Genetic and environmental regulation of arbuscular mycorrhizal responsiveness in petunia : Implications for breeding and trait selection

Arbuscular mycorrhizal (AM) fungi enhance plant nutrition and stress tolerance, yet their agricultural use remains limited because symbiotic outcomes are unpredictable. Mycorrhizal responsiveness (AM-responsiveness)-the host's growth response to AMF inoculation-offers a potential breeding target. We investigated variation in AM-responsiveness among Petunia hybrida, P. axillaris, P. exserta and P. inflata, and explored its genetic and environmental determinants. Plants were inoculated with Rhizoglomus irregulare and analysed for biomass, AMF colonization, phosphate uptake, phosphate transporter expression and accumulation of the foliar biomarker 11-carboxyblumenol C-glucoside. Species differed strongly in colonization intensity, biomass and biomarker accumulation. Based on contrasting AM-responses between P. axillaris and P. exserta, a recombinant inbred line (RIL) population derived from these parents was used to assess AM-responsiveness as a quantitative trait under variable environmental conditions. The RILs showed transgressive segregation for biomass responses, confirming a heritable component, while strong genotype × environment (G × E) interactions demonstrated environmental dependency. These results highlight AM-responsiveness as a genetic trait suitable for breeding but emphasize the need to account for environmental variation. Foliar blumenols proved effective non-destructive indicators of colonization, supporting their potential in high-throughput screening for mycorrhizal traits.