Field Crop 2024, Vol.7, No.3, 134-144 http://cropscipublisher.com/index.php/fc 135 2 Overview of Seedling Diseases in Cotton 2.1 Common seedling diseases Cotton seedlings are susceptible to a variety of diseases that can significantly impact crop establishment and yield. Among the most prevalent seedling diseases are preemergence damping-off, postemergence damping-off, and various wilt diseases. Preemergence damping-off, often caused by pathogens such as Pythium spp. and Rhizopus oryzae, leads to seed decay and failure to emerge (Howell, 2002). Postemergence damping-off, caused by fungi like Pythium spp., Rhizoctonia solani, and Fusarium spp., results in seedling death shortly after emergence (Parkash et al., 2021). Wilt diseases, including Verticillium wilt and Fusarium wilt, are also common and can cause severe damage to cotton seedlings, leading to stunted growth and reduced yield (Halpern et al., 2017; Yuan et al., 2017). 2.2 Pathogens involved Several pathogens are responsible for seedling diseases in cotton. Pythiumspp., including P. aphanidermatumand P. ultimum, are major contributors to preemergence damping-off (Howell, 2002). Rhizopus oryzae is another significant pathogen causing preemergence damping-off (Howell, 2002). Postemergence damping-off is primarily caused by Pythiumspp., Rhizoctonia solani, and Fusariumspp. (Halpern et al., 2017). Verticillium dahliae is the pathogen responsible for Verticillium wilt, a disease that severely limits cotton production (Yuan et al., 2017). Fusarium oxysporum f. sp. vasinfectum, particularly race, is a highly virulent pathogen causing Fusarium wilt, which can lead to severe early-season damage (Parkash et al., 2021). Additionally, Bacillus strains have been identified as pathogenic to cotton seedlings, causing damping-off and affecting seedling growth (Aly et al., 2022). 2.3 Symptoms and diagnosis The symptoms of seedling diseases in cotton vary depending on the pathogen involved. Preemergence damping-off is characterized by seed decay and failure to emerge from the soil. Postemergence damping-off symptoms include seedling death shortly after emergence, with affected seedlings showing signs of rot at the soil line. Verticillium wilt symptoms include wilting, chlorosis, and necrosis of leaves, as well as vascular discoloration in stems. Fusariumwilt symptoms are similar, with wilting, root rot, and stem discoloration being common indicators. Diagnosis of these diseases typically involves isolating and identifying the pathogens from infected plant tissues or soil samples. For instance, Pythium spp. and Rhizoctonia solani can be isolated from discolored or necrotic hypocotyls of cotton seedlings. Advanced diagnostic techniques, such as molecular assays, can also be used to accurately identify specific pathogens like V. dahliae and F. oxysporum. By understanding the common seedling diseases, the pathogens involved, and their symptoms, effective management strategies can be developed to mitigate the impact of these diseases on cotton crop establishment and yield. 3 Factors Contributing to Seedling Diseases 3.1 Environmental conditions Environmental conditions play a significant role in the prevalence and severity of seedling diseases in cotton crops. Variations in soil temperature and moisture content have been shown to affect the incidence of seedling blight, with certain fungi thriving under specific conditions. For instance, Pythium spp. were most prevalent in cooler temperatures, while Fusariumspp., Rhizoctonia solani, and Thielaviopsis basicola were more common in warmer months (Hayat et al., 2020). Additionally, climate change and its associated weather patterns, such as extreme temperatures and altered rainfall, can exacerbate the occurrence of diseases by creating favorable conditions for pathogens and pests (Bhatti et al., 2020). 3.2 Soil health and composition Soil health and composition are key factors influencing the development of seedling diseases. The presence of specific soil pathogens, such as Pythium spp., Fusarium spp., Rhizoctonia solani and Thielaviopsis basicola, is related to soil type and its crops Planting history. For example, soils that have not been planted with cotton have higher incidences of Pythiumand Fusariumspecies, while soils with a history of cotton cultivation have higher incidences of Rhizoctonia solani and Rhizopus black rot (Hayat et al., 2020). In addition, soil characteristics such as pH, electrical conductivity, organic matter content, and the presence of trace elements such as zinc, copper, and
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