Binod Kumar Jena

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.

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.

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.