Submitted to: Biological Control
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/12/2003
Publication Date: 12/22/2003
Citation: Okubara, P.A., Kornoely, J.P., Landa, B.B. 2003. Rhizoshpere colonization of hexaploid wheat by pseudomonas fluorescens strains q8r1-96 and q2-87 is cultivar-variable and associated with changes in gross root morphology.. Biological Control 30 (2004) 392-403. Interpretive Summary: Cultivar-variable root colonization by Pseudomonas fluorescens strain Q8r1-96 in Triticum aestivum (hexaploid wheat) All Pacific Northwest (PNW) varieties of wheat (2.44 million acres) and barley (370,000 acres) sustain 10 to 15% yield losses due to soil-borne fungal diseases, such as take-all, Pythium root root, and Rhizoctonia root rot/damping off. These losses can reach 60% with the practice of direct seeding. Suppression of root pathogens by naturally-occurring soil bacteria offers an alternative to chemical control and supports the trend towards sustainable agriculture. A comprehensive understanding of the role of the plant in disease suppression is needed to improve the efficacy of disease-suppressive microbes. In a survey of 28 PNW wheat varieties, we have found differences amongst them with respect to their ability to maintain high levels of a take-all suppressive Pseudomonas in or around the roots. These differences were correlated to root surface area, root length, and average root diameter, but no one root factor was associated with all of the differences. These findings suggest that host genes are involved in governing interactions with take-all suppressive Pseudomonas, and that more than one gene is likely to be required for the interaction.
Technical Abstract: Host genes are likely to have a significant impact on the quality and extent of interactions with microbes in the phyllosphere, spermosphere and rhizosphere. We are seeking to understand host pathways that govern the three-way interaction between necrotrophic root pathogens, the bacterial biological control agent Pseudomonas fluorescens, and their host Triticum aestivum (hexaploid wheat). To examine naturally-occurring host varitation, we have surveyed 28 Pacific Northwest (PNW) wheat cultivars for the ability to undergo rapid root colonization with the aggressive P.fluorescens strain Q8r1-96 than Q2-87 within 14 days of planting in non-pateurized, non-agricultural soil. Colonization levels normalized to root weight reached maximum steady-state levels within 4 days of inoculation and planting, and higher colonization levels of Q8r1-96 was observed by 7 days in some cases. A principal components analysis showed that root colonization by Q8r1-96 generally was independent of root total length, fresh weight, surface area, or average diameter. Taken together, these results suggest that the outcome of hte wheat-Pseudomonas interaction is variable with respect to cultivar, that there is temporal component to the dynamics of the interaction, and that differential colonization by Q8r1-96 is not correlated with any single root morphometric factor.