Mitigation of chilling and freezing stresses through colonization with arbuscular ‎mycorrhizal fungi in spring barley ‎

Cold stress is an ‎important limiting factor for cereal production. Barley is a host species for arbuscular mycorrhizal fungi (AMF) with a high genetic diversity in response to cold stress. In order to explore the mechanisms for the ameliorative effect of AMF under cold stress, an experiment was undertaken using completely randomized block design with three factors including temperature treatment, AMF inoculation and plant cultivar. Two spring barley cultivars with different cold tolerance (‘Reyhan’ as tolerant and ‘Torkaman’ as susceptible) were inoculated with two AMF species (Diversispora versiformis and Rhizophagus irregularis) and grown under chilling (CH, 5 °C) and freezing (FR, ‒5 °C) temperatures for three weeks. Dry matter production, photosynthesis rate, and membrane ‎integrity parameters decreased, while the antioxidant defense and the synthesis of phenolics ‎were activated under CH stress. Inoculation of plants with AMF alleviated the adverse ‎effects of CH stress on growth and membrane parameters, while exacerbated CH effect on ‎the antioxidant system and phenolics accumulation. Plants could not survive FR stress when ‎they were not cold acclimated through prior exposure to CH treatment, unless they were ‎inoculated with AMF which results in survival rates almost similar to cold-acclimated plants. Our results suggested that AMF alleviated CH stress through ‎reducing H2O2 and improving membrane integrity while the ‎substituting effect of AMF for cold acclimation and increasing FR survival was mediated by the activation of antioxidant ‎defense and phenolics synthesis and accumulation of proline.