DEVELOPMENT OF PRE-ISOGENIC LINES FOR RICE BLAST RESISTANCE BY MARKER-AIDED SELECTION FROM A RECOMBINANT INBRED POPULATION

To increase the available set of near-isogenic lines (NILs) for blast- resistance in rice: we have developed a general method for establishin g NILs from populations of fixed recombinants that have been used for gene mapping. We demonstrated the application of this method by the se lection of lines carrying genes from the rice cultivar Moroberekan. Mo roberekan is a West African japonica cultivar that is considered to ha ve durable resistance to rice blast. Multiple genes from Moroberekan c onferring complete and partial resistance to blast have previously bee n mapped using a recombinant inbred (RI) population derived from a cro ss between Moroberekan and the highly and broadly susceptible indica c ultivar CO39. To analyze individual blast-resistance genes, it is desi rable to transfer them individually into a susceptible genetic backgro und. This RI population, and the associated data sets on blast react-i on and restriction fragment length polymorphism (RFLP) genotypes, were used for selection of lines likely to carry individual blast-resistan ce genes and a minimum number of chromosomal segments from Moroberekan . Because skewed segregation in the RI population favored CO39 (indica ) alleles, resistant lines carrying 8.7-17.5% of Moroberekan alleles ( the proportion expected after two or three backcrosses) could be selec ted. We chose three RI lines carrying different complete resistance ge nes to blast and two RI lines carrying partial resistance genes to bla st as potential parents for the development of NILs. These lines were subjected to genetic analysis, which allowed clarification of some iss ues that could not be resolved during the initial gene-mapping study.