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Appl Environ Microbiol. 1991 March; 57(3): 660-664
Copyright © 1991, American Society for Microbiology. All Rights Reserved.

Polygalacturonase Production by Agrobacterium tumefaciens Biovar 3

Raymond G. McGuire, Pablo Rodriguez-Palenzuela, Alan Collmer and Thomas J. Burr^*

¹ Department of Plant Pathology, Cornell University, Ithaca, New York 14853, and Department of Plant Pathology, New York State Agricultural Experiment Station, Geneva, New York 14456-0462²

ABSTRACT

Agrobacterium tumefaciens biovar 3 causes both crown gall and root decay of grape. Twenty-two Agrobacterium strains representing biovars 1, 2, and 3 were analyzed for tumorigenicity, presence of a Ti plasmid, ability to cause grape seedling root decay, and pectolytic activity. All of the biovar 3 strains, regardless of their tumorigenicity or presence of a Ti plasmid, caused root decay and were pectolytic, whereas none of the biovar 1 and 2 strains had these capacities. Isoelectrically focused gels that were activity stained with differentially buffered polygalacturonate-agarose overlays revealed that all of the biovar 3 strains produced a single polygalacturonase with a pH optimum of 4.5 and pIs ranging from 4.8 to 5.2. The enzyme was largely extracellular and was produced constitutively in basal medium supplemented with a variety of carbon sources including polygalacturonic acid. Lesions on grape seedling roots inoculated with A. tumefaciens biovar 3 strain CG49 yielded polygalacturonase activity with a pI similar to that of the enzyme produced by the bacterium in culture. These observations support the hypothesis that the polygalacturonase produced by A. tumefaciens biovar 3 has a role in grape root decay.

^* Corresponding author.

Present address: Subtropical Horticultural Research Station, U.S. Department of Agriculture, Miami, FL 33158.