Evaluation of endophytic bacterial strains as antagonists of take-all in wheat caused by Gaeumannomyces graminis var. tritici in greenhouse and field

Six endophytic bacterial strains from wheat roots, selected from extensive screening tests, were studied in greenhouse pot experiments against take-all disease of wheat, caused by Gaeumannomyces graminis var. tritici (Ggt). For comparison, the fungicide triadimefon was included. All six bacterial strains and triadimefon significantly reduced take-all in wheat plants between 39.4 and 57.3% compared to the inoculated control. Treatment with the bacterial strains also significantly increased growth parameters of roots (e.g., average length, fresh, and dry weight) in comparison with the inoculated control. One of the endophytic bacterial strains, designated EDR4, which proved to be most consistent in further greenhouse tests, was also examined in field trials against take-all in wheat. In the field experiment 2006/2007, height of wheat plants in Ggt inoculated plots was significantly reduced compared to the non-inoculated treatments. Yield parameters such as kernels per head and thousand kernel weight (TKW) in the inoculated control were lower compared to other treatments. In the inoculated plots, individual treatments with the strain EDR4 increased yield compared to the inoculated control. In the field trial 2007/2008 treatments with strain EDR4 as well as the fungicide triadimefon reduced take-all by 49.6 and 61.9%, respectively, compared to the inoculated control. At harvest, in the inoculated control plant height, seeds per head and TKW were significantly lower compared to the other treatments. Treatments with EDR4 eliminated the detrimental effects of take-all on grain yield to a similar degree as triadimefon application. The strain EDR4 distinctly inhibited growth of Ggt in vitro and was identified as Bacillus subtilis on the basis of its morphology and 16S rRNA sequence analysis as well as physiological and biochemical characteristics. These results indicate that the strain EDR4 has potential in directly controlling take-all disease of wheat.