Microbiome-Assisted Heat Resilience in Cereals: Direct Evidence from Rice Endophytes, Comparative Stress Ecology, Nutrient Management, and Field-Validation Priorities

Rising temperatures threaten cereal productivity through reproductive injury, altered carbon balance, and changes in water and nutrient availability. This critical narrative review evaluates whether cereal-associated microbes, especially bacterial endophytes, can moderate these effects. Direct experimental evidence for microbial protection against imposed heat is concentrated in rice and largely derives from controlled-environment and pot experiments; observations from drought-stressed rice, sorghum, and other grasses provide indirect insights into microbial assembly but do not establish thermotolerance. We distinguish microbial screening traits and associated plant biomarkers (biological plausibility) from perturbation-based mechanism tests (causal support) and replicated field grain-yield outcomes (agronomic validation). We integrate reproductive-stage risk, nutrient-management interactions, and a staged screening-to-field framework with measurable performance and economic criteria. Promising rice experiments report changes in growth, oxidative-stress biomarkers, and grain weight per panicle, but these endpoints must not be generalized to multi-location field yield protection. Priority gaps include flowering-stage heat experiments, colonization and mechanism tests, fertilizer-response interactions, and replicated trials across genotypes, seasons, and sites. Microbiome interventions should therefore be considered candidates for integrated adaptation, not established cross-cereal heat-resilience solutions.