IBUN2755 Bacillus strain controls seedling root and bacterial panicle blight caused by Burkholderia glumae

Abstract

Burkholderia glumae is the causal agent of seedling rot and bacterial panicle blight in rice. It has a worldwide distribution in most rice producer countries generating crop losses of up to 75%. Currently, there is no known effective control for this pathogen. In this study 74 Bacillus strains isolated from the rhizosphere of different plants were evaluated under in vitro conditions against three strains of B. glumae. Twenty-six strains of Bacillus were selected for their antagonistic activity and then were evaluated in plantae under the two different inoculation sources of B. glumae: the seeds, and the substrate, since these are the two main reservoirs of the pathogen in the field. Inoculated seeds with the selected Bacillus strains were planted in a previously inoculated substrate with B. glumae, finding that 11 strains showed a reduction of the infection up to 63.5%. When evaluating the biological control activity of those 11 Bacillus strains in B. glumae infested seeds, four strains (IBUN12A04, IBUN16A08, IBUN2755 and IBUN15A09), showed disease reduction of up to 62.4%. These four strains were again evaluated under greenhouse conditions with seeds infested with B. glumae to determine the presence of the pathogen in asymptomatic plants 10 and 30 days after germination. In this case, Bacillus strains reduced the population of B. glumae in the plant up to two orders of magnitude in relation to disease control, and some even promoted plant growth in relation to an uninoculated control. Finally, the IBUN 2755 strain, which showed the highest biocontrol activity in the greenhouse, was evaluated under field conditions, showing a significant reduction in the symptoms of the disease and an increase in crop yield of up to two tons per hectare with relation to the uninoculated control.