SEASONAL FLUCTUATION OF AGROBACTERIUM TUMEFACIENS POPULATIONS IN WALNUT ORCHARD SOIL

Authors: Kluepfel, Daniel; SUDARSHANA, PADMA - UC DAVIS,PLANT PATHOLOGY

Submitted to: American Phytopathological Society Annual Meeting
Publication Type: Abstract Only
Publication Acceptance Date: 7/1/2006
Publication Date: 8/1/2006
Citation: Kluepfel, D.A., Sudarshana, P. 2006. Seasonal fluctuation of agrobacterium tumefaciens populations in walnut orchard soil. American Phytopathological Society Annual Meeting.

Interpretive Summary:

Technical Abstract: Crown gall disease caused by the bacterium Agrobacterium tumefaciens causes significant economic loss in commercial walnut orchards and nursery operations in California. To aid in development of disease control strategies, it is important to understand the structure and dynamics of A. tumefaciens populations in soil. Here we report on the seasonal variation of pathogenic and non-pathogenic A. tumefaciens strains in soil around both diseased and healthy trees using culture based and culture-independent methods. Soil samples were collected monthly and A. tumefaciens was enumerated on 1A containing tellurite with populations ranging from 10⁴ to 10⁶ CFU/g over the sample period. Using Ti-plasmid and chromosomal-specific primers, randomly selected colonies on 1A-tellurite were subjected to PCR based screening to identify virulent and avirulent strains. Ti-plasmid containing isolates represented less than 1% of the A. tumefaciens population. By combining direct soil-DNA extraction with real time PCR, populations of both virulent and avirulent cells were estimated with limits of detection at 20 CFU/g soil. The use of culture independent population estimates versus estimates by dilution plating on selective media in the examination of A. tumefaciens ecology under field conditions will be discussed. Crown gall disease caused by the bacterium Agrobacterium tumefaciens causes significant economic loss in commercial walnut orchards and nursery operations in California. To aid in development of disease control strategies, it is important to understand the structure and dynamics of A. tumefaciens populations in soil. Here we report on the seasonal variation of pathogenic and non-pathogenic A. tumefaciens strains in soil around both diseased and healthy trees using culture based and culture-independent methods. Soil samples were collected monthly and A. tumefaciens was enumerated on 1A containing tellurite with populations ranging from 10⁴ to 10⁶ CFU/g over the sample period. Using Ti-plasmid and chromosomal-specific primers, randomly selected colonies on 1A-tellurite were subjected to PCR based screening to identify virulent and avirulent strains. Ti-plasmid containing isolates represented less than 1% of the A. tumefaciens population. By combining direct soil-DNA extraction with real time PCR, populations of both virulent and avirulent cells were estimated with limits of detection at 20 CFU/g soil. The use of culture independent population estimates versus estimates by dilution plating on selective media in the examination of A. tumefaciens ecology under field conditions will be discussed. Crown gall disease caused by the bacterium Agrobacterium tumefaciens causes significant economic loss in commercial walnut orchards and nursery operations in California. To aid in development of disease control strategies, it is important to understand the structure and dynamics of A. tumefaciens populations in soil. Here we report on the seasonal variation of pathogenic and non-pathogenic A. tumefaciens strains in soil around both diseased and healthy trees using culture based and culture-independent methods. Soil samples were collected monthly and A. tumefaciens was enumerated on 1A containing tellurite with populations ranging from 10⁴ to 10⁶ CFU/g over the sample period. Using Ti-plasmid and chromosomal-specific primers, randomly selected colonies on 1A-tellurite were subjected to PCR based screening to identify virulent and avirulent strains. Ti-plasmid containing isolates represented less than 1% of the A. tumefaciens population. By combining direct soil-DNA extraction with real time