Volatile organic compound profiles in oat are shaped by arbuscular mycorrhizal fungi, barley yellow dwarf virus and soil herbicide residues

Volatile organic compounds (VOCs) are emitted by plants and vary in quantity and composition depending on biotic and abiotic environmental conditions. Plant-emitted VOCs are altered by attacking herbivores and pathogens, and have been increasingly found to be fine-tuned by microbial associates and environmental pollutants. Here, we studied whether arbuscular mycorrhizal fungi (AMF) treatment, barley yellow dwarf virus (BYDV) infection, and soil pollution with glyphosate-based herbicide (GBH) residues affect the emission of volatile organic compounds by oat (Avena sativa) plants. Oat plants were grown in a common garden study in southwestern Finland, where seeds in half of the plots had received a dressing with AMF inoculant before being sown in plots with a history of regular glyphosate application and control plots without a history of glyphosate use. During the study, an average of 30% of the oat plants showed symptoms of infection by BYDV, which was then included as a treatment. We collected plant VOCs of eight plants per treatment via headspace sampling with subsequent analysis by gas chromatography coupled to mass spectrometry (GC-MS). The percentage of BYDV-infected plants did not differ between AMF-treated and untreated plants, nor between plants growing in glyphosate-polluted and glyphosate-free soil. The emission of VOCs displayed characteristic profiles depending on the soil GBH history, BYDV infection, and AMF seed treatment. In particular, AMF treatment caused an increase in the terpenoid (E)-β-ocimene, and the fatty acid derivatives 1-octen-3-ol and octanal. Virus infection reduced the emission of octanal and induced the emission of the terpenoids (E)-caryophyllene and β-farnesene. GBH-treated soil caused an increase in the emission of green leaf volatiles (Z)-3-hexen-1-ol, 1-hexanol, and (Z)-3-hexenyl-acetate compared to plants in control soil. Plant-emitted VOCs displayed a distinct pattern elicited by viral infection, fungal-root association, and herbicide pollution in soil, indicating the impact of biotic and abiotic factors on the plant's biology. While the biological mechanisms behind the distinct VOC profiles remain speculative, the results indicate that VOC emission patterns may be utilized to infer plant and soil health status in crop production.