Rice Genomics and Genetics 2024, Vol.15, No.2, 69-79 http://cropscipublisher.com/index.php/rgg 70 marker-assisted breeding and the advantages of combining it with traditional breeding methods. In this challenging era, we believe that through in-depth research and informed decision-making, we can further improve rice's resistance to rice blast and make an important contribution to the global food supply and farmers' livelihoods. At the same time, we will explore future research directions to promote the development of more disease-resistant rice varieties to ensure global food security. 2 Research Progress on Rice Blast Disease 2.1 Overview of rice blast disease The pathogen of rice blast (Magnaporthe oryzae) is a fungus that is highly specialized and mainly infects rice plants, but can also cause similar diseases on other grass plants. The fungus overwinters on rice straw and rice with mycelium and conidia. When the temperature rises to about 20 °C the following year, a large number of conidia will be produced when rainfall occurs. Conidia are spread by air currents, raindrops, running water, and insects. In the presence of water and suitable temperature, appressoria germinate, produce hyphae, invade the host, and produce lesions. Under suitable temperature and humidity conditions, new conidia are produced, re-infected, and gradually expand and spread. The optimum temperature for mycelial growth is 25 °C to 28 °C; the optimum temperature for spore formation is 26°C to 28°C, and a relative humidity of more than 90% is required. Focus on areas with less sunshine, long duration of fog and dew, mountainous areas and areas along rivers and coastal areas with mild climate. Suitable temperature and high humidity are conducive to the onset of disease. Rice is most susceptible to the disease from the 4-leaf stage to the tillering stage and heading stage. When rice is in the susceptible stage, the temperature is between 20 °C and 30 °C, especially between 24 °C and 28 °C, there are many rainy days, and the relative humidity remains above 90%, which can easily cause serious occurrence of rice blast. Excessive, partial or late application of nitrogen fertilizer is conducive to bacterial infection; long-term deep irrigation or cold water irrigation will aggravate the disease (Ning et al., 2020). The life cycle of pathogenic bacteria includes multiple reproductive stages, the most important of which are conidia, ionic fruiting bodies and asexual spores. Conidia are the most common form of transmission of this pathogen, which are extremely small spores that are spread to rice leaves by wind. Asexual spores are another important form of transmission and are produced on infected tissues. It has a highly diverse genetics, and this diversity can develop through the evolution of different habitats and pathogenic bacterial strains, making it extremely adaptable. This is one of the reasons why this pathogen can cause disease in different geographical areas and rice varieties by producing special infection structures called "infectors" that penetrate the outer layer of rice leaves. Once inside the plant, it will infect different parts such as leaves, stems, and ears, leading to the spread of the disease. It has thousands of genes, some of which encode infection-related proteins, toxins and resistance genes. These genes play a key role in controlling the infection ability and resistance of pathogenic bacteria. The genome contains many genes encoding pathogenicity-related proteins that encode toxins, components of infection structures, and proteins involved in host interactions. Among them, pathogenicity-related proteins are key factors in infecting rice. Different expression patterns and combinations of pathogenic genes can affect the infectivity of pathogenic bacteria, allowing them to infect different rice varieties and resistant genotypes (Spence et al., 2014). The genetic diversity of pathogenic bacteria enables them to adapt to different rice varieties and environmental conditions, and there are extensive genetic differences between pathogenic bacteria strains, which is partly due to the high adaptability and evolutionary power of pathogenic bacteria. This diversity increases the complexity of the disease because different strains may produce different infectivity in resistant varieties, making it difficult to sustain resistance in resistant varieties. The control of rice blast mainly relies on disease-resistant rice varieties. Therefore, it is crucial to understand the pathogenic mechanism of pathogenic bacteria and the genetic basis of disease-resistant rice. By further studying
RkJQdWJsaXNoZXIy MjQ4ODYzNA==