Submitted to: American Phytopathology Society
Publication Type: Abstract Only
Publication Acceptance Date: 6/20/2005
Publication Date: N/A
Technical Abstract: Biocontrol isolates of Pseudomonas fluorescens that produce the antifungal metabolite 2,4-diacetylphloroglucinol (DAPG) can suppress soilborne pathogens, but the efficacy of the isolates depends partially on external factors. As part of a long-term research program to identify the genes and pathways in wheat that govern its interaction with biocontrol pseudomonads, we quantified steady-state levels of DAPG produced by two isolates of P. fluorescens on the roots of three Triticum aestivum L. (hexaploid wheat) cultivars four days after seed inoculation and growth in Petri plates. Both bacterial isolates aggressively colonized wheat roots, and produced DAPG. However, isolate Q8r1-96 produced more metabolite in culture and persisted in the wheat rhizosphere longer than Q2-87. As expected, accumulation of DAPG on roots of all three cultivars occurred at higher levels following colonization with Q8r1-96, compared to Q2-87. However, there was a striking differential in metabolite production by Q8r1-96 and Q2-87 on cv. Tara, whereas the differential on cv. Buchanan was much smaller. The accumulation patterns were not attributed to differences in rhizoplane population densities; both isolates reached an average of 2.0 x 109 colony-forming units g-1 after four days, regardless of the cultivar. Previous studies have shown that steady-state levels of DAPG are correlated to the extent of root colonization in a host species-dependent manner. Our findings indicate that DAPG accumulation in the wheat rhizoplane is dependent on an interaction between cultivar and bacterial genotypes. Progress in identifying the determinants of differential accumulation will be presented.