International Journal of Horticulture, 2025, Vol.15, No.5, 242-256 http://hortherbpublisher.com/index.php/ijh 244 From a physiological standpoint, salt-stressed plants experience an increase in reactive oxygen species (ROS) and membrane lipid peroxidation (Yadav et al., 2011; Hao et al., 2021). Additionally, stomatal regulation becomes compromised, reducing photosynthetic efficiency and carbon assimilation (Li et al., 2024). In fruit-bearing vegetables, like cucumber (Cucumis sativus L) and melon (Cucumis melo L.), salinity stress can hinder normal fruit development, often resulting in misshapen or poor-quality fruits (Joshi et al., 2013; Pinheiro et al., 2019). 2.3 Heat stress The increasing concentration of greenhouse gases in the atmosphere is projected to raise the global average temperature by approximately 1.0 °C-1.8 °C by the end of the 21st century under very low emissions scenarios, or 2.1 °C-3.5 °C under intermediate scenarios, according to recent projections by the Intergovernmental Panel on Climate Change (Lee et al., 2023). In plants, heat stress is defined as a rise in temperature above a critical physiological threshold, sustained over a period of time long enough to cause irreversible alterations in growth and developmental processes (Wahid et al., 2007). High temperatures interfere with the entire physiological machinery of crops. When temperatures exceed critical thresholds (often 35 °C-38 °C), enzymes involved in photosynthesis, respiration and reproductive development begin to denature or lose functionality (Wahid et al., 2007). Pollen tube elongation, ovule fertilization, and embryo development are particularly heat-sensitive stages (Prasad et al., 2017). In tomato (Solanum lycopersicum L.), pepper (Capsicum annuum L.) and eggplant (Solanum melongena L.), this results in reduced fruit set, flower drop and malformed fruits (Abou-Hussein, 2012). Heat stress also accelerates respiration rates, which consumes the sugars produced by photosynthesis and decreases the net energy available for growth and storage in edible parts. Leaf senescence may be triggered prematurely, reducing the effective photosynthetic area (Tan et al., 2023). Furthermore, the synthesis of pigments (e.g., anthocyanins and carotenoids) is suppressed, leading to color defects in fruits such as tomatoes and peppers (Espley and Jaakola, 2023). 2.4 Cold stress Cold stress, including both chilling (0 °C-15 °C) and freezing (<0 °C), affects subtropical and tropical horticultural crops by damaging membranes and inhibiting vital metabolic pathways. During germination, cold conditions delay radicle emergence, reduce uniformity and increase seedling mortality (Aslam et al., 2022). In leafy crops, like lettuce (Lactuca sativa L.), chard (Beta vulgaris L. var. cicla), spinach (Spinacia oleracea L.) and arugula (Eruca vesicaria L.), low temperatures reduce photosynthetic activity and may cause water-soaked lesions and tissue collapse due to ice crystal formation (Zhou et al., 2019; Jahed et al., 2023). These effects are associated with oxidative stress and membrane damage, leading to growth inhibition and yield losses (Devireddy et al., 2021). Chilling-sensitive fruit vegetables such as tomato (Solanum lycopersicum L.), bell pepper (Capsicum annuum L.) and melon (Cucumis melo L.), commonly exhibit symptoms such as interveinal chlorosis, leaf curling, and delayed flowering when exposed to low, non-freezing temperatures (Zhang et al., 2017; Huang et al., 2022). Cold stress also impacts reproductive development by impairing the activity of floral enzymes and limiting pollen tube growth, ultimately reducing fruit set and productivity. The accumulation of soluble sugars, which can offer partial protection, varies greatly by genotype and is often insufficient to prevent injury (Huang et al., 2022). 3 Seed Priming 3.1 Concepts and mechanisms Seed priming is defined as a pre-sowing technique that involves the controlled hydration of seeds to initiate early metabolic processes associated with germination, without permitting radicle protrusion. After hydration, seeds are re-dried to their original moisture content, preserving viability until sowing (Sumita and Simanta, 2018). This approach enhances seed performance under both optimal and stress conditions by synchronizing germination, improving emergence uniformity and strengthening seedling vigor (de Oliveira and Gomes-Filho, 2016).
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