| Rice blast, caused by Magnaporthe grisea (Hebert) BArr, is one of the most devastating plant diseases, infecting rice crops all over the world. It has been proved that breeding and planting disease-resistant cultivars is the most economical and efficient means to control this disease. Screening and utilization of rice resources resistant to blast is the foundational measure to breed resistant varieties. The total differences of agronomic characters and blast resistance between 48 fundamental rice resources and 47 improved rice resources resistant to rice blast was compared by using the multiple covariance analysis. Principal component analysis as well as cluster analysis was performed on agronomic characters of the 95 tested resistance resources. The result indicated that the blast resistance of the fundamental resistance resources and the improved resistance resources was not significantly different, but their agronomic characters were extremely significantly different. Some agronomic characters, such as days of sowing to heading, effective panicles per plant, filled spikelets per panicle, seed setting, 1000-grain weight, grain weight per plant and grain width, had highly genetic improvement. The 95 resistance resources might be divided into 2 groups by using principal component analysis and cluster analysis based on agronomic characters. Groupâ… had 47 resources, including 3 subgroupsâ… 1,â… 2,â… 3, with 27.66% of the foundation resistance resources and 72.34% of the improved resistance resources. Subgroupsâ… 1 had larger panicle, few panicles per plant with short-type seed. Agronomic characters of subgroupsâ… 2 were harmonious with high grain weight per plant. Subgroupsâ… 3 had high 1000-grain weight and long-type seed, such as HR17-92-332-2,HR17-TTP-17 with good grain quality and restoring character to three male-sterile lines. Groupâ…¡had 48 resources, including 4 subgroupsâ…¡1,â…¡2,â…¡3,â…¡4, with 72.92% of the foundation resistance resources and 27.08% of the improved resistance resources. Based on the target of breeding and the principle of parent supplementary, Groupâ… should be used as the most important resource for breeding rice varieties resistant to rice blast.In addition, three pairs of primer, RGAl(XLRR-for / XLRR-rev), RGA2(XLRR-inv1 / XLRR-inv2), RGA3(NLRR-for / NLRR-rev) designed and synthesized according to the conserved domains of plant resistance gene were used for analyzing RGA-PCR of the 47 rice varieties, including some resistance resources and restoring lines. The result showed that RGA banding patterns produced by the three primers revealed a high level of polymorphism. A total of 447 bands were amplified by the 3 pair primer, while 348 bands (about 77.85%) were polymorphic, it indicated great diversity in RGA-PCR maps when one rice cultivar was amplified by different primers, the number of bands is from 0 to 9. Clustering analysis showed that the 47 varieties could be classified into 8 groups by RGA1 at 0.70 similarity coefficient, 5 groups by RGA2 at 0.66 similarity coefficient, 9 groups by RGA3 at 0.56 similarity coefficient and 13 groups by 3 pair primers all at 0.68 similarity coefficient, respectively. Clustering result showed that the types of Rice RGA are very abundance, there is no completely uniform group and it also showed that the degree of genetic diversity of resistance is low and the genetic background is obviously diversity. Finally, the strategies of improvement and utilization of rice resistance resources were also discussed. |
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