| Summary: | 碩士 === 國立中興大學 === 農藝學系所 === 100 === TK9 is one of the most popular japonica type rice varieties in Taiwan because of its good plant type, stable yield and excellent grain quality. However, TK9 is very susceptible to bacterial blight disease (BBD) causing by Xanthomonas oryzae pv. Oryzae (Xoo). In this study, markers assisted backcross (MAB) strategy was conducted to introgress Xa genes into TK9 to improve its BBD resistance. Two indica varieties, IRBB62 (Xa4, Xa7 and Xa21) and IRBB66 (Xa4, xa5, Xa7, xa13 and Xa21) containing various BBD resistance genes (Xa) were used as the resistance donor for this purpose. Two crosses designated as 962 (TK9/IBB62) and 966 (TK9/IRBB66) were obtained by crossing the recurrent parent TK9 with IRBB62 and IRBB66, respectively. F1 hybrids were backcrossed with TK9 to proceed the generation, PCR based markers were applied to perform foreground and background selection in each generation, and accompany with phenotypic selection by pathogen challenge and agronomical trait investigation. Genotype of each BC plant was consistent with the lesion length of pathogen inoculation suggested that the more Xa genes pyramided the higher BBD resistance. Plants from backcrossing contain higher recurrent parent genome (RPG) show more similarity to TK9 phenotype. So far, we obtained BC3F1 progenies with RPG higher than 90％ and show good plant type as of TK9. With one self-crossing to reach BC3F2 and homozygous Xa genes, we can breed a new TK9 variety with BBD resistance and good grain quality. This study demonstrates that MAB is an efficient method for improving disease resistance without trait penalty within four years.
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