Plant Responses to Biotic and Abiotic Stresses: From Cellular to Morphological Changes—Series II

Plants continually encounter biotic and abiotic stresses, which threaten their growth, development, and productivity. Biotic stresses emanate from interactions with other living organisms, such as pathogens, pests, and weeds, whereas abiotic stresses result from environmental factors, such as drought, salinity, extreme temperatures, and heavy metal toxicity, among many others [1,2]. In response, plants have developed elaborative mechanisms of survival and adaptation at the cellular, molecular, and morphological levels. These mechanisms include signal perception and transduction, the activation of stress-responsive genes, and physiological changes that confer resilience or resistance. Key examples include the accumulation of osmoprotectants, reactive oxygen species-scavenging enzymes, and stress-responsive hormones like abscisic acid under abiotic stresses, which play a crucial role in damage mitigation [3]. Conversely, biotic stress responses include the recognition of pathogen-associated molecular patterns, the activation of defense pathways such as SAR, and the hypersensitive response [4]. Additional morphological changes, including root architectural alterations, leaf area, and stomatal dynamics, further enhance resilience by optimizing resource allocation under stressful conditions. Understanding the interplay of these responses, from cellular signaling cascades to whole-plant adaptations, provides valuable insights into plant resilience. This understanding offers avenues for developing stress-tolerant crop varieties, ensuring agricultural sustainability in the context of global climate change [5,6].

Abiotic stresses, such as drought, heat, cold, and heavy metal contamination, remain significant constraints on global crop productivity [7]. Gaining a comprehensive understanding of physiological and molecular plant responses to these stresses is critical for developing resilient crop varieties. Alghabari et al. [8] explored the resilience of synthetic hexaploid wheat germplasm under the combined effects of drought and heat stress, two interrelated challenges expected to intensify with climate change. The study utilized a comprehensive set of physiological, biochemical, and agronomic traits to evaluate wheat performance, revealing significant genotypic variability among the tested germplasm. These findings highlight the potential of synthetic wheat in breeding programs designed to enhance stress tolerance by identifying superior genotypes. Furthermore, the research underscores the critical importance of multi-trait evaluations in breeding strategies, as single-trait approaches often fail to capture the multifaceted nature of plant responses to abiotic stress.

Zhang et al. [9] tackled the impact of late-spring cold weather (LSCW) on wheat, a significant challenge that disrupts growth and reduces yield. Their field and pot trials across different wheat varieties revealed key anatomical and physiological adaptations associated with cold tolerance. These findings provide valuable markers for breeders to select cold-resistant wheat varieties, enhancing crop resilience to increasingly unpredictable weather patterns. Similarly, Wen et al. [10] examined cold tolerance in broccoli seedlings, identifying robust cultivars such as Meiqing and King 11. Their methodological framework for evaluating cold tolerance offers a replicable model for similar studies in other crops, contributing to the broader development of climate-resilient agriculture. Furthermore, Deng et al. [11] focused on cadmium (Cd) stress in maize, a critical issue in regions with high soil contamination. Their study revealed significant genotypic differences in maize responses to Cd exposure, providing actionable insights for breeding programs aimed at improving food safety and environmental sustainability. This research highlights the urgency of addressing heavy metal contamination, which is a growing concern in intensively farmed and polluted industrial areas.

Biotic stresses, caused by fungi, bacteria, viruses, and pests, remain significant threats to crop productivity [12]. Effective management strategies require accurate identification, an understanding of pathogen–host interactions, and the implementation of targeted control measures.

Goura et al. [13] conducted a comprehensive study of fungal pathogens causing trunk and branch cankers in almond trees in Morocco, as these are an economically and culturally important crop in the region. Through pathogen isolation, DNA sequencing, and pathogenicity assays, they identified species such as Curvularia hawaiiensis, Fusarium ambrosium, Lasiodiplodia theobromae, and Chondrestereum purpureum. Among these, Lasiodiplodia theobromae emerged as the most virulent, highlighting its potential as a major threat to almond orchards. Importantly, some of these fungal species were reported for the first time in Morocco and, in certain cases, globally, in almond trees. This research expands our knowledge of fungal pathogens in almonds and establishes a foundation for the development of integrated disease management strategies that could benefit almond-growers in Morocco and similar agroecosystems worldwide. The findings emphasize the need for the continuous monitoring of pathogens, and the development of region-specific diagnostic tools and biosecurity protocols. Future work could focus on integrating genomic tools with remote sensing technologies for rapid pathogen detection and real-time monitoring in orchards.

At the molecular level, plants deploy intricate networks to perceive, respond to, and mitigate stress impacts. Movahedi et al. [14] provided a thorough review of drought-responsive protein pathways, with a particular emphasis on abscisic acid signaling, the roles of dehydrins, and pathway crosstalk. Their synthesis of the existing research offers a roadmap for leveraging protein pathways to engineer drought tolerance in crops, while also identifying opportunities for integrating protein pathway data with genome editing technologies like CRISPR.

The path forward lies in embracing interdisciplinary research and collaboration across sectors. Advances in genomics, proteomics, and bioinformatics will be essential for identifying stress-tolerant genes and pathways [15]. In parallel, precision agriculture tools, including remote sensing and machine learning, can enhance the monitoring and management of stress responses in real-time [16]. Breeding programs should focus on developing varieties that are resilient to multiple stressors, including combinations of biotic and abiotic challenges [17]. For instance, integrating drought-tolerant and pathogen-resistant traits into a single variety could significantly enhance agricultural resilience [18]. Additionally, there is a growing need for field-based validations of laboratory findings. The field-based validation of laboratory findings through long-term field trials in diverse agroecological settings is essential to refine stress management strategies and ensure their effectiveness under real-world conditions.

This Special Issue highlights the complexity of plant stress responses and the innovative strategies being developed to address them. By bridging the fundamental research with applied solutions, the studies contribute to a more resilient and sustainable agricultural system. As global challenges evolve, the integration of cutting-edge science, traditional knowledge, and practical applications will be vital for ensuring food security and environmental sustainability.