Recent Advancements in Biotic and Abiotic Stress Responses and Regulation Mechanism in Horticultural Plants

1. Introduction

Horticultural plants are vital for global food security, providing essential nutrients, vitamins, and antioxidants that contribute to human health and well-being. However, these plants are increasingly subjected to various biotic and abiotic stresses, which threaten their growth, yield, and quality. Biotic stresses, such as pests, pathogens, and invasive species, along with abiotic stresses like drought, salinity, extreme temperatures, and climate change, pose significant challenges to horticultural production. Understanding the mechanisms by which plants respond to these stresses and developing strategies to enhance their resilience are crucial for achieving sustainable agriculture. This Special Issue of Horticulturae focuses on recent advancements in the responses and regulation mechanisms of horticultural plants to biotic and abiotic stresses.

2. Biotic Stress Responses

Biotic stresses, caused by pests and pathogens, are a major concern for horticultural production. The oriental fruit fly (Bactrocera dorsalis), for instance, is a highly destructive pest that infests a wide range of fruits and vegetables, leading to significant economic losses. Jaffar et al. [1] provide a comprehensive review of the invasion history, ecological adaptations, and management strategies of B. dorsalis in China. They also discuss various control methods, including quarantine measures, biological controls, and advanced genetic techniques such as RNA interference (RNAi) and CRISPR-Cas9, highlighting the importance of integrated pest management strategies. Additionally, aphids (Aphidoidea), whiteflies (Bemisia tabaci), and spider mites (Tetranychus urticae) are also common pests that affect a wide range of horticultural crops, causing significant damage to agricultural productivity [2]. Similarly, root-knot nematodes (Meloidogyne spp.) are notorious for their ability to infest plant roots, leading to severe crop losses [3]. Vashisth et al. [4] discuss the challenges posed by these nematodes and review various management strategies. These include crop rotation, resistant plant varieties, and biological controls such as nematophagous fungi. They also highlight the potential of genetic engineering and RNAi technology in developing nematode-resistant crops, underscoring the importance of a multi-faceted approach to pest management. Msabila et al. (contribution 1) demonstrate that grafting tomato cv. ‘Tanya’ onto resistant rootstocks like ‘EG203’ and ‘Hawaii 7796’ significantly reduces bacterial wilt incidence by up to 51% and improves yields by up to 57% in Tanzania, with combined water deficit further enhancing resilience. Huang et al. (contribution 2) comprehensively identify and analyze 91 reactive oxygen species (ROS) metabolism-associated genes in Citrus sinensis, revealing their roles in pathogen response, evolutionary conservation, and differential expression patterns during infections by Candidatus Liberibacter asiaticus and Xanthomonas citri. In addition to pest management, understanding the interactions between plants and pathogens is essential for developing resistant cultivars. Recent studies have explored the role of plant immune responses, including the activation of defense-related genes and the production of secondary metabolites, in combating pathogen attacks [5]. These findings are crucial for breeding programs aimed at enhancing disease resistance in horticultural crops.

3. Abiotic Stress Responses

Abiotic stresses, particularly those related to climate change, are becoming increasingly severe, affecting horticultural production worldwide. Drought, salinity, and extreme temperatures are among the most critical factors limiting plant growth and productivity. Recent research has focused on identifying key genes and pathways involved in abiotic stress responses, as well as developing biotechnological tools to improve stress tolerance. For example, studies on grapevines have shown that rootstock selection and training systems can significantly influence plant resilience to abiotic stresses [6]. Similarly, research on citrus crops has highlighted the importance of scion–rootstock compatibility in improving stress tolerance and fruit quality [7]. Climate change is a pressing issue that affects all aspects of horticultural production. Rising temperatures, altered precipitation patterns, and increased frequency of extreme weather events are expected to exacerbate both biotic and abiotic stresses. Zhang et al. [8] review the molecular mechanisms underlying the responses of plants to abiotic stresses and emphasize that multiple processes are involved, including sensing, signaling, transcription, transcript processing, and translation and post-translational proteFigurein modifications. Li et al. (contribution 3) identify AmCHIA as a key protein enhancing cold tolerance in Ammopiptanthus mongolicus through proteomic analysis, revealing its role in stress adaptation and potential applications in genetic engineering for cold-resistant crops. Shang et al. (contribution 4) report that RhMED15a regulates drought tolerance in roses by modulating stress-responsive genes and hormone signaling, with silencing experiments confirming its critical role in improving plant survival under water-deficient conditions. Baldi et al. (contribution 5) indicates that a transcriptomic analysis of kiwifruit under drought and waterlogging stresses highlights distinct molecular responses, including altered hormone signaling and secondary metabolism, with drought having a more pronounced impact on gene expression than waterlogging. Zhou et al. [9] demonstrate that the soybean transcription factor GmMYB84, induced by salinity stress through DNA demethylation of its promoter, enhances salt tolerance by regulating ion homeostasis (via GmAKT1), improving antioxidant activity, and increasing proline accumulation, thereby promoting germination and root growth in both soybean and Arabidopsis. Lu et al. (contribution 6) found that strigolactones (SLs) enhance salt tolerance in tomato seedlings by modulating trehalose (Tre) metabolism—upregulating Tre biosynthesis genes (TPS1, TPS2, TPP1, TPP2) and enzymes (TPS, TPP) while suppressing Tre degradation (THL activity)—thereby increasing Tre accumulation and mitigating salt-induced growth inhibition. These findings underscore the need for adaptive strategies, such as selecting heat-tolerant cultivars and modifying vineyard management practices, to mitigate the effects of climate change.

4. Sustainable Practices and Future Directions

Sustainable agricultural practices are essential for ensuring the long-term viability of horticultural production. Intercropping, for example, has been shown to improve resource use efficiency, enhance soil health, and reduce pest and disease incidence. Lv et al. [10] found that intercropping faba bean with wheat significantly suppressed Fusarium wilt by reducing pathogen-stimulated root exudates (phenolic acids, organic acids, amino acids, and sugars), thereby limiting Fusarium oxysporum f. sp. fabae proliferation and enhancing disease resistance through altered rhizosphere dynamics.

As the horticultural industry faces increasing challenges from biotic and abiotic stresses, ongoing research and innovation are critical. Advances in genomics, biotechnology, and precision agriculture offer promising tools for developing stress-tolerant cultivars and optimizing crop management practices. However, the successful implementation of these technologies requires a multidisciplinary approach, involving collaboration among researchers, growers, and policymakers.

5. Conclusions

This Special Issue provides a comprehensive overview of recent advancements in understanding and managing biotic and abiotic stress responses in horticultural plants. The articles contributed highlight the importance of integrating physiological, biochemical, and molecular insights with innovative agricultural practices to enhance plant resilience and ensure sustainable production. As the global climate continues to change, ongoing research and adaptive strategies will be essential for safeguarding the future of horticultural crops and the livelihoods of those who depend on them.