YAMINI, N.KRAVI, K2020-10-062020-10-062018D10,341https://krishikosh.egranth.ac.in/handle/1/5810152585Rice (Oryza sativa L.) is used as a staple food for almost one third of the world’s population. In India, 65% of the population depends on rice as their staple food and the country is a huge contributor to the global rice production. However, approximately 52% of global rice production is lost annually owing to the damage caused by biotic stress factors, of which 25% is attributed to the attack by insect pests. Major insect pests and diseases of rice that cause huge economic losses in South Asia are stem borer, brown planthopper (BPH) and gall midge (GM), leaf blast, bacterial blight (BB) and sheath blight. Of these, GM and BB cause major yield losses in rice. Use of resistant varieties has been the most feasible alternative to manage the pests and diseases. However, extensive cultivation of varieties carrying single resistance gene over a large area has resulted in breakdown of resistance making it necessary to deploy alternative approaches. Gene pyramiding has been proved to be a viable approach to achieving broad spectrum durable resistance against several stresses. Also with several advantages, the use of molecular markers to aid in selection of resistant plants is a proven as a precise and viable approach. In the states of Andhra Pradesh and Telangana, GM incidence is mainly observed in coastal regions of Andhra Pradesh and Warangal and Jagtial regions of Telangana. At Warangal, Ragolu and Jagtial regions GMB4M, GMB4 and GMB3 have been reported to occur and pyramiding of the two GM resistance genes i.e. Gm4, Gm8 and two BB resistance genes i.e. xa13, Xa21 would confer the rice plant durable resistance to both of these biotic stresses. Under a DBT Project, at the Institute of Biotechnology (IBT), Rajendranagar in collaboration with Regional Agricultural Research Station (RARS), Warangal, parents were raised conformed and two crosses were made in order to combine all the four resistance genes. MTU1010 (Cotton Dora Sannalu) a leading mega rice variety as well as MTU-IL-1 (Introgression line) having Gm4, xa13 and Xa21 genes, were used as female and crossed with RMSGM-3 (from Akshaydhan background developed by ICAR-IIRR), a homozygous line carrying Gm4, Gm8, xa13 and Xa21 genes. In the present investigation, F2 and F3 generations of these crosses along with parents, were evaluated by combining the molecular screening for resistance genes at IBT, Rajendranagar and phenotypic screening at RARS, Warangal for field level GM and BB resistance, along with selection of superior plants based on phenotypic traits. During Kharif 2016 F2 plants of MTU1010×RMSGM-3 (Cross I) and MTU-IL-1 × RMSGM-3 (Cross II) were raised and screened for field level resistance to GM. AT 50 days after transplanting (DAT), out of 427 plants of cross I screened for GM resistance, 318 plants had nil gall incidence. In case of cross II, of the 798 plants screened, 557 plants had nil gall incidence. The male parent, RMSGM 3 was highly resistant (score 0) whereas the female parents, MTU1010 and MTU-IL 1 showed high susceptibility (score 9) and moderate resistance (score 3) respectively. The check TN1 had showed high susceptibility to GM (score 9) during this screening. The plants with GM resistance were subjected to molecular analysis using the resistance gene specific/linked markers i.e. the functional markers LRR-del for Gm4 gene, PRP for Gm8 gene, xa13 promoter for xa13 gene and tightly linked marker pTA248 for Xa21. Of the 318 F2 plants of cross I and 557 F2 plants of cross II, 254 and 332 plants respectively, were found to carry both Gm4 and Gm8 genes. Of these 84 and 238 plants respectively were homozygous for the resistant alleles of both GM resistance genes where as remaining were heterozygous for atleast one gene. Among these GM resistant plants which were also carrying the GM resistance genes, 112 plants of cross I and 101 plant of cross II that appeared phenotypically healthy, were screened with xa13 and Xa21 specific markers. In case of cross I, 36 F2 plants carried both xa13 and Xa21, 40 carried either xa13 or Xa21 and 36 plants were not carrying any BB resistance gene. But in case of cross II, all the 101 F2 plants carried both xa13 and Xa21 genes. Among these GM resistant plants carrying resistant alleles for three or four resistance genes, based on visual observations those which had medium or short height, with atleast eight effective tillers and which were early or on par with MTU 1010 in duration were selected based on visual observation, for forwarding to F3. Finally 59 plants of cross I (24 with four gene and 35 plants with three genes) and 55 plants (with four genes) of cross II were selected. During Rabi 2016-17, the selected F3 lines (progeny of selected F2 plants) along with parents and check (TN1) were raised. The lines were inoculated with hyper-virulent isolate (DX-066) of Xanthomonas oryzae pv. oryzae collected from ICAR-IIRR, Rajendranagar, at maximum tillering stage by using the leaf clipping method described by Kauffman et al. (1973). BB disease scoring was done 15 days after inoculation as per SES (IRRI, 2013). Data on parents and F3 lines were recorded when the susceptible check, TN1 shown complete susceptibility (score 9). MTU1010 also showed susceptibility with a score of 7. The male parent, RMSGM 3 as well as one of the female parent MTU-IL 1 showed resistance to BB with score of 1. Visual observation for BB reaction indicated that all the lines of both crosses to belonged to resistant class. Hence five best plants for each line were scored and these plants were also used for genotyping for presence of resistance genes. PCR analysis indicated that, in cross I, 46 lines were carrying Gm4 gene in homozygous condition and of these 44 lines were also carrying Gm8 in homozygous condition. Among these 44 lines, PCR with markers for BB resistance genes indicated that 26 lines were carrying both the BB resistance genes, 13 lines were carrying only xa13 and five lines were carrying only Xa21. Similarly, PCR analysis with plants from the 55 F3 lines of cross II, indicated 41 lines with Gm8 in homozygous condition and among these 41 lines also carried Gm4 in homozygous condition. These 41 lines were also carrying both the BB resistant genes in homozygous condition. These plants which carried three or four resistance genes (GM and BB) were observed visually and finally, 32 and 34 best F3 plants of cross I and of cross II respectively were selected for forwarding further. Data was recorded on agro-morphological traits for these selected plants along with parents. In conclusion, in this study reports early generation selection (F2 and F3) by combining molecular marker based screening for resistance genes along with field level selection for resistance as well as superior phenotype of plants. The F3 lines identified in this study could be forwarded and evaluated further. These lines hold potential for development of high yielding durable gall midge and bacterial blight resistant varieties in future which would be very useful for the farming community.EnglishThesis