International Journal of Horticulture, 2025, Vol.15, No.5, 242-256 http://hortherbpublisher.com/index.php/ijh 243 antioxidant activity and maintaining membrane stability under heat stress conditions (Khan et al., 2023). Biopriming has also gained attention for its dual role in stress mitigation and the promotion of nutrient acquisition and plant defense mechanisms (Rajendra Prasad et al., 2016). Despite these advancements, most studies have addressed single-stress conditions under controlled environments. There is a critical knowledge gap in understanding how seed priming may mediate cross-tolerance, the capacity of plants to tolerate multiple concurrent stresses after exposure to a single stimulus (Ramegowda et al., 2020). This is of particular importance given that climate-induced stressors often occur in combination (e.g., drought with high temperature or salinity), presenting more complex physiological challenges than individual stresses. Additionally, the lack of standardized protocols for priming treatments and the limited availability of multi-environment field trials hinders the broader application of these techniques in horticultural production systems. Therefore, this review aims to comprehensively assess the current state of knowledge on seed priming in horticultural crops, with a special focus on its role in promoting multi-stress resilience. It synthesizes the physiological, biochemical and molecular mechanisms activated by different priming agents, evaluates the potential for cross-tolerance and highlights key research gaps, particularly regarding priming under combined stress scenarios and its scalability to field-level applications. Addressing these gaps is essential to optimize seed priming strategies for real-world use and to enhance the sustainability of horticultural production under climate variability. 2 Key abiotic Stresses and Their Impacts on Horticultural Crops Horticultural crops are particularly sensitive to abiotic stress due to their delicate physiology, shallow root systems, and high-water content. The most common abiotic stressors include drought, salinity and extreme temperatures (both heat and cold). These factors disrupt physiological processes at multiple stages of development, from germination to postharvest, resulting in significant economic and agronomic losses and their impacts are often magnified when they occur in combination (Rao et al., 2016; Francini and Sebastiani, 2019). 2.1 Drought stress Drought is one of the most widespread and damaging abiotic stresses affecting agricultural production worldwide (Borgohain et al., 2019). This challenge undermines the sustainability of agricultural systems and is further intensified by the rising global demand for food, driven by the steady growth of the world population (Seleiman et al., 2021). It induces osmotic stress, leading to stomatal closure and reduced leaf expansion, which collectively impair the plant's ability to perform gas exchange and transpiration (Salehi-Lisar and Bakhshayeshan-Agdam, 2016; Fahad et al., 2017). Consequently, photosynthetic rates decline due to alterations in chlorophyll content and disruptions in enzyme activity (Reddy et al., 2004). Additionally, drought stress disrupts hormonal balance, particularly by increasing abscisic acid (ABA) synthesis, which further reinforces stomatal closure and inhibits cell elongation (Souza and Cardoso, 2003). In crops like tomato (Solanum lycopersicum L.) and pepper (Capsicum annuum L.), prolonged water stress is also associated with increased susceptibility to blossom-end rot due to reduced calcium mobility within the plant (Saure, 2014). At the metabolic level, drought stress often triggers the accumulation of osmoprotectants (e.g., proline, trehalose) and the upregulation of antioxidant enzymes like superoxide dismutase (SOD) and catalase (CAT) as defensive responses (Rejeb et al., 2014). 2.2 Salinity stress Soil salinization is among the most critical abiotic constraints limiting agricultural productivity on a global scale. It may occur naturally (referred to as primary salinization) or arise from anthropogenic activities, particularly poor irrigation management, known as secondary salinization (Paz et al., 2023). Currently, salinity affects approximately 20% of the world’s irrigated land (around 45 million hectares) posing a substantial threat to crop yields in areas responsible for nearly one-third of global food production (Machado and Serralheiro, 2017).
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