KULDEEP SINGH DANGILAXMI PRASANNA, B2020-09-302020-09-302018D10,322https://krishikosh.egranth.ac.in/handle/1/5810152162Bacterial blight and blast diseases limit rice production in many rice growing areas significantly. Breeding for tolerance to both the major diseases of rice is the economically feasible and environmentally friendly option for managing them. Due to the inherent nature of many rice growing soils in terms of fixing phosphorus (P) to nonavailable form and due to increasing cost of phosphatic fertilizers, a significant proportion of rice growing soils have limiting levels of P and hence are poor in productivity. Breeding for tolerance to low soil phosphorous assumes great significance in such soils. MTU1010 (also known as Cotton Dora Sannalu) is a mega variety of rice grown in many parts of India including Telangana. MTU1010 is highly susceptible to bacterial blight and blast diseases and does not have tolerance to low soil P conditions. Keeping in view these points, the present study entitled “Phenotypic and marker assisted selection for combining the traits; tolerance to low soil phosphorous, resistance a gainst bacterial blight and blast into the elite rice variety, MTU 1010” was carried out with an objective to combine the major QTL associated with tolerance to low soil phosphorus (P) and the major bacterial blight and blast resistance genes, Xa21 and Pi54, xiii respectively into the genetic background of MTU1010 through marker-assisted breeding coupled with phenotype-based selection for agromorphological traits specific for MTU1010. An improved breeding line (i.e. NIL) of MTU1010 (RP5973-20-9-8-24-12-7), possessing tolerance against low soil P conferred by Pup1 (developed by ICAR-IIRR (Anila et al., 2014)) was used as the female parent for improving low soil P tolerance and a breeding line of the high-yielding rice variety, Akshayadhan named RP6132, possessing the major, broad spectrum resistance genes against bacterial blight (i.e. Xa21) and blast (i.e. Pi54) was used as the male parent in the present study. In order to combine the three traits mentioned above, a cross was carried out between NIL of MTU1010 (RP5973-20-9-8-24-12-7) and NIL of Akshayadhan (RP6132) during kharif 2016. At each generation, the resultant F1, F2 and F3 obtained were screened through foreground selection for confirmation of presence of target trait specific genes/QTL, viz., for low P tolerance (Pup1), bacterial blight resistance (Xa21) and blast resistance (Pi54). Foreground selection was carried out with co-dominant CAPS marker, K20-2 for identifying the presence of Pup1, gene specific co-dominant markers viz., pTA248 and Pi54-MAS for checking the presence of Xa21and Pi54 respectively. In F1 generation, 76 plants heterozygous for all the three target traits were identified through analysis with the marker(s) specific for the target gene and they were then forwarded to F2 generation by selfing. In F2 generation, 15 plants homozygous for the three target traits were identified based on foreground selection using the codominant markers mentioned above. The 15 homozygous F2 plants (possessing Xa21, Pi54 and Pup1) were selfed to F3 generation and the F3 lines were screened for their resistance against bacterial blight in the field, blast in uniform blast nursery and low soil P tolerance in low P plot. Analysis of variance among the F3 lines in the present study, revealed the presence of significant difference between the parents and breeding lines for days to fifty percent flowering, plant height, number of productive tillers, panicle length, root length, root volume, dry root weight, thousand grain weight, grain yield per plant, P content in shoots and roots under low soil P condition, but significant difference was not found for dry shoot weight. Stress indices like stress tolerance index, tolerance index, yield reduction ratio, yield index, stress susceptibility index, yield stability index and percent yield reductions were worked out based on the yield under normal condition and yield under low soil P condition. Breeding lines with Pup1 possessed high YI value than xiv RP6132. In particular, the breeding line LPK 49-1-21 (possessing Pup1, Xa21 &Pi54) were observed to have lower percent of yield reduction under low soil P condition followed by the other breeding lines possessing Pup1, All the 15 F3 lines were also observed to be resistant to bacterial blight and blast through phenotypic screening and possessed grain yields and grain quality equivalent to or better than the MTU1010 NIL. Two breeding lines viz., LPK 30-18-16 and LPK 49- 15-22 respectively, exhibited good performance with high level of resistance to all the three stresses viz., BB, blast and low soil P and possessed high yield under both normal soil P and low soil P with highly desirable long slender grain type like MTU1010. The results obtained in the preent study indicate the success of the strategy of combining marker-assisted breeding with phenotypic selection and the two lines mentioned above are expected to perform well in areas prone to the two diseases and also in problematic soils with low soil phosphorous levels. Cultivation of the biotic and abiotic stress resistance/tolerant breeding lines developed in this study would be of great advantage in BB and blast endemic areas and also in low P affected rice growing areas, particularly upland conditions in the country and can be helpful to expand the area under MTU1010.EnglishThesis