Molecular Pathogens, 2025, Vol.16, No.4, 171-181 http://microbescipublisher.com/index.php/mp 176 5 Global and Regional Disease-Resistant Varieties Research and Development Results 5.1 Disease-resistant breeding results in major rice crop areas in Asia Asia is the central area for rice cultivation and production, and is also one of the areas where bacterial diseases of rice occur most frequently. In the long-term struggle against diseases, breeders from Asian countries have accumulated rich experience in the research and development of disease-resistant varieties and achieved remarkable results. In the 1980s, China used the Xa21 gene cloned from African wild rice to cultivate a series of anti-white leaf blight strains, and introduced Xa21 into hybrid rice parents, and bred it into disease-resistant combinations such as the Xieqingzao series, which played a huge role in production. In Japan, in the 1970s, local varieties that are resistant to white leaf blight were screened, and genetic factors such as Xa1 were identified, and they were introduced into excellent japonica varieties, and disease-resistant varieties such as moonlight were bred. The epidemic of white leaf blight was effectively controlled in southwestern Japan. South and Southeast Asian countries have become more common due to the prevalence of white leaf blight, and the investment in disease-resistant breeding is also the largest. The Philippine International Rice Research Institute (IRRI) established a global rice disease resistance screening system as early as the 1970s and collected a large number of source-resistant materials for hybrid breeding. The famous IR series varieties such as IR20 and IR24 carry a certain degree of resistance. IRRI further aggregates different resistance genes through incross backbreeding, and develops a series of near isogenic lines (IRBB lines), specifically used to provide disease-resistant genes (Tu et al., 2000). In recent years, India has cultivated several broad-spectrum anti-white leaf blight varieties through national research and development plans, such as Improved Samba Mahsuri (introduced Xa21, xa13, etc.) and has achieved success in production (Sakthivel et al., 2017). 5.2 Progress in disease-resistant breeding in Africa and America Compared with Asia, the problem of bacterial disease in rice in Africa and the Americas has not been prominent in the past. Some countries in western Africa (such as Senegal, etc.) have reported the occurrence of bacterial strabular plaque in rice in recent years, suggesting that the disease may become an emerging threat in Africa. To this end, the African Rice Research Center has begun to lay out related disease-resistant breeding research. On the one hand, they introduced and evaluated disease-resistant germplasms from Asia, including the multi-resistant gene-carrying strains provided by IRRI and the hybrid rice germplasm provided by China, hoping to introduce important resistance genes into native African adaptive varieties. On the other hand, resistance screening was conducted for native African rice seeds (such as O. glaberrima, etc.), and some gene sources that are resistant to white leaf blight were also found. In the Americas, the major rice-producing countries in South America, such as Brazil and Colombia, have also been attacked by white leaf blight in history. In the 1980s, a white leaf blight outbreak occurred in Brazil. For this reason, research institutions such as Embrapa introduced disease-resistant materials from Japan to breed and cultivated a number of disease-resistant strains. Some varieties carrying genes such as Xa4 have effectively controlled the prevalence of diseases after being promoted in South America (Sabar et al., 2016). Currently, rice varieties in Latin America have more or less integrated one or two major anti-white leaf blight genes. For example, the Fedearroz series of Colombia usually has Xa21 or Xa4 background, so that white leaf blight rarely occurs in production and is widely prevalent. Sporadic strains of straber plaque have been monitored in rice fields in southern United States in recent years, indicating that the pathogen may be introduced through seed trade. 5.3 International cooperation and germplasm sharing Progress in rice disease-resistance breeding depends on international cooperation and the sharing of germplasm resources. International trials led by the International Rice Research Institute (IRRI), such as the International Blast Nursery and the International Bacterial Blight Nursery, allow breeders from various countries to evaluate the resistance of their varieties on a unified platform and to obtain disease-resistant materials from other sources. International cooperation is also underway in antibacterial strabular disease. Since the disease was mainly limited to tropical Asia in the past, researchers outside some regions paid less attention to it. But as climate warms and the spread of the disease, the rest of the world has also begun to value the disease and seek resistance resources. China
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