Marker-Assisted Pyramiding of Genes Conferring Resistance Against Bacterial Blight and Blast Diseases into Indian Rice Variety MTU1010

Abstract: Two major bacterial blight (BB) resistance genes (Xa21 and xa13) and a major gene for blast resistance (Pi54) were introgressed into an Indian rice variety MTU1010 through marker-assisted backcross breeding. Improved Samba Mahsuri (possessing Xa21 and xa13) and NLR145 (possessing Pi54) were used as donor parents. Marker-assisted backcrossing was continued till BC₂ generation wherein PCR based functional markers specific for the resistance genes were used for foreground selection and a set of parental polymorphic microsatellite markers were used for background selection at each stage of backcrossing. Selected BC₂F₁ plants from both crosses, having the highest recoveries of MTU1010 genome (90% and 92%, respectively), were intercrossed to obtain intercross F₁ (ICF₁) plants, which were then selfed to generate 880 ICF₂ plants possessing different combinations of the BB and blast resistance genes. Among the ICF₂ plants, seven triple homozygous plants (xa13xa13Xa21Xa21Pi54Pi54) with recurrent parent genome recovery ranging from 82% to 92% were identified. All the seven ICF₂ plants showed high resistance against the bacterial blight disease with a lesion lengths of only 0.53-2.28 cm, 1%-5% disease leaf areas and disease scoring values of ‘1’ or ‘3’. The seven ICF₂ plants were selfed to generate ICF₃, which were then screened for blast resistance, and all were observed to be highly resistant to the diseases. Several ICF₃ lines possessing high level of resistance against BB and blast, coupled with yield, grain quality and plant type on par with MTU1010 were identified and advanced for further selection and evaluation.