Comparative study ofAgrobacteriumbiotypes 1, 2 and 3 by electrophoresis and serological methods

Cocolonization of the rhizosphere by pathogenic agrobacterium strains and nonpathogenic strains K84 and K1026, used for crown gall biocontrol

The crown gall biocontrol agent strain K84 and three mutants derived from it, K1026 (Tra- deletion mutant of pAgK84), K84 Agr- (lacking pAgK84), and K1143 (lacking pAgK84 and pNoc), significantly reduced gall formation caused by two pathogenic strains resistant to agrocin 84 in peach x almond seedlings planted in infested soil. Cocolonization of roots by pathogenic and nonpathogenic strains was observed in these biocontrol experiments under field conditions. In spite of the efficient biocontrol observed, average populations consisting of 10(2) and 10(6) pathogenic agrobacteria per g of root were found 8 months after planting. The total numbers of pathogenic bacteria on roots were similar for plants treated with the biocontrol strains and for the untreated plants. Strain K84 and the genetically engineered organism K1026 survived at a level of 10(6) agrocin 84-producing bacteria per g of root. The population size of genetically engineered strain K1026 was not significantly different than the population size of wild-type strain K84 8 months after root inoculation. Strains K84 and K1026 controlled two pathogens resistant to agrocin 84 without reducing the total number of pathogenic bacteria in the root system. In addition, this study shows that some biological control activity of strain K84 against agrocin 84-resistant pathogens is independent of plasmids pAgK84 and pNoc.

A simple and efficient PCR method for the detection of Agrobacterium tumefaciens in plant tumours

A simple PCR protocol was developed for identifying Agrobacterium as the causal agent of the tumours produced by this bacterium in plant material. The sensitivity of this method was compared with that of bacterial isolation using common and selective media with a previous enrichment step. More than 200 samples from tumours of naturally infected and inoculated plants from several hosts including almond, peach x almond hybrids, apricot, rose, tobacco, tomato, raspberry, grapevine and chrysanthemum, were analysed by both methods. PCR was the most efficient method for detecting the bacterial aetiology of the plant tumours. Agrobacterium tumefaciens was better detected in crown and root tumours than in aerial tumours with all the methods assayed in inoculated plants. A comparison between the efficiency of the diagnosis by analysing pieces from the external and internal part of the tumour showed no differences between them.

Identification of Agrobacterium strains by PCR-RFLP analysis of pTi and chromosomal regions

Chromosomes and Ti plasmids of 41 Agrobacterium strains, belonging to biovars 1, 2, 3, and Agrobacterium rubi species were characterized by the restriction fragment length polymorphism of PCR-amplified DNAs. Profiles that were obtained by the analysis of the amplified 16S rDNA confirmed the grouping of the strains according to their species. Higher polymorphism was detected in the intergenic spacer between the 16S rDNA and 23S rDNA genes, allowing efficient discrimination of strains. Identification of most strains was possible, and the genetic relatednesses of Agrobacterium strains could be estimated. The analysis of the plasmid Ti encoded regions between the tmr and nos genes, and the virA and virB2 genes, allowed fingerprinting of Ti plasmids. Genomic typing by the rapid PCR-RFLP method is thus shown to be useful for an independent identification of strains and of the conjugative Ti plasmids.

Plasmid Heterogeneity in Spanish Isolates of Agrobacterium tumefaciens from Thirteen Different Hosts

Plasmid DNA was isolated from 80 Spanish isolates of Agrobacterium tumefaciens from 13 hosts of several geographical and temporal origins. One to five plasmids occurred in all of the isolates studied. Plasmid sizes varied between 5 and greater than 1,000 MDa. Generally, there was no correlation between plasmid number or size and geographical origin, host, biovar, sensitivity to agrocin 84, or opine-catabolizing ability of the different isolates.