Introgression of Bacterial Blight Resistance Genes (Xa21, xa13 and xa5) into CB 174 R, an Elite Restorer Line in Rice

Rice (Oryza sativa L.) is an important staple cereal food crop for half of the world populations. Bacterial blight (BB) caused by Xanthomonas oryzae pv. oryzae (Xoo) is one of the most destructive disease across rice-growing regions. CB 174 R is an elite restorer line involved in popular medium duration grain quality hybrid CORH 4, which was highly susceptible to BB. The IRBB 60 possess three resistance genes [one dominant (Xa21) and two recessive genes (xa13 and xa5)] were used as a donor parent to introgress into CB 174 R through marker assisted breeding. The F₁ hybrid CB 174 R × IRBB 60 showed polymorphism for all three genes were tagged and selfed for generation advancement through marker assisted selection. A total of 110 F­₂ individuals of CB 174 R × IRBB 60 was genotyped using two functional (xa13 and xa5) and one flanking (RM 21) markers. Results from our study found three (Xa21+xa13+xa5) and two (Xa21+xa13 or Xa21+xa5 or xa5+xa13) genes introgressed combinations in different F­₂ individuals through foreground selection, thus could be followed until to find homozygous combinations. Among observed genes combinations, BB susceptibility was observed in the absence of Xa21 gene or recessive conditions of xa5 and xa13 genes. The genes introgressed individuals showed broad spectrum of resistance against virulent isolate under field conditions. The identified homozygous/heterozygous individuals forwarded to next cycles of breeding to fix homozygous conditions for all three genes with an improved agronomic performance background, and thus could be used as a donor source for future rice breeding programme.