Rice blast fungus, Pyricularia oryzae Cavara, is an important disease causing significant yield loss for rice production in USA as well as Thailand. To control this fungus, biological control is an important potential alternative practice according to its environmentally friendly and no risk to human health. Research on the use of antagonistic microorganisms to control rice blast disease was conducted at Louisiana State University, USA during October 2014 to September 2015. In vitro screening of antagonistic bacteria against P. oryzae using dual culture method found that Bacillus amyloliquefaciens RAB14R showed the highest activity of growth inhibition to the pathogenic fungus. The survival of antagonistic bacteria in bacterial formulation was highest when mixed with 5% sucrose during freeze-drying. In the field condition, antagonistic bacterial suspension was sprayed to rice plants at the tillering and heading stages. For cv. M202 (a highly susceptible cultivar), all the treatments of antagonistic bacteria suppressed the disease less effectively than fungicide application. For rice cv. CL151 (susceptible cultivar), there were no differences among the treatments for the control of leaf blast. In the control activity for panicle blast, all the treatments of antagonistic bacteria showed some disease suppression activities compared to the water control but their activities were less than that of fungicide application.
Genetic elements for the antagonistic activity of RAB14R were identified by using a Tn5 mutagenesis technique. The result indicated that two genes encoding urocanate hydratase and diguanylate cyclase were associated with the growth inhibition of P. oryzae.