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Tumor Initiation Complementation on Bean Leaves by Mixtures of Tumorigenic and Nontumorigenic Agrobacterium rhizogenes. James A. Lippincott, Professor, Department of Biological Sciences, Northwestern University, Evanston, IL 60201; Barbara B. Lippincott, Senior Research Associate, Department of Biological Sciences, Northwestern University, Evanston, IL 60201. Phytopathology 68:365-370. Accepted for publication 12 September 1977. Copyright 1978 The American Phytopathological Society, 3340 Pilot Knob Road, St. Paul, MN 55121. All rights reserved.. DOI: 10.1094/Phyto-68-365.

The enhancement (as much as 50-fold) of tumor initiation (complementation) on bean leaves shown by certain mixtures of nontumorigenic and tumorigenic agrobacteria was investigated with tumorigenic strain ATCC 15834 and nontumorigenic strain TR7 of Agrobacterium rhizogenes. When either strain was inoculated with wounding at different times after the other, maximum tumor initiation was observed when the second strain was added 3 hr after the first. A 6-hr interval between inoculation of the two bacteria resulted in 40 to 60% as many tumors as obtained with a 3-hr interval but no enhancement occurred when the two strains were inoculated 24 hr apart. The optimum ratio of TR7 to ATCC 15834 for tumor initiation varied with the concentration of bacteria in the inoculum; the higher the concentration, the greater the proportion of TR7 necessary for maximum tumor initiation. The contribution of each strain to this effect when inoculated second was reduced by heat inactivated bacteria, suggesting that both strains undergo site attachment in order to participate in the complmentation process. New tumors were detected up to day 8 or 9 on leaves inoculated with two bacteria. This was similar to results obtained with virulent prototrophic strains of Agrobacterium, although both TR7 and ATCC 15834 are auxotrophs and the tumors initiated by ATCC 15834 alone, like those by other auxotrophs, are detected within 5 days after inoculation. A model consistent with these data, where both bacteria undergo site attachment independently at different wound sites, allowing transfer between sites of a product which is limiting for tumor initiation at one site, is suggested to account for these effects.