Improvement of bacterial blight resistance of hybrid rice by molecular marker-assisted selection
Chen, S. and Qifa Zhang. 2000. Journal of Huazhong Agricultural University 19(3):183-189.
ABSTRACT This paper described the practice of molecular marker-assisted selection (MAS) in the process of recurrent backcrossing to improve the bacterial blight (BB) resistance of two restore lines of hybrid rice, 'Minghui 63' and '6078', by introgressing Xa21, a broad-spectrum BB resistance gene. A PCR-based MAS system for Xa21 introgressing segment was established. It consisted of a marker representing the Xa21 locus, a marker linked to the Xa21 locus at a distance of 0.8 cM on one side, and a marker at distance of 3.0 cM from the gene on the other side. In the practice of the improvement of Minghui 63, the selection was carried out in tandem in which a recombinant was obtained between Xa21 and one of the makers in BC1F1, and a subsequent recombinant was obtained between the gene and the marker at the other side in BC2F1. The genetic background of Minghui 63 was recovered in BC3F1 using a total of 128 RFLP markers evenly distributed on the 12 rice chromosomes. Thus the improved version of Minghui 63, tentatively referred to as 'Minghui 63(Xa21)', was exactly the same as the original Minghui 63 in the entire genome except for a fragment of less than 3.8 cM in length surrounding the Xa21 locus. A slightly different strategy was adopted for introgressing Xa21 to 6078, a new restorer line. The main difference is that the background selection was carried out mainly in BC1F1, and selections for recombinants were conducted in BC2F1 and BC3F1. Another difference is that AFLP marker was used for background selection. Both of the improved restorer lines, Minghui 63(Xa21) and '6078(Xa21)',showed the same level and spectrum of BB resistance as the donor parent'IRBB21'with artificial inoculation. Minghui 63(Xa21) and '6078(XA21)'also showed the same agronomic performance and combining ability as the original restorer lines when there is no disease stress. The agronomic performance of the improved restorer lines, Minghui 63(Xa21) and 6078(Xa21), and their hybrids was significantly better than the unimproved versiton under field conditions with artificial inoculation.
Key words hybrid rice, restorer line, bacterial blight, Xa21, molecular marker-assisted selection, molecular breeding