Cotton Genomics and Genetics 2025, Vol.16, No.3, 137-147 http://cropscipublisher.com/index.php/cgg 138 using these molecular research results to breed disease-resistant cotton. In addition, we will also explore the future direction of achieving sustainable cotton disease control in the context of changing environments such as climate change. 2 Overview of Verticillium Wilt and Fusarium Wilt in Cotton 2.1 Pathogen characteristics and infection biology of Verticillium dahliae and Fusarium oxysporum Verticillium wilt is caused by a soil-dwelling fungus called Verticillium wilt. Fusarium wilt is caused by a specialized fungus called Vasinfectum (Abdelraheem et al., 2019). Both pathogens enter the cotton plant through the roots and eventually grow in the plant’s vascular tissue, interfering with the transport of water and nutrients. There are many different types of Verticillium wilt, some of which cause leaf drop and some do not, and they can survive in the soil for many years as microsclerotia (Wagner et al., 2020). Fusarium wilt also has many different types and multiple physiological subspecies. It also often occurs with root-knot nematodes, which can make the disease more severe. Both fungi are highly adaptable and can infect cotton from seedling to mature stage, which makes disease prevention and control very difficult. 2.2 Comparative symptoms and disease progression in cotton plants Both diseases cause cotton leaves to turn yellow, wilt, and in severe cases, necrosis, but their development process and symptoms are somewhat different. Verticillium wilt often causes leaves to turn yellow and lose water, with the lower leaves becoming infected first, and the vascular bundles turning brown. If infected with a deciduous strain, the plant will also lose leaves (Bhandari et al., 2020). Fusarium wilt often causes only one side of the leaves to turn yellow, the plant grows slower, and the vascular bundles change color. Sometimes the disease progresses to the death of the entire plant (Figure 1). If it occurs at the same time as nematodes, it will make the symptoms more severe. The severity and development speed of the disease are related to the virulence of the fungus itself, the number of infections, environmental conditions, and the disease resistance of the cotton variety. 2.3 Economic impact and geographical distribution of both diseases Verticillium wilt and Fusarium wilt are the two most damaging diseases to cotton worldwide, which can significantly reduce cotton yield and quality (Li et al., 2017b). In the United States, yield losses caused by Verticillium wilt ranged from 0.75% to 2.8% over the past 20 years. In China, Spain, and Uzbekistan, losses can reach 30% to 50%. Fusarium wilt has spread to all major cotton-producing areas and has recently been found in Australia. In 2001, it reduced average cotton yields in the United States by about 0.5%. The spread and severity of these two diseases are affected by the variety planted, crop rotation, and local climate. Long-term surveys in China have shown that these factors affect the occurrence of the disease. In major cotton-producing areas such as Xinjiang, China, these two pathogens often appear at the same time, making prevention and control more difficult and increasing the challenges of breeding disease-resistant varieties. 3 Cotton Innate Immune System and Defense Mechanisms 3.1 Pattern recognition receptors (PRRs) and PAMP-triggered immunity (PTI) Cotton detects fungi such as Verticillium dahliae and Fusarium oxysporum through pattern recognition receptors (PRRs) on the cell surface. These receptors recognize specific molecules carried by pathogens, also known as PAMPs (Liu et al., 2023). Once these molecules are recognized, cotton initiates PAMP-triggered immunity (PTI), which produces early defense responses. These responses include activation of MAPK cascade signaling pathways, production of reactive oxygen species (ROS), and initiation of expression of some defense-related genes (Zhou et al., 2020). For example, GauSR45a is a serine- and arginine-rich RNA-binding protein that regulates the alternative splicing of PTI-related immune genes (such as BAK1 and CERK1), thereby enhancing resistance to Verticillium wilt. In addition, somatic embryo receptor kinase (SERK) plays an auxiliary role in PTI signaling, which can interact with regulatory proteins such as GRF7 to further enhance cotton's immune response. 3.2 Effector-triggered immunity (ETI) and hypersensitive response When pathogens release effectors to interfere with PTI, cotton responds with a class of proteins inside the cell. These proteins are called NLRs, which are proteins containing nucleotide binding sites and leucine repeat
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