Enhancement of production of pathogen-suppressing volatiles using amino acids

Bacterial volatile organic compounds can play a significant role in antagonistic interactions. Enhancing the production of bacterial volatiles that suppress the growth of soil-borne phytopathogenic fungi, has perspective as a sustainable disease control strategy. In the present study, we explored the potential of stimulating <i>Burkholderia</i> AD24 and <i>Paenibacillus</i> AD87 to produce volatiles that suppress the growth of the plant pathogenic fungi <i>Fusarium culmorum</i> PV and <i>Rhizoctonia solani</i> AG2.2IIIb. We provided the bacterial strains with a mixture of amino acids that can serve as precursor molecules in metabolic routes leading to emission of suppressive bacterial volatiles. Only <i>Burkholderia</i> AD24 was stimulated to produce a volatile blend that led to higher suppression of both pathogens. Subsequent analysis of the volatile composition emitted by <i>Burkholderia</i> AD24 in the presence of amino acids, showed higher abundance of antifungal compounds, including sulfur compounds (DMDS), pyrazines (2,5-dimethyl pyrazine) and carbohydrates (3-methyl-1-butanol). Follow-up trials with single amino acids revealed a pathogen specific response effect. When <i>Burkholderia</i> AD24 was cultivated in the presence of glutamine and asparagine, the emitted volatile blend suppressed the growth of <i>F. culmorum</i>, whereas when cultivated in the presence of glycine, glutamine, arginine and lysine the volatile blend suppressed the growth of <i>R. solani</i>. Analysis of the volatile blend composition showed differences between the amino acid treatments. Our findings show that amino acid precursor molecules can stimulate the production of fungistatic volatiles but the sensitivity of the fungal pathogens to these bacterial volatiles varies. This should be considered in future application strategies.