Impact of Melatonin Application on Wheat Agronomic Traits Under Abiotic Stress: A Meta-Analysis

This meta-analysis assesses the effects of melatonin (Mel) on various wheat agronomic traits, revealing significant heterogeneity and potential publication bias. This comprehensive analysis highlights the variability across studies (I² > 98% for overall, leaf area, root and shoot weight), indicating a potential for selective reporting in the analysed studies. Grain yield and root weight showed I² values of 93.78% and 99.54%, respectively, confirming the complex nature of melatonin's impact, which necessitates the use of random-effects models. Notably, the study uncovers significant heterogeneity in wheat traits (p < 0.05). Mel increased grain yield by 33.50% and positively influenced root and shoot weights compared to control (no melatonin; nMel). However, the effects varied across different Mel concentration, application method and environmental stressors. Grain yield significantly increased with Mel application, particularly in foliar spray by 41.40%, compared to nMel. Mel consistently enhanced the overall response ratio (lnRR) of grain yield, grain weight, root length, shoot length, leaf area, plant height, shoot weight and root weight by 33.50%, 24.01%, 21.28%, 32.99%, 36.33%, 15.94%, 22.14% and 20.86% compared to nMel. Compared to nMel, the most pronounced grain yield was observed in Mel under salt stress conditions. The benefits of Mel were more pronounced in Egypt, where grain yield increased by 52.91%, suggesting that local environmental factors significantly influence its efficacy. Its impact varied across different cultivars, with Jimai_22 increased root length by 70.83% and Sids_14 by 56.39% compared to nMel, emphasising the importance of genetic factors. Mel application under salt and Cd stress conditions increased root weight by 336% and 470%, respectively, while decreased by 87% under waterlogging compared to no stress conditions. This indicates that Mel greatly increased plant resistance to abiotic stresses by modulating stress-responsive pathways and improving agronomic traits.