Molecular Pathogens, 2025, Vol.16, No.2, 45-52 http://microbescipublisher.com/index.php/mp 46 disease-resistant genes into species that are prone to infection and improve the persistence of disease-resistant ability (Ashkani et al., 2015; Sahu et al., 2022). 146 disease-resistant genes for rice blast have been found, of which 37 have been studied in detail. These studies lay the foundation for us to develop disease-resistant varieties using marker breeding and gene editing techniques. There are also some genetically modified methods, such as adding the chitinase 1 gene of corn to rice, which also shows certain disease resistance (Anwaar et al., 2024). 2.2 Sheath blight (Rhizoctonia solani): challenges and resistant varieties Trefoil blight is caused by a pathogen called Rhizoma delta and is also harmful to rice. However, no genes that are completely resistant to diseases have been found, which makes breeding difficult. Environmental factors can also easily aggravate the condition, such as when the temperature is high and the humidity is high, the disease will be even more serious. Nowadays, breeding work mainly relies on finding varieties with "partial resistance", but this resistance will also be affected by the environment. The good news is that with the development of molecular genetics, researchers have found a lot of QTLs related to anti-treatment blight. These findings allow us to slowly breed rice with stronger disease resistance using marker-assisted selection methods (Zarbafi and Ham, 2019). However, these resistances are not stable enough and further research and improvement are needed. 2.3 Brown spot (Bipolaris oryzae) and genetic sources of resistance Brown spot disease is also a fungal disease, which has become more common in recent years due to rising temperatures. The bacteria of this disease grow especially fast at high temperatures, so warming makes it easier to explode. Compared with other rice diseases, no complete disease-resistant gene has been found in brown spot disease. Therefore, everyone can only rely on some resistance strategies. Through research, scientists have discovered some QTLs related to anti-brown spot disease, which is very important for breeding efforts (Mizobuchi et al., 2016). Only by constantly screening resistant materials and adding molecular breeding methods can this disease be better controlled and provide guarantees for the continuous production of rice. 3 Bacterial Diseases and Breeding for Resistance 3.1 Bacterial leaf blight (Xanthomonas oryzae pv. oryzae) 3.1.1 Major resistance genes (Xa genes) and their role Rice white leaf blight (BLB for short) is a very serious problem in rice cultivation and is caused by the white leaf blight bacteria (Xoo). It is currently found that whether rice can resist this disease is mainly related to a disease-resistant gene called “Xa gene”. These genes are very important for cultivating disease-resistant rice varieties. So far, scientists have found 44 Xa genes, 15 of which have been successfully cloned and studied (Joshi et al., 2020; Yang et al., 2022). These genes can recognize the substances released by the bacteria and then activate the rice’s own defense response, so they play a key role in preventing diseases. 3.1.2 Development of Xa-gene-pyramided varieties The researchers found that putting several different Xa genes into the same rice variety can make the disease resistant stronger. This practice is called “gene stacking” or “gene pyramid”. For example, some modified varieties such as Pusa Basmati-1 and Samba Mahsuri have introduced gene combinations such as xa5, Xa4, xa13 and Xa21, and the ability to resist BLB has been significantly improved. In this process, scientists used marker-assisted selection techniques, which can more conveniently integrate multiple disease-resistant genes into one variety (Huang et al., 2023; Yang, 2024). This also makes breeding faster and more accurate. 3.1.3 Field trials and resistance stability Doing field experiments is a very important step. It can help us understand whether these varieties with multiple Xa genes can really resist diseases in different places and climates. These tests allow us to determine whether these disease-resistant varieties are effective for different types of Xoo strains. If the disease resistance can play a stable role in the long term, it means that this variety is successful and is more suitable for promotion and cultivation. Therefore, field tests are essential to verify the resistance effect.
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