Selection For Blast-Resistance Germplasm And Mapping Of Resistance Genes In Dacca6

Dacca6,a local variety from Philippine, was characterized of broad-spectrum and durable resistance to blast. Consequently, we tried to map resistance genes in Dacca6 by backcross populations and anchor target gene-linked markers for subsequent marker-assisted gene pyramiding and cloning. Main research results are as follows:1. 131 rice cultivars coming from all over the world were provided to identify their resistance to seeding, leaf, and spike blast in Shanghang. The results showed that 23.7% identified cultivars were resistant to blast. These cultivars could be used as donor parents for improving resistance to blast in the rice breeding programs.2. In order to evaluate performance of rice blast resistance genes in Fujian Province, 26 monogenic rice lines developed by IRRI, 12 parents ofor hybrid rice planted all over the country and 3 new blast resistance cultivars were inoculated with 86 blast isolates collected from different rice regions of Fujian. The value of resistance genes would be evaluated by calculating resistance frequency(RF),pathogenicity association coefficient(VAC)and resistance association coefficient(RAC). The results showed that the RF of Dacca6 is 81.4% and Dacca6 with complete resistance could be used as resistance donor to improve hybrid rice for resistance to blast.3. The BC₁F₂ populations derived from the cross of Dacca6 with Jin23B were inoculated by two isolates, SM03023 and SH0512. The results showed that blast resistance of Dacca6 was controlled by a single dominant gene. Using a BC₁F₂ population, the blast resistance gene of Dacca6 was mapped between markers RM5529 and RM211, thegenetic distances were 3.8 cM and 4. 1 cM, respectively ,on chromosome 2 by analysis on BSA and RCA. Meanwhile we mixed resistant and susceptible DNA pools of 8 respective BC₁F₂ populations derived from 8 selfed BC₁F₁ resistant plants and analysed the introgression segment on chromosome 2 with 21 SSR polymorphic makers. It showed they all had heterozygous makers in the region of RM211, which means the resistance gene locate near to the region ofRM211, and it was consistent with the results of gene mapping. This study established a close linkage relationship between resistance gene and its molecular markers, which would improve the efficiency of molecular marker assisted breeding and provide a basis for cloning the resistance gene.