Improvement Of Blast Resistance Of Three-line Rice Maintainer Line G Ruanhua B

In this experiment,the disease resistance of G Ruanhua B,a high quality Indica maintainer,was rapidly improved by using the technology of molecular marker assisted breeding.G Ruanhua B has the characteristics of good rice quality,strong aroma,large ears and grains,and good yield,but its resistance to rice blast is poor.In order to ensure the development and safe production of this combination,and to verify whether the site-directed rapid improvement technology using molecular marker-assisted breeding can quickly achieve the purpose of the experiment,the blast resistance of rice was improved,while the original fragrance and excellent rice quality of G Ruanhua B could be greatly retained in the improvement.In this study,H281,which is like the quality trait of G Ruanhua B,complementary to some agronomic traits and carries the rice blast resistance gene,was selected as the donor parent.At the same time,single plants with antibody genes were detected at early seedling stage by molecular marker-assisted breeding technology,and single plants with similar appearance of Agronomic Traits to G Ruanhua B were selected at heading stage and text crossed with G Ruanhua A.To improve the selected new strains of G Ruanhua B,the resistance of the improved strains was compared when the traits were relatively homozygous.At the same time,the traits of the improved relatively homozygous strains were compared with those of the original G Ruanhua B,such as quality and sterile line maintenance.The test results are as follows:1.Molecular markers closely linked to rice blast resistance genes Pik-H4 and Pi-2 were used for screening in combination with strict field agronomic trait screening and maintenance line detection.,multi-generation backcross breeding resulted in 2 populations of BC₁F₄,3populations of BC₂F₃ and 2 populations of BC₃F₃ carrying two homozygous target resistance genes.Therefore,the technology of using molecular marker-assisted breeding after introducing resistance genes can quickly obtain improved parents with resistance.2.The results of rice blast resistance test showed that the disease resistance grade of G Ruanhua B was high susceptibility（HS）,and the frequency of comprehensive resistance spectrum was 18.8%.In this experiment,all the improved materials of different backcross generations reached resistance（R）,and the frequency of disease resistance was more than93.8%.The results showed that molecular markers were used to rapidly improve the resistance of G Ruanhua B,improve the grade of blast resistance,increase the frequency of disease resistance,and effectively shorten the duration of resistance breeding.3.According to the comparison of agronomic traits and quality traits in the field,some agronomic traits of the improved lines were different from the original parent G Ruanhua B.The plant height became shorter and the sword leaf became shorter.Except for individual materials,there was no significant difference between the quality traits of the improved materials and G Ruanhua B.The excellent traits of G Ruanhua B were basically retained,and the aroma of rice was maintained.It indicated that the improved lines by molecular marker-assisted breeding technology could basically retain the main agronomic traits of G Ruanhua B,and maintain the original excellent rice quality and aroma as much as possible by genetic testing.4.The infertility grades of improved population BC₁F₄ were all semi-sterile,the L3 and L4 materials in improved population BC₂F₃were semi-sterile,the L5 materials had reached total sterility,and the improved population BC₃F₃ reached total sterility.It indicated that molecularly modified maintainer G Ruanhua B was affected by the donor parents,and the maintainability was gradually restored with the increase of backcross generations.It was difficult to achieve the purpose of this experiment by using molecular marker-assisted breeding technology in one test cross,and the purpose of this experiment must be achieved after multiple backcrosses.5.According to SNP gene chip detection,the background recovery rate of improved population BC₁F₄was 74.02%～77.77%;the background recovery rate of improved population BC₂F₃ was 81.09%～87.85%;the background recovery rate of improved population BC₃F₃was 91.27%～92.59%.This indicates that with the increase of backcross generations,the higher the similarity between the background of the improved material and G Ruanhua B,the higher the degree of recovery,and further verifies the fourth result.