Responses of arbuscular mycorrhizal wheat to salinity: from symbiotic signaling to stress adaptation

Salinity is a major constraint to wheat productivity, imposing osmotic stress, ionic imbalance, and oxidative pressure that compromise growth and yield. Arbuscular mycorrhizal fungi can improve wheat performance under salinity through effects extending beyond nutrient acquisition. This review examines the context-dependent symbiosis between wheat and arbuscular mycorrhizal fungi, in which reciprocal signaling and resource exchange influence stress adaptation. Direct studies, particularly in durum and bread wheat, indicate that AM colonization can improve K⁺/Na⁺ balance, nutrient acquisition, water relations, membrane stability, antioxidant regulation, osmoprotectant metabolism, and stress-responsive gene expression. By contrast, detailed mechanisms of presymbiotic communication, fungal-signal perception, nuclear Ca2+ decoding, transcriptional accommodation, arbuscule development, and plant-to-fungus lipid transfer have been characterized mainly in AM model plants and other cereals. These conserved pathways provide a mechanistic framework for interpreting, rather than presuming, their operation in salt-stressed wheat. Integrating these evidence levels indicates that AM-associated benefits arise from coordination among ion and water transport, reactive oxygen species and redox regulation, hormonal crosstalk, carbon allocation, and arbuscule-mediated nutrient exchange rather than from enhancement of a single protective trait. The magnitude and nature of these benefits are context-dependent, influenced by wheat genotype, fungal identity, salinity intensity, nutrient status, and carbon cost-benefit trade-offs. We identify priorities for wheat-specific functional validation, spatial and temporal analysis of Ca2+, reactive oxygen species, hormones, and transport processes, genotype-fungus matching, and multi-environment field assessment. This evidence-aware framework can support microbiome-informed breeding, targeted inoculant development, and integrated management of wheat in salt-affected agroecosystems.

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