Jalmagna is a popular deepwater rice variety with farmers of India because of its good yield under waterlogged condition. However, the variety is highly susceptible to bacterial blight (BB) disease. The development of resistant cultivars has been the most effective and economical strategy to control the disease under deepwater situation. Three resistance genes (xa5 + xa13 + Xa21) were transferred from Swarna BB pyramid line, using a marker-assisted backcrossing (MAB) breeding strategy, into the BB-susceptible elite deepwater cultivar, Jalmagna. Molecular marker integrated backcross breeding program has been employed to transfer three major BB resistance genes (Xa21, xa13 and xa5) into Jalmagna variety. During backcross generations, markers closely linked to the three genes were used to select plants possessing these resistance genes and markers polymorphic between donor and recurrent parent were used to select plants that have maximum contribution from the recurrent parent genome. A selected BC3F1 plant was selfed to generate homozygous BC3F2 plants with different combinations of BB resistance genes. The three-gene pyramid and two gene pyramid lines exhibited high levels of resistance against the BB pathogen. Under conditions of BB infection, the three-gene pyramided lines exhibited a significant yield advantage over Jalmagna. The selected pyramided lines showed all agro-morphologic traits of Jalmagna without compromising the yield. The three major BB resistance genes pyramided lines exhibited high level of resistance and are expected to provide durable resistance under deep water situation where control through chemicals is less effective. High similarity in agro-morphologic traits and absence of antagonistic effects for yield and other characters were observed in the best pyramided lines.

Background: High yielding rice varieties are usually low in grain iron (Fe) and zinc (Zn) content. These two micronutrients are involved in many enzymatic activities, lack of which cause many disorders in human body. Bio-fortification is a cheaper and easier way to improve the content of these nutrients in rice grain.Results: A population panel was prepared representing all the phenotypic classes for grain Fe-Zn content from 485 germplasm lines. The panel was studied for genetic diversity, population structure and association mapping of grain Fe-Zn content in the milled rice. The population showed linkage disequilibrium showing deviation of Hardy-Weinberg’s expectation for Fe-Zn content in rice. Population structure at K = 3 categorized the panel population into distinct sub-populations corroborating with their grain Fe-Zn content. STRUCTURE analysis revealed a common primary ancestor for each sub-population. Novel quantitative trait loci (QTLs) namelyqFe3.3andqFe7.3for grain Fe andqZn2.2,qZn8.3andqZn12.3for Zn content were detected using association mapping. Four QTLs, namelyqFe3.3,qFe7.3,qFe8.1andqFe12.2for grain Fe content were detected to be co-localized withqZn3.1,qZn7,qZn8.3andqZn12.3QTLs controlling grain Zn content, respectively. Additionally, some Fe-Zn controlling QTLs were co-localized with the yield component QTLs,qTBGW,OsSPL14andqPN. The QTLsqFe1.1,qFe3.1,qFe5.1, qFe7.1, qFe8.1, qZn6, qZn7 and gRMm9–1for grain Fe-Zn content reported in earlier studies were validated in this study.Conclusion: Novel QTLs,qFe3.3andqFe7.3for grain Fe andqZn2.2,qZn8.3andqZn12.3for Zn content were detected for these two traits. Four Fe-Zn controlling QTLs and few yield component QTLs were detected to be co-localized. The QTLs,qFe1.1,qFe3.1,qFe5.1, qFe7.1, qFe8.1, qFe3.3, qFe7.3, qZn6, qZn7, qZn2.2, qZn8.3andqZn12.3will be useful for biofortification of the micronutrients. Simultaneous enhancement of Fe-Zn content may be possible with yield component traits in rice.

Antioxidant-rich rice is a cheaper way to solve stress-related disorders and other health benefits for the global rice-eating population. Five antioxidant traits, namely, superoxide dismutase, flavonoids, anthocyanins, γ-oryzanol and 2,2′-azino-bis-3-ethylbenzthiazoline-6-sulphonic acid (ABTS) activity were mapped using a representative panel population through association mapping. Potential landraces carrying multiple antioxidant compounds were identified from the population. The population represented four genetic groups and correspondence for presence of antioxidants traits in each group was noticed. The population showed linkage disequilibrium for the studied traits based on the Fst values. A total of 14 significant marker–trait associations were detected for these antioxidant traits. The study validated the QTLs, qANC3 and qPAC12-2 for anthocyanin content and qAC12 for ABTS activity will be useful in marker-assisted breeding. Eleven QTLs such as qTAC1.1 and qTAC5.1 controlling anthocyanin content, qSOD1.1, qSOD5.1 and qSOD10.1 for superoxide dismutase (SOD), qTFC6.1, qTFC11.1 and qTFC12.1 for total flavonoids content (TFC), qOZ8.1 and qOZ11.1 for γ-oryzanol (OZ) and qAC11.1 for ABTS activity were detected as novel loci. Chromosomal locations on 11 at 45.3 cM regulating GO, TFC and TAC, and on the chromosome 12 at 101.8 cM controlling TAC and ABTS activity, respectively, were detected as antioxidant hotspots.

