Field Crop 2024, Vol.7, No.6, 287-297 http://cropscipublisher.com/index.php/fc 293 since spread to major kiwifruit-growing regions, including Korea, Italy, and New Zealand. The pathogen is genetically diverse, with strains grouped into four biovars based on molecular and pathogenic characteristics. The recent outbreaks, particularly those caused by biovar 3, have been highly virulent, affecting over 60% of the kiwifruit plantations in New Zealand within two years (Reglinski et al., 2013). 6.2 Molecular and genetic basis of resistance The molecular mechanisms underlying kiwifruit resistance to Psa involve complex interactions between the plant's defense pathways and the pathogen. Salicylic acid (SA) has been identified as a key regulator in enhancing kiwifruit's resistance to Psa. SA treatment induces significant changes in the proteomic patterns of kiwifruit, activating resistance pathways such as the MAPK cascade, phenylpropanoid biosynthesis, and hormone signaling transduction (Qu et al., 2023). Additionally, sulfur treatments have been shown to increase the activities of defense-related enzymes like phenylalanine ammonia-lyase (PAL), peroxidase (POD), and polyphenol oxidase (PPO), and promote lignin accumulation, which strengthens the plant's structural defenses (Gu et al., 2021). 6.3 Breeding approaches and biotechnological interventions Breeding for resistance to bacterial canker in kiwifruit involves both traditional and biotechnological approaches. One effective strategy has been the use of acibenzolar-S-methyl (ASM), a commercial elicitor of host resistance, which has shown promising results in enhancing resistance in both Actinidia chinensis and A.deliciosa (Reglinski et al., 2013). Furthermore, sulfur treatments have demonstrated high protection efficiency, reducing disease severity and improving the morphological defenses of kiwifruit stems (Gu et al., 2021). These findings suggest that integrating chemical elicitors and sulfur treatments into breeding programs could enhance the development of resistant kiwifruit varieties. 6.4 Future directions and challenges Future research should focus on elucidating the detailed molecular mechanisms by which SA and sulfur induce resistance in kiwifruit. Understanding the specific genes and pathways involved could lead to the development of more targeted and effective breeding strategies. Additionally, there is a need to explore the potential of combining multiple resistance-inducing treatments to achieve synergistic effects. The challenge remains in translating these findings into practical, sustainable solutions that can be widely adopted by the kiwifruit industry. Continuous monitoring and management of pathogen diversity and virulence are also crucial to stay ahead of evolving threats. By integrating molecular insights with practical breeding and biotechnological interventions, the kiwifruit industry can develop robust strategies to combat bacterial canker and ensure sustainable production (Li et al., 2023). 7 Integrative Approaches to Enhancing Kiwifruit Stress Resistance 7.1 Combined physiological, biochemical, and molecular strategies Kiwifruit's resistance to environmental stress can be significantly enhanced through a combination of physiological, biochemical, and molecular strategies. For instance, the bZIP transcription factor AcePosF21 has been identified as a key player in the biosynthesis of ascorbic acid (AsA) during cold stress. This factor interacts with the R2R3-MYB transcription factor AceMYB102 to upregulate the expression of GDP-L-galactose phosphorylase 3 (AceGGP3), thereby increasing AsA production and reducing oxidative damage caused by reactive oxygen species (ROS) (Liu et al., 2023). Additionally, the R1R2R3-MYB transcription factor AcMYB3R has been shown to enhance drought and salinity tolerance in Arabidopsis thaliana by upregulating stress-responsive genes such as RD29A, RD29B, COR15A, and RD22 (Zhang et al., 2019). These findings underscore the importance of transcription factors in modulating stress responses at the molecular level. 7.2 Role of biotechnology and genetic engineering Biotechnology and genetic engineering offer promising avenues for enhancing kiwifruit's resistance to various stresses. The use of virus-induced gene silencing (VIGS) and overexpression techniques has revealed that miR160d positively regulates kiwifruit resistance to Botrytis cinerea by increasing antioxidant enzyme activities and the content of phytohormones like indole-3-acetic acid (IAA) and salicylic acid (SA) (Li et al., 2023). Furthermore, grafting kiwifruit onto waterlogging-tolerant rootstocks such as KR5 has been shown to improve
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