Abstract
To increase the genetic resources for resistance to bacterial blight (BB) caused by Xanthomonas campestris pv, oryzae in rice, we initiated a study to induce mutants with resistance to BB by chemical mutagen. Fertilized eggs of a susceptible cultivar, IR24 to Philippine BB races were treated with N-methyl-N-nitrosourea (MNU) at the singie-cell stage of embryogenesis. The panicles of F1 plants were bagged before flowering to avoid any outcrossing. M2 lines, derived from each M1 plant, were inoculated with a Philippine BB race 5 (isolate PXO 112) at the seedling stage. As a result, out of 2, 739 M2 lines tested, two resistant mutant lines were found and they were designated XM5 and XM6. M3 progenies derived from M2 plants in both mutant lines were tested for segregation for resistance. The results suggested that resistance of these mutant lines was induced by the MNU treatment. The mutation frequency of BB resistance was 7.30 × 10-4. (no. of resistant mutant lines/no. of tested M2 lines). Both of the mutant lines showed resistant to all six known Philippine BB races. We crossed these two resistant mutant lines with IR24 to clarify their inheritance of resistance. The reaction of F1 hybrids and F2 populations to BB races suggested that both mutant lines have single recessive genes for BB resistance.
