Athira Rajan P V creator Rose Mary Francies (Guide) text Vellanikkara Department of Plant Biotechnology, College of Agriculture 2023 monographic xi, 112p. Rice variety Jyothi (PTB 39) is one among the most preferred and widely cultivated variety across Kerala. Despite its widespread popularity, the cultivar is highly susceptible to bacterial blight (BB) caused by Xanthomonas oryzae pv. oryzae (Xoo). Considering its efficiency, economic viability and eco-friendliness, host-plant resistance has been advocated as the best option to combat the BB pathogen. Advancements in the field of molecular biology such as marker-assisted selection (MAS) have paved ways for pyramiding multiple R-genes into a single genotype. In this context, efforts to introgress three R-genes (xa5, xa13 and Xa21) imparting resistance to BB into the rice variety PTB 39 (Jyothi; recurrent parent) from Improved Samba Mahsuri (ISM; donor parent) through marker assisted selection, was initiated at the College of Agriculture, Vellanikkara. The present study was formulated to identify BC2F1s and BC1F2s pyramided with the R- genes conferring resistance to bacterial blight (xa5, xa13 and Xa21), using functional marker as well as R-gene linked Sequence tagged site (STS) markers. Morphological characterisation of the population was also envisaged. Foreground selection in five BC2F1s along with the parents was done using good quality DNA isolated in order to identify plants introgressed with the three targeted R-genes. Markers RG556 and xa5SR/R linked to xa5, RG136 and xa13 prom linked to xa13 and pTA248 linked to Xa21 were used. Foreground profiling with RG556 and xa5SR/R resulted in monomorphic banding pattern in the experimental population revealing the endogenous presence of R-gene xa5. Screening of BC2F1s using RG136 and xa13-prom and pTA248 revealed the presence of amplicons similar to that found in the recurrent parent Jyothi in the backcross individuals, implying the absence of R-genes xa13 and Xa21 in BC2F1s. The results thus pointed out that the BC2F1s possessed only one R-gene i.e., xa5. Morphological characterisation of BC2F1s indicated that population exhibited similarity towards the recurrent parent Jyothi. Foreground profiling of BC1F2 (132 Nos.) and parents with markers RG556 and xa5SR/R linked to R-gene xa5 resulted in monomorphic banding pattern across the experimental population. This indicated the endogenous presence of the R-gene xa5 in BC1F2s as well as the parents. Presence of R-gene xa13 was evident in 35 BC1F2s i.e., five progenies of BC1F1 Plant No. 9.7, twenty-four progenies of BC1F1 Plant No. 9.15 and six progenies of BC1F1 Plant No. 9.17, on screening with R-gene xa13 linked markers RG136 and xa13-prom. Twenty-five R-gene pyramids, out of the 35, were deduced to be heterozygous at xa13 R-gene locus (xa5xa5+xa13Xa13), while 10 were found to be homozygous (xa5xa5+xa13xa13). Foreground selection for the R-gene Xa21 using pTA248 helped identify 31 BC1F2s introgressed with R-gene Xa21. Among them, 18 were found to be heterozygous (xa5xa5+Xa21xa21) and 13 were homozygous (xa5xa5+ Xa21Xa21), at the R-gene locus (Xa21). The foreground selection thus helped delineate 42 R-gene pyramids among the 132 BC1F2 individuals. Among them, twenty-four were identified to be 3-R-gene pyramids. This included four individuals (Plant No. 9.15.15, Plant No. 9.15.20, Plant No. 9.15.39 and Plant No. 9.17.8) homozygous at all three R-gene loci (xa5xa5+xa13xa13+Xa21Xa21). Background selection of the 24 three-R-gene pyramids identified was done using 52 SSR markers found to be polymorphic between the donor parent ISM and recurrent parent Jyothi. Results revealed the presence of wide variability among the backcross individuals with respect to segregation of marker loci as well as genome recovery from recurrent parent (RPGR). The maximum recovery of 61.90 per cent was found in Plant No. 9.15.59 followed by 59.40 per cent in Plant No. 9.17.8. The least recovery was observed in Plant No. 9.15.42 (27.90 %). The RPGR per cent for the four 3-R-gene pyramids homozygous at all three loci were 41.50 (Plant No. 9.15.15), 47.30 (Plant No. 9.15.20), 48.60 (Plant No. 9.15.39) and 49.40 (Plant No. 9.17.8). In general, the BC2F1s exhibited more similarity to the recurrent parent Jyothi rather than the donor parent for yield attributes and yield. However, none of the BC2F1s and BC1F2s flowered earlier than Jyothi and no individuals were found to flower as late as the donor parent. Except in case of days to flowering, the average estimates of yield attributes and yield of BC1F2s were less than that observed in the recurrent parent Jyothi, but higher than that observed in donor parent ISM. Two R gene pyramided BC1F2 individuals possessed white coloured decorticated kernels similar to the donor parent In spite of lower average estimates for yield attributes and yield, transgressive segregants were also observed among the BC1F2s. Negatively skewed platykurtic distribution was observed in traits like plant height, leaf length, panicle length, spikelets per panicle, grains per panicle, 100 grain weight, grain length and width, and decorticated kernel width, while positively skewed platykurtic distribution was evident for all other traits viz., days to flowering, total tillers, productive tillers, leaf width, and grain yield per plant. The decorticated kernel length was the only trait that exhibited a leptokurtic distribution and had registered negative skewness. Hence, it can be inferred that the trait kernel length is governed by a few segregating genes with majority of them exhibiting decreasing effects and dominance-based interactions. All the forty-two R-gene introgressed BC1F2s were selfed to yield seeds (3897 Nos.) of BC1F3 generation. The BC1F3 progenies of the 3-R-gene homozygotes need to be further backcrossed to the recurrent parent to aid higher recovery of the recurrent parent genome. This will eventually lead to the development of an Improved Jyothi with durable resistance to BB pathogen. These stable R-gene introgressions can also serve as donors in BB resistance breeding programmes in rice. In addition, the transgressive segregants could serve as potential breeding materials for development of high yielding genotypes. MSc Rice variety jyothi Plant biotechnology Bacterial blight resistance genes 660.6 ATH/MA PG https://krishikosh.egranth.ac.in/handle/1/5810224688 https://krishikosh.egranth.ac.in/handle/1/5810224688