Complexity of combined abiotic stresses to crop plants

Abstract

Plants frequently encounter combined abiotic stress factors such as heat and drought, salinity and drought, and flooding and salinity, which impact their growth, development, and productivity. These stress combinations often produce distinct physiological, biochemical, and molecular responses, requiring complex mechanisms for tolerance. We highlight the morphological adaptations (e.g., reduced leaf area, deeper roots) and biochemical responses (e.g., accumulation of osmoprotectants and antioxidants) that help plants mitigate stress effects. We emphasize the role of phytohormones such as abscisic acid, salicylic acid, and ethylene in stress signaling and molecular regulation through transcription factors and epigenetic modifications during combined stresses. Integrating advanced tools like omics technologies (transcriptomics, proteomics, metabolomics), genetic engineering (CRISPR/Cas9), speed breeding, and systems biology provides insights into stress-responsive pathways and accelerates the development of resilient crops. Additionally, nutrient management strategies (notably silicon and lesser essential nutrient supplementation), and agricultural practices like low tillage and cover cropping are also explored as strategies to improve stress tolerance. One of the least studied in combined stresses is the utilization of plant growth-promoting rhizobacteria, either single or mixed communities. These are promising approaches for promoting stress tolerance. This review underscores the need for multi-year field trials and interdisciplinary strategies to address the complexities of combined stresses and achieve sustainable crop productivity under changing climatic conditions. Future perspectives focus on designing climate-smart crops using speed breeding, synthetic biology, and machine learning.