Poster: Plant-pathogen interactions

Abs # 576: Diversity of endophytic bacteria in healthy and Ralstonia solanacearum infected tobacco seedlings.

Presenter:	Bottomly-Tennison, Sarah A, sbottom@clemson.edu
Authors	Bottomly-Tennison, Sarah A (A)   Fortnum, B  (A)   Kurtz, H  (A)   Kluepfel, D  (B)
Affiliations:	(A): Clemson University (B): UC Davis

Endophytic bacteria were isolated and identified from healthy greenhouse grown tobacco (Nicotiana tabacum cv K326 and K346) plants grown in non-sterile field soil. Five plants were destructive sampled every 7 days over a 3-month period to examine the microbial community present within the vascular tissue. After surface sterilization the plant tissue was ground in chilled PBS, serially diluted, plated onto TSBA+cyclohexamide and incubated at 28C. Colonies were counted after 72 hr and cfu/g tissue determined. Randomly selected colonies from isolation plates were identified using FAME/MIDI (fatty acid methyl ester) analysis. In field experiments, endophytic bacteria were isolated from tobacco plants grown in soil inoculated with Ralstonia solanacearum and from plants grown in untreated soil. In the greenhouse and field trial, as the plants aged, the diversity of the microbial community in the vascular tissue increased. The Gram-positive bacterium Bacillus sp. dominated the vascular tissue with Pseudomonas sp. also comprising a major component of the community. However, in the field trial at DAY 112-post plant, populations of the Gram-negative bacterium Pseudomonas sp. equaled those of the Gram-positive bacterium Bacillus spp. In the field trial, the number of bacteria present per gram of tissue in tobacco plants consistently increased across all sample dates and treatments. Endophytic bacterial communities varied between the resistance and susceptible cultivar based on a total community analysis (fatty acid methyl ester). RFLP molecular analysis of the bacterial communities confirmed a varietal effect on bacterial populations.