Field Crop 2024, Vol.7, No.4, 212-221 http://cropscipublisher.com/index.php/fc 215 Zhu et al. (2023) illustrates the infection cycle of Verticillium dahliae in host plants, highlighting its stages from root exudate detection to systemic colonization and eventual formation of microsclerotia. The infection begins when microsclerotia in the soil germinate upon sensing signals from root exudates, allowing the fungus to penetrate the roots and colonize the xylem. V. dahliae progresses through biotrophic and necrotrophic stages, causing wilting, chlorosis, and ultimately death of the host. The necrotrophic stage leads to the formation of new microsclerotia, ensuring long-term survival. The study also notes that environmental factors and host plant conditions significantly influence the incidence and severity of Verticillium wilt, underscoring the disease's complexity and impact on cotton and other crops. 3.2 Disease symptoms and their effect on plant physiology The symptoms of cotton diseases vary but generally include wilting, chlorosis, necrosis, and defoliation, which severely affect plant physiology and fiber quality. Verticilliumwilt manifests as wilting and chlorosis of leaves, vascular discoloration, and stunted growth, ultimately leading to significant yield losses and reduced fiber quality (Zhu et al., 2023). Fusariumwilt symptoms include yellowing and wilting of leaves, vascular browning, and plant death, which also result in substantial yield and quality reductions (Bardak et al., 2021). Powdery mildew caused by Brasiliomyces malachrae presents as white mycelial patches on leaves, leading to yellowing, necrosis, and early defoliation, which can compromise the photosynthetic efficiency and overall health of the cotton plant (Márquez-Licona et al., 2023). These symptoms disrupt normal physiological processes such as photosynthesis, nutrient transport, and water uptake, thereby impairing fiber development and quality (Ul-Allah et al., 2021). 3.3 Factors influencing disease severity Several factors influence the severity of cotton diseases, including environmental conditions, genetic resistance, and pathogen virulence. Environmental stresses such as drought and salinity can exacerbate disease severity by weakening the plant's defense mechanisms and making it more susceptible to infections (Tahmasebi et al., 2019; Billah et al., 2021). Genetic resistance plays a crucial role in disease management; however, the limited availability of resistance genes in current cotton varieties poses a challenge for breeding programs (Zhang et al., 2020; Zhu et al., 2023). The virulence of the pathogen, including its ability to produce toxins and secondary metabolites, also significantly impacts disease severity. For instance, the ubiquitin ligase VdBre1 in V. dahliae regulates lipid metabolism and secondary metabolite production, which are critical for the pathogen's virulence and ability to infect cotton (Wang et al., 2020). Additionally, the presence of specific genetic markers associated with disease resistance can aid in the development of resistant cotton varieties through marker-assisted selection (MAS) (Bardak et al., 2021). By understanding these pathogen mechanisms and disease progression, researchers can develop more effective strategies to mitigate the impact of cotton diseases on fiber quality and production. 4 Impact on Fiber Quality and Production 4.1 Effects on fiber length and strength Cotton diseases significantly impact fiber length and strength, which are critical parameters for textile quality. Verticilliumwilt, caused by Verticillium dahliae, has been shown to reduce fiber quality, including fiber length and strength. In a study comparing healthy and Verticillium wilt-affected plants, fiber properties such as short fiber content and nep count were significantly affected, indicating a reduction in fiber length and strength under disease pressure (Ayele et al., 2020). Additionally, genomic studies have identified specific loci associated with fiber length and strength, providing targets for genetic improvement to mitigate these effects (Ma et al., 2018). The comparative analysis of Gossypium hirsutum and Gossypium barbadense genomes also highlights the genetic basis for differences in fiber quality, with G. barbadense producing superior-quality fibers (Hu et al., 2019). 4.2 Impact on fiber maturity and uniformity Fiber maturity and uniformity are crucial for processing efficiency and final product quality. Verticilliumwilt has been shown to decrease the maturity ratio of cotton fibers, with significant reductions observed in susceptible genotypes (Ayele et al., 2020). The symbiosis with arbuscular mycorrhizal fungi (AMF) has been reported to enhance fiber maturity, suggesting a potential biological control strategy to improve fiber quality under disease
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