Chromosomal Location of , a Broad-Spectrum Rice Bacterial Blight Resistant Gene from XM5, a Mutant Line from IR24.

Bacterial blight is an important rice disease caused by bacteria named pv. (). XM5 is an resistant mutant line with the genetic background of IR24, an Indica susceptible cultivar, induced by a chemical mutagen N-methyl-N-nitrosourea (MNU). XM5 carries a recessive resistant gene, . Trisomic analysis was conducted using the cross between XM5 and the trisomic series under the genetic background of IR24, showing that was located on chromosome 7. The approximate chromosomal location was found using 37 surely resistant plants in the F population from XM5 × Kinmaze, which was susceptible to most Japanese races. The IAS44 line carries a Japonica cultivar Asominori chromosomal segment covering the locus under the IR24 genetic background. Linkage analysis using the F population from the cross between XM5 and IAS44 revealed that was located within the 0.8 cM region between RM8262 and RM6728. is not allelic to the known resistant genes. However, its location suggests that it might be allelic to a lesion-mimic mutant gene , some alleles of which are resistant to several races. Together with and , three resistant genes were induced from IR24 by MNU. The significance of chemical mutagen as a source of resistance was discussed.