Improvement Of The Rice Resistance To Rice Bacterial Blight By Molecular Markers-assisted Selection

Rice is an important cereal crop. Bacterial blight (BB) caused byXanthomonas oryzae pv. Orzae(Xoo.) is one of the most destructivediseases of rice throughout the world. Furthermore, BB also affects ricequality. The incorporation of resistance genes into rice cultivars is the mosteconomic and effective method to control this disease. Molecularmarker-assisted selection (MAS) was already widely used to melioratesome characters of crops. Molecular markers, including makers that nearthe target gene or in the gene of interest, were identified by currentbiological strategies and used to improve rice disease resistance. Theadvantage of molecular markers is that a particular trait can be selected asearly at the embryo stage, There is no longer a need for the organism todevelop to a special stage at which the trait can be observed, in some casesit may take many years. At present, more than 20 resistant genes to BB were identified in rice.Xa23 gene was identified by Zhang Qi, which was a dominat gene andcan conffered rice high, broad spectrum and whole growth stage resistanceto all tested BB race. So Xa23 gene has bright prospect in the improvementof the rice resistance to BB. Two RAPD markers(RpdH5 and RpdS1184)and two SSR markers(RM187 and RM206) which linked to Xa23 gene weredeveloped by Pan Haijun and Zhang Qi, The genetic distance between themolecular markers: RpdH5, RpdS1184, RM1 87 and RM 206 and theXa23 gene were7.0 cM,7.6cM,7.1cM and 1.9cM, respectively. It hasthe possible to improve rice resistance to BB through MAS.The Xa23 gene was introduced to rice restorer line C418, Minghui86and sterile line Peiai64s by MAS through traditional backcross breedingand MAS. PCR analysis and the field bioassay indicated that C418-Xa23,Minghui86- Xa23, PA64- Xa23 harbered Xa23 gene and the exhibitedimproved resistance to BB. New indica hybrids were obtained also bycombinated these rester line harbering Xa23 gene with Jiazao312A,Peiai64s, Xiushui110A, 666A and 9311 field bioassay indicated that thebybrids had high resistance to BB.