Melatonin improves high temperature stress tolerance by physiological and reproductive stabilization in common bean

The common bean is an essential legume crop that faces significant productivity threats from high temperature stress (HTS). It negatively impacts physio-biochemical processes, floral organ development, and fertilization, and degrades seed and nutritional quality, leading to yield losses. To alleviate the impact of HTS on common bean genotypes that are tolerant to water deficit stress (WDS), foliar applications (0 and 300 µM) of melatonin (MT), a low-molecular-weight organic compound that acts as both a plant hormone and an antioxidant, was applied at pre and post flowering stage of the crop. Two experiments were conducted to study the efficacy of MT foliar application on common bean genotypes under HTS (I & II) conditions during the late Rabi (post-rainy) season of 2023-24. Foliar application of MT reduced the canopy temperature by 29.1% under HTS-I (29-32 °C) and 7.9% under HTS-II (32-35 °C) and increased the pollen viability by 25.8% and 45.9% under HTS-I and II, respectively. In addition, MT significantly enhanced seed yield, with increases of 11.2% and 34.4% under HTS-I and HTS-II, respectively. MT also increased the micronutrient content of the seeds under HTS. Overall, these results provide a comprehensive understanding of the protective and tolerance effects of MT against HTS, ensuring yield stability in HTS-prone areas.