Contrasting Effects of Grass-Derived Endophytic Fungal VOCs on Early Growth of Spring Barley and Red Clover: From Stimulation to Suppression

Endophytic fungi can influence plant development through diverse molecular mechanisms; however, their volatile organic compound VOC-mediated effects on agriculturally relevant crops remain insufficiently characterized. In this study, we examined the effects of VOCs produced by six grass-root-associated endophytic fungi—Cadophora fastigiata, Cordyceps fumosorosea, Chaetomium funicola, Epicoccum nigrum, Microdochium bolleyi, and Plectosphaerella cucumerina—on early growth of spring barley (Hordeum vulgare) and red clover (Trifolium pratense). In plate-in-plate VOC exposure assays, we assessed root system traits, root hair formation, and biomass accumulation. Responses to fungal VOCs were fungal species-specific but similar across barley and red clover. VOCs emitted by C. fastigiata and P. cucumerina were consistently associated with increased root growth, root hair proliferation, and seedling biomass, whereas VOCs from M. bolleyi and C. funicola resulted in neutral or growth-suppressing effects. A complementary seed inoculation experiment was conducted with barley, which showed fungal species–dependent contrasting effects consistent with the observations of VOCs treatment. Gas chromatography–mass spectrometry (GC–MS) analysis revealed that C. fastigiata, the isolate associated with the strongest growth-promoting responses, emitted a diverse VOC profile dominated by sesquiterpenes, with 22 compounds identified. Together, these results demonstrate that VOCs emitted by grass-root-associated endophytic fungi exert reproducible, species-specific effects on early plant development occurring in phylogenetically distant species. The findings highlight the value of VOC-based assays for comparative functional screening of fungal isolates, providing a foundation for future studies that aim to link individual VOCs to plant growth responses.