Marker assisted introgression of genes conferring resistance to bacterial blight and blast into hybrid rice parental line and evaluation of the gene introgressed lines

Abstract

DRR17A is a very fine-grain type wild-abortive cytoplasmic male sterile (WA-CMS) line of rice developed by the Indian Institute of Rice Research, Hyderabad. However, DRR17A and its maintainer line DRR17B are highly susceptible to two of the major rice diseases, bacterial blight (BB) and blast. To improve DRR17B for BB and blast resistance, we have introgressed two major dominant genes Xa21 + Xa33 each conferring resistance against BB and blast (Pi-54 + Pi2) into DRR17B through marker-assisted backcross breeding using Improved samba Mahsuri (for Xa21 gene), FBR1-15 (Xa33), Tetep (Pi54) and C101A51 (Pi2) as the donor parents. PCR-based molecular markers specific for Xa21, Xa33 Pi2 and Pi-54 were used for foreground selection, while parental polymorphic SSR markers were utilized for background selection for accelerating the recovery of the recurrent parent genome. In addition, at BC1F1 generation, molecular markers tightly linked to the fertility restorer genes, Rf3 and Rf4 were used for negative selection to identify foreground selection positive lines devoid of fertility restorer alleles at the two loci. Marker-assisted backcrossing was continued till BC3 generation and at BC3F2, one best plant from all four crosses was selected and intercrossed (IC) to combine the BB and blast genes (i.e. Xa21 + Pi54 or Xa33 + Pi2). At ICF2 generation, one best plant, which was homozygous for the target BB and blast resistance gene (i.e. Xa21 + Pi54 or Xa33 + Pi2) and which resembles the recurrent parent was selected from both the crosses and intercrossed to develop double intercross F1 (i.e. DICF1) to combine all the four target resistance genes into one single genetic background (i.e. Xa21 + Xa33 + Pi2 + Pi54) and selfed to develop DICF2s. Homozygous DICF2 plants were identified with the help of gene-specific markers and advanced further by selfing.