Molecular Mapping And Marker-assisted Selection Of Xa23, A Bacterial Blight Resistance Gene In Rice

Bacterial blight, caused by Xanthomonas oryzae pv. Oryzae (Xoo), is a destructive disease of rice in most rice-growing countries and caused much damage to yield and qulity. The most efficient and economical mean of controlling the disease is the use of variental resistance. Over 20 genes for resistance to bacterial blight have been identified and two of them, Xa21 and Xal, have been isolated. Efforts are underway to isolate several other bacterial blight resistance genes.The Xa23 resistance gene from O.rufipogon is a dominant gene, with high level of resistance at all growth stages and the broadest spectrum of resistance to bacterial blight. Fine-mapping is the first step for map-based cloning of it. A FI population, with 2562 individuals, of JG30/CBB23, was constructed for molecular mapping of Xa23. After screening 1200 random amplified polymorphic DNA (RAPD) primers and 64 combinations of Amplified fragment length polymorphism (AFLP) primers, we found RAPD markers, RpdHS and RpdS1184 and AFLP markers, API87 and AP215, are linked to the Xa23 gene, with genetic distance of 7.0cM, 7.6cM, 6.8cM and 2.4cM, respectively. One marker, CP02662, designed from the sequence of an EST near the site of Xa23, was also found to be linked to the Xa23 gene, with the genetic distance of 2.0cM.The marker-assisted selection (MAS) efficiency of RpdS1184, RM206 and RpdHS was evaluated by using two Fa populations derived fromFengruzhan/CBB23 and Luyouzhan/CBB23. The results showed that the MAS efficiencies of RpdHS and RpdS1184, in population Fengfu23, were 91.0% and 87.3%, respectively, but the MAS efficiency reached as high as 99% when these two markers were co-used. For population Luyou23, the MAS efficiency of RpdHS, RpdS1184 and RM206 were 77.1%, 81.1% and 80.8%, respectively. When RpdHS and RpdS1184 were co-used, the MAS efficiency was 90.3%; When RpdHS and RM206 co-used, the MAS efficiency was 91.3%; When RpdH5, RM206 and RpdS1184 were co-used, the MAS efficiency was 90.8%.