| The bacterial blight (BB) and blast, two of most serious rice diseases, have been leading to great damage of production and even resulting in no harvest in rice. It has been a tremendous danger to rice production for a long time. Developping disease resistant varieties through molecular marker-assisted selection (MAS) is an effective strategy to reduce this danger, which is also the important part of rice breeding targets for high prodution, high quality and multi-resistance. And there will be far-reaching meaning in practice.9311, the male parent of a super-hybrid rice, 'Liangyoupeijiu', which is susceptible to BB, was used as recurrent parent, and IRBB21 (Xa21) as donor of bacterial blight resistant gene. The Xa21 gene was introgressed into 9311 by crossing followed three backcrossing, and selfing for two times. 44 lines (BCaFa) were obtained. The foreground selections were conducted by a linked marker, pTA248, and a co-segregated STS marker, MXA21. The results showed that 4 lines designated as M071, M082, M086 and M087 were homozygous for Xa21 gene, 8 lines were heterozygous at Xa21 locus. The BB resistances of selected lines were identified by artificial inoculation with Philippine Xoo (Xanthomonas oryzae pv. Oryzae) race 6, PX099. The M071 and M082 were resistant to BB, with a same resistance degree as IRBB21, and the resistance of M086 and M087 were between the level of R (Resistance) and MR (Middle Resistance).248 SSR (simple sequence repeat) primers were filtrated for the polymorphism between parents 9311 and IRBB21. 76 polymorphic SSR markers were found. The proportion of polymorphism was 30.65%. The selected four lines, M071, M082, M086 and M087 with BB resistance, were analysised by these markers for comparing genetic background with recurrent parent. The 73.68% ~ 88.16% of genetic background in selected lines were recovered back to the recurrent parent; the recover proportion could reach to 92.11% if including the heterozygous loci. The results of the agronomic trait comparision were similar to results of molecular marker analysis. The lines, M086 and M087, were more similar to 9311 than lines, M071 and M082, in heading phase. Except for the improvement of BB resistance for F1, there was no obvious difference between F1 (Peiai64S/M086) and Liangyoupeijiu (control) for their agronomic performance. Although the performance of M071 is still some difference from 9311, the recurrent parent, the heterosis in combination is higher than other lines. M071 may have more applying potential in breeding program.There remains danger of resistance defeated for using single resistant gene in varieties of widely planted. In order to develop the multiple and high resistance varieties,MAS is a good method for pyramiding multi-gene with different type of resistant characters. The breeding line CBB23 contains resistant gene Xa23 to rice bacterial blight, and another line BL123 contains three blast resistant genes, Pil, Pi2 and Pi3. The crossing was made between these two parents, and self-seeds of F2 genration were obtained. The seedling of F2 population was screened for blast by inoculation. The remained plants, which were resistance to blast, were further identified by linked markers for resistant genes. The Xa23 gene was selected by PK3 and PK4 markers at each side. Pil, Pi2 and Pi3 were selected by markers of R10, AP22 and G103, respectively. Several pyramiding lines with different multiple resistant genes were obtained. The pyramiding lines were inoculated with PXO99 strain, the lines showed the same resistance level to BB as CBB23.The pyramided lines with blast and BB resistances could be used as multiple resistant rescources in breeding program. It may increase the effectivity of breeding program and shorten breeding time in introgressing multiple resistant genes into aliet breed lines. |
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