Inheritance of resistance to spot blotch disease in wheat.

The mode of inheritance to spot blotch or Helminthosporium leaf blight (HLB) resistance was studied in segregating populations of 15 crosses involving two resistant wheat lines; a Thinopyrum derived CIMMYT wheat line, CIGM 84-295-1, and a Chinese line, Ning 8201. The disease reaction of F1 and F2 progeny of crosses involving the resistant wheat line, CIGM 84-295-1 and four susceptible lines indicated monogenic recessive resistance to HLB, whereas crosses involving Ning 8201 with the same susceptible parents showed resistance was controlled by a dominant gene. The segregation ratio of F2 progeny derived from the cross, Ning 8201 x CIGM 84-295-1 (resistant x resistant) followed a ratio of 13 resistant: 3 susceptible as expected for genetically two independent dominant and recessive genes. The F3 progeny testing of the F2 susceptible plants confirmed the presence of dominant and recessive gene interaction. The progeny obtained from the crosses between the susceptible parents were all susceptible to HLB disease.