Bacterial leaf blight (BLB) disease is an emerging issue in rice cultivation of Sri Lanka. Xanthomonas oryzae pv. oryzae is causal organism. There is no chemical control method practice in the world to control the disease. Use of resistance varieties is most appropriate mode of control. Bacterial blight resistance Xa21 and Xa4 are dominant genes responsible for durable resistance of rice varieties for the disease. The advanced rice line, Ld 99-12-38 is farmer demanding, non lodging type, high yielding rice line and is susceptible to BLB. Therefore, an attempt was taken to improve it resistant to BLB through markerassisted backcross breeding (MAB) by crossing rice line with resistant variety IRBB60, and advanced plants up to BC 3 F 2 level. At the beginning selected two molecular markers namely pTA248 (Xa21) and PM1+MP2 (Xa4) were tested for their polymorphism with parental materials. To identify BLB resistance Xa21 and Xa4 alleles, markers were validated in thirty five BC 3 F 2 progenies derived from a cross between Ld 99-12-38/IRBB60. As the results selected two molecular markers were polymorphic with parental materials with the expected fragment sizes. Out of the tested 35 progenies, eight were confirmed with possessing both Xa21 and Xa4 with resistant to the disease, twenty one lines carried only the resistant allele Xa4. A paired t-test revealed that there is a significant difference in the resistance level exerted by progeny carrying resistance alleles of two genes than with one (p = 0.0064). In addition, six progeny lines were heterozygote for Xa4 locus; one progeny line was heterozygous at both loci. No lines were identified carrying only the Xa21. Therefore it can be concluded that resistant genes Xa4 and Xa21 has been pyramided to rice lines derived from cross between Ld 99-12-38/IRBB60 in BC 3 F 2 progenies with similar morphological characters of Ld 99-12-38 to withstand BLB. The rice line Ld 99-12-38 does not carry any resistance genes regarding BLB and IRBB 60 consist of Xa21 and Xa4 alleles. The selected markers pTA248 and MP1+MP2 can be recommended to in marker-assisted selection of Xa21 and Xa4 genes in crosses involving the tested genetic background.
the development of rice cultivars with desirable traits is essential. the decision-making is a crucial step in rice breeding programs. Breeders can make efficient and pragmatic decisions if an organized pedigree visualization platform is available for the accessions and cultivars in rice breeding germplasm. in the present study, the available data of all the rice varieties released by Rice Research and Development institute, Sri Lanka, and the related landraces and genotypes were arranged in pedimap, a pedigree visualization tool. pedimap can showcase pedigree relationships, phenotypic, and molecular data. the identity by descent probabilities were calculated using flexQtL software and included in the pedimap database. the parentage selection based on the variations of phenotypic traits, selection of marker alleles for molecular breeding, and detection of the founders of genetic effects can be swiftly conducted using Pedimap. However, the power of harnessing the value of pedimap for making breeding decisions relies on the availability of data for the traits, markers, and genomic sequences. thus, it is imperative to characterize the breeding germplasms using standard phenomic and genomic characterization procedures such as the assessment of before organized into Pedimap. Thereby, the worldwide breeding programs can benefit from each other to produce improved varieties to meet global challenges. Rice is one of the major crops in the world, with an annual production over 700 million metric tons 1. Half of the world population consumes rice as the staple food 2. Currently, the demand for rice is rapidly increasing due to the growth of the human population 3. However, the current rice production cannot meet the increasing demand causing severe food security issues. The biotic and abiotic stresses also exert a negative influence on rice production 4. The rice farming is also a way of living for many people, especially in numerous Asian countries 5. At present, 1.8 million Sri Lankan families engage in rice farming over 870,000 hectares 6. The annual rice production in Sri Lanka is approximately 2.3 million metric tons (MT), which is insufficient to fulfill the domestic rice demand of 3.0 million 7. Hence, the Sri Lankan government spends about USD 400 million to import rice annually 7,8. The rice production is mainly affected by drought and irregular rainfall patterns caused by climate change 9-11 , adverse soil conditions such as salinity 6,12 , and pest and disease attacks 13. The biotic and abiotic stresses in rice farming can be controlled using numerous agronomic practices such as irrigation, drainage, fertilization, and the application of pesticides. However, the rate of success of the controlling methods is limited 13 due to the unpredictable nature of climate change, soil degradation, variations in pest dynamics, and development of pest resistance 14. Therefore, breeding is considered as the most successful strategy to produce high yielding and stress-resilient rice varieties 15. The improved rice genotypes can...
Sustainability of transplanting systems for rice crop establishment in Sri
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