Education & Training

Blast Resistance Genes Identification, Genetic Diversity of Rice Varieties and Resistant Resources Screening

Update time: 07/23/2010

Rice blast, caused by Magnaporthe grisea (Hebert) Barr, is the most devastating rice crop disease in the world. It has been proved that breeding and planting diease-resistant cultivars is the main efficient ways to control rice blast disease. Marker assisted selection closely linked with the resistance genes could accelerate the resistance parent strain screening and identification of resistance genes and greatly improve the efficiency of breeding cultivar with durable blast resistance varieties.

This study focous on identification of major blast resistance genes Pita/Pib by the establishment of specific molecular markers, and further on the resistance in the field, resistance spectrum of inoculation grisea resistance, main agronomic traits of the rice sources from CIBCAS(Chengdu Institute of Biology, Chinese Academy of Sciences). The genetic diversity and genetic background of some resistant resources and three-line parents of indica hybrid rice were also analyzed by microsatellite markers to utilize and breed diseases-resistant varieties. It would provide a reference to the higher heterosis hybrid combinations. The major results are as follows:

1. Identification of the major blast resistance genesPita and Pib by the specific dominant molecular markers established by Pita/pita and Pib/pib alleles. The results show that Pita genes was found in 5 rice cultivars, such as IR22866-124-3-3 and R747; the resistance alleles Pib was found in 7 rice cultivars, for example 4607, 4484 and Chenghui 177.

2. Investigation and study on blast resistance test, the main agronomic traits in tested rice materials.The DSLB and DSPB of Gumei-1, Gumei-3, Tetep, IR25865-124-3-3, IR47751-1-3-2, Chenghui177 and other materials were Higher Restance(RH)or Restance(R), to be considered good blast resistance sources. The resistance spectrum of 10 varieties were above 80%. Furthermore, the major agronomic traits of resistance rice were statistically analyzed. The results showed that there are greatly differences in agronomic traits among them.

3. The genetic diversity and genetic background of some resistant resources was detected by 19 pairs polymorphic SSR primers closely linked with blast resistance genes. The PCR amplification products were reproducible, highly specific and polymorphic. Cluster analysis showed that 30 rice materials could be classified into 6 groups. It also provided evidences of genetic diversity of blast resistance and significant genetic background.

4. 24 three-line parents of indica hybrid rice, were used to analyze their genetic diversity and genetic relationship by using 26 polymorphous primer pairs slected from 110 SSR which dispersed on 12 chromosomes in rice. Those primers detected 116 alleles from all the 24 parents. The alleles number might range from 2 to 7 with the average 4.4. The PIC (Polymorphism index content) value of the polymorphic markers ranged from 0.068 9 to 0.803 6, with an average of 0.603 4. The expected heterzygosity (He) ranged from 0.081 6 to 0.829 8 and the average was 0.616 9. However, Shannon's information index (I) ranged from 0.173 2 to 1.791 3 with average of 1.160 0.

Furthermore, according to the results of cluster analysis by UPGMA method, the 24 parents materials were classified into three groups by microsatellite markers, and the parents among the groups showed relatively large genetic variation, which could

be used to identify the relationship among the parents, and also to predict the heterosis of new materials by molecule markers assisted selection. The results provide a good reference to the choice of higher heterosis hybrid combinations in rice breeding.

Keywords  Rice (Oryza sativa L.); Blast Resistance Gene; Resistance Identification; SSR Marker; Genetic Diversity