissue, were made by inoculating two resistant and two susceptible bean cultivars with isolates HB-36 and HB-20 of the pathogen in separate experiments. In leaves of the susceptible bean cultivars “Resistant” Cherokee Wax and Red Kidney, both isolates increased to 10⁹ cells per 1.2 cm² of leaf area from an initial level of 10³ cells, but only HB-36 produced toxin. Also, in leaves of susceptible cultivars “Resistant” Cherokee Wax and Red Kidney, inoculated with HB-36, OCT activity averaged 53% and 71%, respectively, of that found in noninoculated leaves. In the resistant cultivars P.I. 150514 and GN #27, both isolates had much slower rates of multiplication than in susceptible cultivars; the highest number of bacterial cells observed was 10⁵ cells per 1.2 cm² leaf area. In spite of this substantial increase in number of cells, no toxin was detected in resistant leaf tissues, including those that were inoculated with the toxin-producing isolate (HB-36) and there was no significant inhibition of OCT until 3 days after inoculation. Inhibition coincided with the appearance of the tissue browning and cell collapse characteristic of a hypersensitive reaction.