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Title: The role of bacterial communities in the natural suppression of Rhizoctonia bare patch of wheat Triticum aestivum L

item YIN, CHUNTAO - Washington State University
item HULBERT, SCOT - Washington State University
item SCHROEDER, KURTIS - Washington State University
item MAVRODI, OLGA - Washington State University
item MAVRODI, DMITRI - Washington State University
item DHINGRA, AMIT - Washington State University
item SCHILLINGER, WILLIAM - Washington State University
item Paulitz, Timothy

Submitted to: Applied and Environmental Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/20/2013
Publication Date: 12/20/2013
Citation: Yin, C., Hulbert, S.H., Schroeder, K.L., Mavrodi, O., Mavrodi, D., Dhingra, A., Schillinger, W.F., Paulitz, T.C. 2013. The role of bacterial communities in the natural suppression of Rhizoctonia bare patch of wheat Triticum aestivum L. Applied and Environmental Microbiology. 79:7428-7438.

Interpretive Summary: We observed a natural suppression of Rhizoctonia bare patch in a long-term cropping system study. The patch intensity reached a peak 7 years after no-till was adopted, but then declined by year 11. We sampled soil and rhizosphere inside of active patches, outside of the patches in healthy areas, and in patches that disappeared over time. Using pyrosequencing, we identified genera in the Bacteroidetes (Flavobacterium and Chryseobacterium) and Oxalobacteraceae that were more predominant on diseased rhizospheres and may be involved in suppression. We duplicated the shifts in bacteria communities in greenhouse experiments, and tested isolates of Chryseobacterium which suppressed Rhizoctonia disease on seedlings.

Technical Abstract: Rhizoctonia bare patch and root rot of wheat, caused by Rhizoctonia solani AG-8, develops as distinct patches of stunted plants, and limits the yield of direct-seeded wheat in the Pacific Northwest (PNW) of the United States. At a long-term wheat cropping systems study site near Ritzville, WA, converted from conventional tillage to direct-seeding in 1997, bare patch first appeared in year 3, reached a peak in year 7, then declined to near zero by year 11. Bacterial communities from bulk and rhizosphere soil of plants from inside of patches, outside of patches, and recovered patches, were analyzed by pyrosequencing with primers designed to the 16S rDNA. OTUs of Acidobacteria and Gemmantimonas were in higher frequency in the rhizosphere of healthy plants outside of patches, compared to diseased plants from inside of patches. Dyella and Acidobacteria Gp7 had higher frequencies in recovered patches. Chitinophaga, Pedobacter, Oxalobacteriaceae (Herbaspirillum, Dunganella and Massilia) and Chyseobacterium were higher in the rhizosphere of diseased plants from inside of patches. For selected taxa, trends were validated by real-time quantitative PCR, and shifts of frequency in the rhizosphere over time were duplicated with cycling experiments in the greenhouse, with successive plantings of wheat in Rhizoctonia-inoculated soil. Chryseobacterium soldanellicola was isolated from the rhizosphere inside of patches and exhibited significant antagonism against R. solani AG 8 in vitro and in greenhouse tests. In conclusion, this study identified novel bacterial taxa which respond to conditions affecting bare patch symptoms and may be involved in suppression of Rhizoctonia root rot.