Molecular Pathogens 2024, Vol.15, No.4, 200-208 http://microbescipublisher.com/index.php/mp 201 asexual spores: macroconidia, microconidia, and chlamydospores. Macroconidia are typically falcate and formed from phialides by basipetal division, while microconidia are ellipsoidal and also formed from phialides. Chlamydospores, on the other hand, are globose with thick walls and can form acrogenously from hyphae or by the modification of hyphal cells (Ohara et al., 2004; Ajmal et al., 2022). The taxonomy of Fusariumis complex, with many species exhibiting both sexual and asexual reproductive cycles, although fewer than 20% of Fusarium species have a known sexual cycle (Seong et al., 2008). 2.2 Infection process and disease development in cotton bolls The infection process of Fusarium spp. in cotton begins with the germination of spores on the plant surface, followed by the penetration of the fungal hyphae into the plant tissues. Fusarium oxysporum, a common pathogen in cotton, exhibits filamentous growth and produces spores that facilitate its spread and infection. The REN1 gene in F. oxysporum is essential for the development of microconidia and macroconidia, which are critical for the conidiation process and subsequent infection (Kurt et al., 2020). Once inside the plant, the fungus colonizes the vascular system, leading to the characteristic symptoms of Fusariumwilt, including yellowing, wilting, and boll rot. The disease development is further exacerbated by the production of mycotoxins, which can cause significant damage to the cotton bolls and reduce yield quality and quantity. 2.3 Environmental factors influencing pathogen growth and spread The growth and spread of Fusariumspp. are influenced by various environmental factors, including temperature, light, pH, host tissue, and nutrient availability. Optimal conditions for sporulation and infection vary among Fusarium species, but generally, warm and humid conditions favor the growth and spread of these pathogens. Temperature and light play significant roles in regulating the sporulation process, with specific ranges promoting the production of asexual spores (Moura et al., 2020). Additionally, the pH of the environment and the availability of nutrients can impact the growth rate and virulence of Fusariumspp. Understanding these environmental factors is crucial for developing effective control strategies to manage Fusariumdiseases in cotton, as manipulating these conditions can help inhibit the production and spread of spores, thereby reducing the incidence of boll rot. 3 Pathogen Dynamics in the Field 3.1 Transmission routes and sources of infection Fusarium oxysporumf. sp. vasinfectum(FOV), particularly race 4 (FOV4), is a soil-borne pathogen that poses a significant threat to cotton production. The primary transmission routes include soil and seed contamination. FOV4 can persist in the soil as chlamydospores and can be transmitted through infected seeds, which is a major concern for its spread across different regions (Cianchetta and Davis, 2015; Halpern et al., 2017). Additionally, insects such as stink bugs have been identified as vectors, capable of acquiring and transmitting FOV4 to cotton bolls, further complicating management efforts (Esquivel and Bell, 2021). The pathogen's ability to survive in the soil and its association with various hosts, including non-cotton plants, makes it a persistent threat in cotton fields (Zhang et al., 2021). 3.2 Host-pathogen interactions at different growth stages The interaction between FOV4 and cotton plants varies across different growth stages (Figure 1). At the seed germination stage, FOV4 can cause significant taproot rot, which is indicative of the plant's susceptibility to the pathogen. As the plant progresses to the seedling stage, symptoms such as wilting, root rot, and stem discoloration become more pronounced, leading to high seedling mortality rates (Zhang et al., 2021). The pathogen colonizes the vascular system of the plant, leading to systemic infection and severe disease symptoms (Chavez et al., 2022). Studies have shown that the disease severity rating (DSR) at early stages is significantly correlated with later stages, indicating that early infection can predict overall plant health and yield outcomes (Zhang et al., 2021; Zhu et al., 2023). 3.3 Effect of environmental conditions on disease severity Environmental conditions play a crucial role in the severity of Fusariumwilt in cotton. Temperature, soil moisture, and the presence of other soil microorganisms can influence the pathogen's activity and the plant's response. For
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