PhD

Salinity is a major abiotic stress affecting rice productivity. The research work titled “Introgression of Saltol gene into rice variety Sreyas” was conducted to introgress QTL Saltol into rice variety Sreyas using identified donor FL478 through marker-assisted backcross breeding.
The research work included hybridization of the variety Sreyas (MO-22) with the donor FL478 to transfer the Saltol locus. Polymorphism assay of foreground, recombinant and background SSR markers was conducted to identify the markers polymorphic between both parents. In vitro phenotyping of F1 plants under 12 dS m-1 (NaCl) and genotypic foreground selection of survived plants was done to select plants for the breeding programme. In vitro phenotyping of BC1F1 plants under 12 dS m-1 (NaCl) and genotypic foreground, recombinant and background selection of survived plants was carried out to identify the lines carrying Saltol QTL with adequate genome recovery. These plants were backcrossed with the recurrent parent Sreyas to advance to the next generation. In vitro phenotyping of BC2F1 plants under 12 dS m-1 (NaCl) and genotypic foreground, recombinant and background selection of survived plants were done to identify the most promising lines.
The performance of the parents was compared in stress-free conditions. Parent Sreyas recorded better performance for plant height (96.94 cm) number of productive tillers (8.3), longer panicles (20.75 cm), had bold grains (L/B ratio 2.25) and high yield (26.08 g) with a mean 1000-grain weight of 29.64g. FL478 (73.15 days) flowered earlier than Sreyas (81.45 days) and matured in 123 days with a panicle length of 20.07cm, grain L/B ratio of 3.00. The kernel colour of both genotypes was red.
The polymorphism assay for Saltol-associated markers between Sreyas and FL478 revealed 9 polymorphic markers which were located within 10.8 – 12.3 Mb. The foreground parental polymorphism percentage in 36%. The marker used for foreground selection are RM10711, RM8094, RM10713, RM10720 and RM3412. The markers RM1287 and RM10701 telomeric to the QTL and RM493 and RM10895 centromeric to the QTL are the flanking markers used for recombinant selection. Polymorphism assay for the background markers revealed that 83 markers were polymorphic between the parents (at least 5 per chromosome) with a parental polymorphism percentage of 27.67%.
The F1 population showed a better germination percentage of 86.81% at 12 dSm-1 in comparison to the recurrent parent Sreyas (83.33%) but lesser than the donor parent FL478 (93.33%). Days to germination initiation (1.26) and mean days for completion of germination (6.25) of F1 was intermediate to both parents. The F1 population showed 52.27% survival and an intermediary SES score of 6.49. Foreground genotypic selection resulted in the selection of 16 plants which were forwarded to the next generation by backcrossing with Sreyas.
The BC1F1 and BC2F1 populations showed better salinity tolerance than recurrent parent Sreyas. The mean germination percentage of BC1F1 (86.45%) and BC2F1 (86.79%) populations improved compared to the recurrent parent (83.33%). Days to germination initiation and completion in BC1F1 (1.28, 6.28) and BC2F1 (1.31, 6.32) populations was earlier than Sreyas (1.32,6.36). The mean survival percentage increased substantially in BC1F1 (49.79%) and BC2F1 (40.31%) populations. The mean SES scores which indicate salt injury in BC1F1 (6.63) and BC2F1 (7.25) populations improved as against Sreyas (7.96). The percentage leaf drying, was found to have improved in the backcrossing generations, BC1F1 (89.25%) and BC2F1 (89.83%)) Foreground, recombinant and background selection were used to identify the lines to be selected for the next generation. In the BC1F1 generation, 17 plants survived in the field from which 8 were forwarded to the next generation by backcrossing. In the BC2F1 generation, 24 plants survived in the field from which 13 were selected to be advanced to further generations.
Mean recurrent genome recovery was 62.02% in BC1F1 and 77.8% in BC2F1 populations. The progeny of 19-01-1 and 19-01-14 BC1F1 lines were most promising based on salinity screening parameters. Based on genotypic selection and recurrent genome recovery of BC2F1 population 19-01-1-7 and 19-01-14-5 were identified as promising plants. In the BC2F1 population, the selected plants had an introgressed fragment of 2.49 Mb within Saltol region (10.83 – 13.32Mb) in heterozygous condition.
The selected plants may be backcrossed followed by screening for salinity attributes to identify superior lines.