Development of bacterial blight resistant thermosensitive genetic male sterile (TGMS) lines for hybrid rice (Oryza sativa L.) production

The genetic variability among restorers, maintainers (B), thermo-sensitive genetic male sterile (TGMS) and other advanced breeding lines of rice (Oryza sativa L.) were determined using 64 microsatellite loci spanning the 12 chromosomes of the rice genome. Unweighted Pair Group Mean Arithmetic (UPGMA) cluster analysis revealed that B lines and TGMS of both IRRI [International Rice Research Inst., Los Baños, Laguna, Philippines] and PhilRice [Philippine Rice Research Inst., Muñoz, Nueva Ecija, Philippines] were distinct in terms of genetic background. B lines of IRRI clustered at 59.2% genetic similarity and are separated from the B lines of PhilRice except for IR73328B and IR78367B. The TGMS materials, including IR68301s, IR73827-23s and IR73834s, grouped at 76.7% genetic similarity. IR73827-23s and IR73834s showed 96.4% genetic similarity in 64 loci and 129 alleles. TGMS1 exhibited 63.5% similarity with the TGMS lines from IRRI while TGMS4 and TGMS6 clustered at 90.1% similarity. All 61 parental cultivars were susceptible to X. oryzae pv. oryzae race 6, PXO99. IR62161-184-3-1-1-2R, pollen parent of NSIC 114H, demonstrated high level of resistance to Xoo race 10, PXO341 including IR68897B, IR79123B, IR78378B, PR3B, IR68301s (TGMS) and three advanced breeding lines. TGMS1, which showed susceptibility to PXO99 and PXO341, was used as recipients in pyramiding Xa4, Xa7 and Xa21 to develop bacterial blight-resistant 2-line hybrid. Phenotypic screening of 1,364 F2 segregating plants against PXO61,PXO86 and PXO99 demonstrated that the xa5 present in AR32-19-3-3 is involved in the large number of F2 plants resistant to PXO61. Genotyping analysis using M5F/R and Xa21F/R markers identified F2 plants no. 450, 473 and 700 homozygous for Xa7 and Xa21 alleles. These plants were unable to produce seeds under greenhouse conditions. Plants no. 450 and 700 exhibited fertility reversion in phytotron and are considered potential BB-resistant TGMS materials.