Molecular Microbiology Research, 2025, Vol.15, No.2, 69-81 http://microbescipublisher.com/index.php/mmr 73 Although MAS has achieved initial results in actual breeding, its reliability is still affected by the linkage stability between the marker and the target gene, especially when multi-disease resistance is aggregated, the risk of recombination is high. For this reason, the current breeding process is gradually introducing the whole genome selection (Genomic Selection, GS) model. GS integrates high-density whole-genome markers and phenotypic databases and uses predictive models to evaluate the resistance potential of offspring, thereby improving selection efficiency and accuracy in the early stages of breeding. Figure 1 The potential market of biopesticide 4.2 Gene editing and transgenic strategies 4.2.1 Application of CRISPR/Cas system in disease resistance improvement CRISPR/Cas gene editing technology provides a new tool for the precise improvement of cotton disease resistance traits (Chen et al., 2021). This technology can knock out susceptible genes in a targeted manner or activate key components of disease resistance pathways to give plants new resistance. Zhang et al. (2018) edited the Gh14-3-3d gene in cotton through CRISPR/Cas9 to downregulate its expression, thereby improving cotton's resistance to Verticilliumwilt. Experiments have shown that the mutant showed lighter lesions and lower disease index after inoculation with V. dahliae. In addition, researchers also used CRISPR technology to target and regulate genes related to plant resistance signaling pathways, such as NPR1, WRKY, MAPK, etc., to systematically enhance plant immunity (Ma et al., 2023). Since cotton is an allotetraploid crop with a complex genome, CRISPR's multi-site targeted editing and homologous copy recognition accuracy requirements are high. To improve editing efficiency, studies have introduced virus-mediated expression systems (such as TRV-mediated VIGE technology) to achieve transient and specific editing in cotton, improving the verification efficiency of disease-resistant candidate genes (Chen et al., 2021). 4.2.2 Analysis of the effect of the introduction of exogenous disease-resistant genes Traditional transgenic methods can also significantly improve cotton's resistance to fungal diseases by introducing disease-resistant genes from plants, animals or microorganisms. Gaspar et al. (2014) introduced tobacco NaD1 defensin into cotton, and the resulting transgenic strains showed good resistance to Verticilliumwilt and Fusarium wilt in both greenhouses and fields. These defensins have direct antibacterial activity and can kill bacteria by destroying the membrane structure of pathogens. In addition, antibacterial proteins such as HEWL (hen egg white lysozyme) have also been introduced into cotton, significantly improving immunity to pathogens such as Fusarium (Ramadan et al., 2020). In my country, a research team expressed chitosanase genes and peptide antifungal genes in cotton, enhancing the root's ability to protect against pathogen infection (Zhao et al., 2022).
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