Screening and Molecular Characterisation Of Near- Isogenic Lines for Resistance to Rice Yellow Mottle Virus

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JUNE, 2010
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Rice yellow mottle virus is a serious disease affecting rice production in the lowland and irrigated ecologies. This study was conducted at the Africa Rice Center, Cotonou, Benin. An Augmented design with 2 replicates and control was used. Several near isogenic lines with rymv1-2 resistant allele were developed by the Biotechnology Unit of Africa Rice Center and evaluated in the field for their resistance to RYMV in the Republics of Mali and Guinea. the study examined 100 near isogenic lines from BC2 F7 population, 7 parental lines and 3 checks were screened for RYMV resistance. The cross combinations were derived from Gigante x IR64, Gigante x FK28 and Gigante x IR47. Results from phenotypic screening identified 20 NILs to be resistance to RYMV B27 isolate. Enzyme Linked-immunosorbent assay (ELISA) test revealed 36 to be resistance to RYMV with low virus content. Polymorphism test revealed an average of 71% of the SSR markers used across the rice chromosomes showed polymorphism among couple of parental lines. Foreground selection using the gene marker RM252 revealed 22 of the lines showed introgression of rymv1-2 allele and the rest do not show the resistant gene. The proportion of each parent was examined using the polymorphic makers between parental lines. The proportion of recurrent parent allele IR64 was 57% whereas the proportion of the donor parent allele Gigante was 34% and non-parental allele was 9%. The individual from Gigante x FK28, has 19% of the recurrent parent, 70% of donor parent, 9% of non-parental allele and 2% heterozygote. The individual from Gigante x IR47, has 17% of the recurrent parent, 71% of the donor parent, 10% of non-parental allele and 2% heterozygote. Comparing the genomic proportion among individuals, the individual from Gigante x Fk28 has the highest percentage of the donor parent whereas the individual from Gigante x IR64 has the lowest percentage of the donor parent but showed the highest genomic proportion of the recurrent parent. Since the management of rice yellow mottle virus using cultural practices help to reduce the impact of RYMV, the use of resistant varieties gives sustainable way. The integration of of screen house experiments together with marker-assisted selection would be more efficient and durable for the poor resource farmer.
A Thesis Submitted to the Board of Postgraduate Studies, Kwame Nkrumah University of Science and Technology, Kumasi in Partial Fulfilment of the Requirement for the MASTER OF SCIENCE DEGREE in PLANT BREEDING,