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This study aims to assess the distribution of cloned or mapped bacterial blight resistance genes (Xa1, Xa3, Xa4, xa5, Xa7, xa8, Xa10, xa13, Xa21, and Xa23) in newly developed and widely cultivated rice varieties in South China. It also evaluates the effectiveness of gene combinations in providing resistance. The findings provide a scientific basis for the rational deployment of bacterial blight-resistant rice genotypes and the application of these resistance genes in the region.
Using functional markers for the 10 resistance genes, 887 newly developed rice varieties from South China and 25 major rice varieties from Guangdong Province (2023-2024) were screened for resistance genes to bacterial blight. The resistance of 887 newly developed rice varieties to Xanthomonas oryzae pv. oryzae (Xoo) was identified by artificial leaf-cutting and inoculating with the dominant pathogenic strains of Xoo in South China. The resistance of the 25 major varieties in Guangdong Province was assessed using 102 representative strains from 11 major pathogenic types collected in 2024.
Of the 887 new rice varieties, the frequencies of varieties carrying Xa1, Xa23, Xa3, Xa7, Xa4, Xa21, and xa8 were 16.57%, 12.63%, 6.99%, 5.98%, 1.92%, 1.92%, and 0.34%, respectively, while no varieties carried xa5, Xa10, or xa13. Among the new varieties, 0.34% carried 4 resistance genes, 0.34% carried 3 genes, 6.99% carried 2 genes, 29.99% carried 1 gene, and 62.34% carried no resistance genes. Among the 68 new varieties with gene combinations, the most frequent genes were Xa23, Xa1, Xa3, Xa7, Xa4, and Xa21, with application frequencies of 63.23%, 63.23%, 38.23%, 27.94%, 14.71%, and 5.88%, respectively. Of the 887 varieties, 20.41% were resistant to the dominant Xoo pathogen in South China, while 79.59% were susceptible. The percentages of resistant varieties harboring only one of the genes Xa23, Xa4, xa8, Xa7, Xa21, Xa3, and Xa1 were 92.75%, 42.86%, 33.33%, 32.35%, 23.08%, 11.11%, and 7.69%, respectively. Among new varieties with 4, 3, 2, 1, and 0 resistance genes, the percentages of resistant varieties were 100%, 100%, 64.52%, 35.34%, and 7.41%, respectively. 65.22% of varieties with Xa23 were resistant or moderately resistant, and among the new varieties developed by pyramiding Xa23 with different genes, 79.07% were rated as resistant or above. Among the new varieties carrying Xa7, 61.76% showed moderate susceptibility or worse, and 90% of varieties with pyramided Xa7 and other genes exhibited similar susceptibility. For the 25 main rice varieties in Guangdong, only 20% contained one or two resistance genes. The frequencies of Xa7, Xa4, and Xa3 were 4%, 8%, and 12%, respectively, while no other resistance genes were detected. Only 4% of the main varieties carried two resistance genes. Most of the 25 varieties were susceptible to the representative strains from Guangdong's pathotypes, with resistance frequencies generally low. Only Guang 8 You 2168, carrying Xa4 and Xa3, exhibited a resistance frequency of 20%, while other varieties had resistance frequencies below 10%.
Currently, most of the new and main rice varieties in South China lack bacterial blight resistance genes or effective gene combinations, leading to widespread susceptibility and an escalating threat from bacterial blight. However, resistance increases with the number of resistance genes. Breeding rice varieties with multiple resistance genes is a promising strategy to address the evolving virulence of bacterial blight. Xa23, Xa7, Xa4, xa8, Xa21, Xa3, and Xa1 contribute to enhancing resistance, with Xa23 and Xa7 standing out as particularly effective and widely applicable resistance genes for future breeding in South China.
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| 科 Family | 属数 Number of genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) | 属 Genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) |
|---|---|---|---|---|---|---|
| 鹅膏菌科Amanitaceae | 2 | 11 | 5.26 | 鹅膏菌属 Amanita | 10 | 4.78 |
| 小菇科 Mycenaceae | 2 | 12 | 5.74 | 丝盖伞属 Inocybe | 5 | 2.39 |
| 多孔菌科 Polyporaceae | 8 | 14 | 6.70 | 蜡蘑属 Laccaria | 5 | 2.39 |
| 红菇科 Russulaceae | 3 | 23 | 11.00 | 小皮伞属 Marasmius | 6 | 2.87 |
| 小菇属 Mycena | 11 | 5.26 | ||||
| 光柄菇属 Pluteus | 5 | 2.39 | ||||
| 红菇属 Russula | 17 | 8.13 | ||||
| 栓菌属 Trametes | 5 | 2.39 |
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