Mung bean, a legume, is sensitive to abiotic stresses at different growth stages, and its yield potential is affected by drought and high-temperature stress at the sensitive stage. Melatonin is a multifunctional hormone that plays a vital role in plant stress defense mechanisms. This study aimed to evaluate the efficiency of melatonin under individual and combined drought and high-temperature stress in mung bean. An experiment was laid out with five treatments, including an exogenous application of 100 µM melatonin as a seed treatment, foliar spray, and a combination of both seed treatment and foliar spray, as well as absolute control (ambient condition) and control (stress without melatonin treatment). Stresses were imposed during the mung bean’s reproductive stage (31–40 DAS) for ten days. Results revealed that drought and high-temperature stress significantly decreased chlorophyll index, Fv/Fm ratio, photosynthetic rate, stomatal conductance, and transpiration rate through increased reactive oxygen species (ROS) production. Foliar application of melatonin at 100 µM concentration enhanced the activity of antioxidant enzymes such as superoxide dismutase, catalase, and ascorbate peroxidase and the concentration of metabolites involved in osmoregulation and ion homeostasis; thereby, it improves physiological and yield-related traits in mung bean under individual and combined stress at the reproductive stage.

Biostimulants are innovative organic tools, which promote the growth, plant development, production, and quality of various crops without harming the environment; however, the effects of biostimulants on the production of tomato needed to be explored further under open field conditions. Based on this view, this study’s objective was to assess the impact of Kendal Root, a biostimulant-containing seaweed, Ascophyllum nodosum, and plant extracts on the phytomorpho-physiological, yield, and quality of tomato. Three doses of Kendal Root (2.5, 5.0, and 10 L ha⁻¹) were given as soil drenching, and the results were compared with control. Generally, the Kendal Root treatments positively improved the growth, physiological, yield, and quality attributes of tomato. However, among the three different concentrations, Kendal Root 5.0 L ha⁻¹ significantly improved the plant growth and physiological aspects of tomato, such as plant height, leaf area, shoot and root dry weight, SPAD value, and gas exchange parameters. Considering the yield traits, the Kendal Root 5.0 L ha⁻¹ application significantly improved the tomato fruit number, yield per plant, and yield per hectare. Conversely, flower number per plant and average fruit weight was not remarkably improved by Kendal Root 5.0 L ha⁻¹. Moreover, Kendal Root 5.0 L ha⁻¹ positively improved the quality traits of tomato, including total soluble solids, ascorbic acid content, lycopene, and total sugars than the titratable acidity content of tomato fruits. Hence, the integration of Kendal Root biostimulant in tomato production could be an effective way to boost plant growth, production, and quality of tomato.

In recent years, environmental stresses viz., drought and high-temperature negatively impacts the tomato growth, yield and quality. The effects of combined drought and high-temperature (HT) stresses during the flowering stage were investigated. The main objective was to assess the effects of foliar spray of melatonin under both individual and combined drought and HT stresses at the flowering stage. Drought stress was imposed by withholding irrigation, whereas HT stress was imposed by exposing the plants to an ambient temperature (AT)+5°C temperature. The drought+HT stress was imposed by exposing the plants to drought first, followed by exposure to AT+5°C temperature. The duration of individual and combined drought or HT stress was 10 days. The results showed that drought+HT stress had a significant negative effect compared with individual drought or HT stress alone. However, spraying 100 µM melatonin on the plants challenged with individual or combined drought and HT stress showed a significant increase in total chlorophyll content [drought: 16%, HT: 14%, and drought+HT: 11%], F_v/F_m [drought: 16%, HT: 15%, and drought+HT: 13%], relative water content [drought: 10%, HT: 2%, and drought+HT: 8%], and proline [drought: 26%, HT: 17%, and drought+HT: 14%] compared with their respective stress control. Additionally, melatonin positively influenced the stomatal and trichome characteristics compared with stress control plants. Also, the osmotic adjustment was found to be significantly increased in the melatonin-sprayed plants, which, in turn, resulted in an increased number of fruits, fruit set percentage, and fruit yield. Moreover, melatonin spray also enhanced the quality of fruits through increased lycopene content, carotenoid content, titratable acidity, and ascorbic acid content, compared with the stress control. Overall, this study highlights the usefulness of melatonin in effectively mitigating the negative effects of drought, HT, and drought+HT stress, thus leading to an increased drought and HT stress tolerance in tomato.