A semiquantitative bioassay for relative virulence of Agrobacterium tumefaciens strains on Bryophyllum daigremontiana

Abstract

An assay to determine the relative virulence of wild-type and mutant strains of Agrobacterium tumefaciens on leaves of Bryophyllum daigremontiana has been developed. This assay is reproducible, is easy to learn, is not time consuming, and requires little space. The relative virulence of cellulose-minus mutants of A. tumefaciens was investigated with this assay. Some of these mutants were unaltered in virulence, while others showed a marked reduction in virulence. The wound sites were scored as positive or negative for tumor formation once a week for 6 weeks. Tumors began to form on the plants after 1 or 2 weeks; new tumors ceased to form after 4 to 6 weeks.We found that the best way to quantitate bacterial virulence in this assay was to determine the number of bacteria needed to form tumors at 50% of the inoculated sites. Other parameters, such as tumor weight, diameter, and length of time to form tumors, were explored but were not found to give a linear response as the number of bacteria inoculated increased. Figure 1 shows the effect of changes in the number of

Structural and putative regulatory genes involved in cellulose synthesis in Rhizobium leguminosarum bv. trifolii

“…In Ag. tumefaciens, the cellulose fibrils serve to bind the bacteria tightly to the plant host cells and mutants which cannot synthesize cellulose are reduced in virulence, but still capable of infection, at least under laboratory conditions (Matthysse et al, 1981 ;Minnemeyer et al, 1991). Similarly, Smit et al (1987) showed that fibril-negative as well as fibril-overproducing mutants of R. leguminosarum showed a normal nodulation behaviour, which was confirmed for R. leguminosarum bv.…”

Isolation and Characterization of Agrobacterium Strains from Soil: A Laboratory Capstone Experience

“…In this approach, either Kalanchoe —a nursery/house plant (8)—or carrot slices (6) are inoculated with student isolates. Use of a pathogenic strain in the infectivity assay will result in lesions, roots, or galls appearing on plant tissue in four weeks.…”

Attachment of Rhizobiaceae to Plant Cells

“…Cel mutants also bind loosely to wound sites on leaves of Bryophyllum daigremontiana and can be removed by gentle water washing (Matthysse, 1983). These mutants are virulent, but are much reduced in virulence (10 to WOO-fold depending on the particular mutation) when compared to the wild type parent (Minnemeyer et al, 1991). Little is known about the genes required for the attachment of other biotypes of agrobacteria to host cells.…”