Taxonomic diversity of bacteria associated with the roots of modern, recent and ancient wheat cultivars
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Breeding programs for crop plants are designed to improve agronomic characteristics such as yield, fertilizer use efficiency and disease resistance. These programs do not typically consider interactions between plants and soil microflora. This study assessed the bacterial communities associated with roots of various spring wheat (Triticum spp.) cultivars of related lineage. Bacteria (n=ca. 1900) were isolated from the rhizosphere and root interior of Triticum moncoccum PI 167549 (an ancient land race that originated in Turkey), T. aestivum cv. Red Fife (historical spring wheat cultivar released in Canada ca. 1845) and T. aestivum cv. CDC Teal (modern cultivar registered in Canada in 1991) grown at two different field sites. Bacteria were identified by gas chromatography-MIDI (microbial identification software) fatty acid methyl ester analysis. Twenty-eight bacterial genera were identified as being associated with the three wheat cultivars, but only Aureobacter species differed significantly between cultivars with 16 isolates identified from the root interior of PI 167549 compared to one isolate from Red Fife and two from CDC Teal. In contrast, the bacterial endophytic community of the more modern cultivars was more diverse than that seen for the ancient land race. Increases in diversity were not limited to a single genus and some species were selected against. For example, pseudomonads were more numerous and diverse in the root interior (11 species identified in 117 isolates) compared to the rhizosphere (eight species identified in 94 isolates), but Pseudomonas fluorescens abundance decreased in the root interior compared to the rhizosphere. The fact that the roots of newer wheat cultivars were aggressively colonized by endophytic pseudomonads suggests that these bacteria might be exploited as plant growth-promoting rhizosphere bacteria or as a means to establish specific catabolic activities in these plants.
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