Ranidhan is a popular late-maturing rice variety of Odisha state, India. The farmers of the state suffer heavy loss in years with flash floods as the variety is sensitive to submergence. Bacterial blight (BB) disease is a major yield-limiting factor, and the variety is susceptible to the disease. BB resistance genes Xa21, xa13, and xa5, along with the Sub1 QTL, for submergence stress tolerance were transferred into the variety using marker-assisted backcross breeding approach. Foreground selection using direct and closely linked markers detected the progenies carrying all four target genes in the BC₁F₁, BC₂F₁, and BC₃F₁ generations, and the positive progenies carrying these genes with maximum similarity to the recipient parent, Ranidhan, were backcrossed into each segregating generation. Foreground selection in the BC₁F₁ generation progenies detected all target genes in 11 progenies. The progeny carrying all target genes and similar to the recipient parent in terms of phenotype was backcrossed, and a total of 321 BC₂F₁ seeds were produced. Ten progenies carried all target genes/QTL in the BC₂F₁ generation. Screening of the BC₃F₁ progenies using markers detected 12 plants carrying the target genes. A total of 1270 BC₃F₂ seeds were obtained from the best BC₃F₁ progeny. Foreground selection in the BC₃F₂ progenies detected four plants carrying the target genes in the homozygous condition. The bioassay of the pyramided lines conferred very high levels of resistance to the predominant isolates of bacterial blight pathogen. These BB pyramided lines were submergence-tolerant and similar to Ranidhan in 13 agro-morphologic and grain quality traits; hence, they are likely to be adopted by farmers.

Because it is rich in antioxidant compounds, the staple food of rice provides many health benefits. Four antioxidant traits in rice grain, viz., catalase, CUPRAC, DPPH, FRAP and peroxidase, were mapped in a representative panel population containing 117 germplasm lines using 131 SSR markers through association mapping. Donor lines rich in multiple antioxidant properties were identified from the mapping population. The population was classified into three genetic groups and each group showed reasonable correspondence with the antioxidant traits. The presence of linkage disequilibrium in the population was confirmed from the estimated Fst values. A strong positive correlation of DPPH was established with TPC, FRAP and CUPRAC. A moderate to high mean gene diversity was observed in the panel population. Eleven significant marker-trait associations for antioxidant traits were mapped, namely, qACD2.1, qACD11.1 and qACD12.2 for DPPH; qCAT8.1 and qCAT11.1 for catalase; qFRAP11.1, qFRAP12.1 and qFRAP12.2 for FRAP; and qCUPRAC3.1, qCUPRAC11.1 and qCUPRA12.1 regulating CUPRAC. Co-localization of the QTLs for qACD11.1, qFRAP11.1 and qCUPRAC11.1 were detected, which may act as antioxidant hotspots regulating DPPH, FRAP and CUPRAC activities, respectively, while qACD12.2 and qFRAP12.1 remained close on the chromosome 12. These detected QTLs will be useful in antioxidant improvement programs in rice.

The bacterial blight (BB) disease of rice is a major disease that reduces yield heavily in susceptible varieties. Ranidhan is a late maturing popular rice variety but shows high susceptibility to the disease. Two BB resistance genes were transferred into the variety through a marker-assisted backcross breeding approach. Tightly linked molecular markers were deployed to track the BB resistance genes in the plants carrying the target genes in each backcross generation. Foreground screening detected 17, 16 and 15 progenies to carry the 3 BB resistance genes in BC₁F₁, BC₂F₁ and BC₃F₁ generations, respectively. The selected BC₃F₁ plant was selfed and three different combinations of BB resistance genes were tracked in homozygous state in seven BC₃F₂ plants. The pyramided lines carrying three resistance genes in homozygous conditions were evaluated for BB disease resistance by inoculating with eight virulent Xoo strains. Five pyramided lines carrying two resistance gene combinations (Xa21+xa13 and Xa21+xa5) exhibited enhanced resistance against the BB pathogens. The disease resistance was in the order of Xa21+xa5 < Xa21+xa13 < xa13+xa5 gene combinations in conferring the resistance. The developed pyramided lines were similar to the recipient parent for the majority of the important agro-morphologic and grain quality traits.