Characterizing the devastating rice blast fungus, Sagnaporthe oryzae and a potential biocontrol agent, Bacillus velezensis strain S4

Abstract

Plant diseases caused by fungal pathogens cause severe problems for agriculture as they greatly reduce crop yield, with some species causing up to 100% crop loss. Managing these fungal plant pathogens are of the utmost importance as the global economy and crop production relies heavily on cereal crops such as wheat, rice, maize and barley. Traditional methods in mitigating fungal pathogens, typically including fungicides, are ineffective against certain pathogens that have developed resistance, an example of this being the rice blast fungus, or Magnaporthe oryzae. M. oryzae kills enough rice to feed 60 million people per year, and thus has become a focal point in the field of plant pathology, where it is regarded as a model organism. Since the usage of fungicides in this instance is not effective, scientists must look for alternatives and now favor the use of biological control agents (BCAs), an environmentally friendly way of disease management. Common BCAs are found within the bacterial genus, Bacillus, which act as a plant growth promoting bacteria (PGPB). Bacillus velezensis strain S4 was isolated and sequenced from biochar-amended agricultural soil in Delaware. Upon genomic analysis and plate assays, B. velezensis strain S4 putatively encodes antifungal compounds, and enzymes including cellulases and proteases. M. oryzae in the presence of B. velezensis strain S4 displays hyphal lesions, reduced radial growth, and decreased appressorium formation, all of which could affect its pathogenicity. RNASeq analysis of this bacterial-fungal interaction revealed 69 differentially expressed genes (DEG) in M. oryzae, including toxin biosynthesis. All together B. velezensis strain S4 shows potential as a BCA for M. oryzae; observing specific aspects of this interaction could yield more insight into how fungi defend themselves against bacteria.