Graduate Thesis Or Dissertation
 

Transmission of plant pathogenic bacteria and a bacteriophage of Agrobacterium tumefaciens (Smith and Townsend) Conn by a saprozoic nematode, Diplogaster lheriteiri Maupas

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  • A saprozoic nematode, Diplogaster lheriteiri Maupas 1919, was studied to determine its relationship to the plant pathogenic bacteria, Agrobacterium tumefaciens (Smith and Townsend) Conn., Erwinia amylovora (Burrill) Winslow et al., Erwinia carotovora (Jones) Holland, Pseudomonas phaseolicola (Burk. ) Dows., Xanthomonas campestris (Pam. ) Dows. and to a phage of A. tumefaciens. The nematodes were allowed to feed on these bacteria and the phage as they grew on nutrient agar plates. It was determined qualitatively and quantitatively that viable bacteria and phages were present in the alimentary canal of the nematodes. The transmission of viable bacteria and phages by the carrier nematodes also were evident in this investigation. Diplogaster lheriteiri is highly tolerant to the toxic action of chlorine as compared with the tested bacteria and phage. The nematodes survived 20 ppm of chlorine in a 40 minute treatment while none of the bacteria or the phage survived in three ppm of chlorine in a two minute contact. Surface sterilization of nematodes by immersing them in a solution of 20 ppm of chlorine for 20 minutes was adequate to eliminate all tested bacteria and phage contaminants. The results of this investigation indicate that D. lheriteiri is capable of ingesting the bacteria, A. tumefaciens, E. amylovora, E. carotovora, P. phaseolicola and a phage of A. tumefaciens. It appeared that a bacterium X. campestris is not a suitable host for the nematodes since they could not multiply in nutrient agar plates containing this bacterium. These ingested plant pathogenic bacteria survived passage through the alimentary canal of the nematode and subsequently formed colonies when plated on nutrient agar. Phages also survived passage through the alimentary canal. The excreted phages were able to lyse the host bacterium when the carrier nematodes were allowed to excrete phages in the nutrient agar plates containing A. tumefaciens. Quantitative studies of bacteria and phage in D. lheriteiri indicated that each female carried approximately 46,200 viable cells of A. tumefaciens. Male nematodes carried fewer bacteria, approximately 9,900 cells. D. lheriteiri was found to carry a smaller number of A. tumefaciens phage particles as compared to the number of bacterial cells. Each female nematode carried an average of 6,965 particles while males carried 1,482 particles. The larger size and appetite of the female were responsible for their effectiveness in carrying more bacteria and phage particles than the males. There was evidence of retention and transmission of bacteria and phage by D. lheriteiri. Transmission of A. tumefaciens and P. phaseolicola occurred up to 27 hours and of E. amylovora and E. carotovora up to 21 hours after feeding by female nematodes. Male nematodes transmitted all tested bacteria up to nine hours after feeding. In the case of A. tumefaciens phage, transmission was detected within 15 hours after feeding in females and nine hours in males if the nematodes were kept under starvation. If phage carrier nematodes were allowed to feed continuously on a non-lysed bacterium (Erwinia carotovora), transmission occurred in shorter periods of nine and six hours in female and male nematodes respectively. This investigation proved that the saprozoic nematode, D. lheriteiri served as a reservoir and a transmitter of certain plant pathogenic bacteria and phage. The nematode may be an important agent in carrying and spreading plant diseases. The ingested plant pathogenic bacteria and phages could survive chlorination which was very harmful to the exposed pathogens. This indicated that the nematode also protects ingested bacteria and phages from toxic chemicals and possibly other adverse conditions. This phenomenon may be important when bactericides or other chemicals are applied to control bacterial plant diseases. Ingested pathogens may survive chemical and cultural control procedures and the nematodes would be available to disseminate and excrete pathogens.
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