Allelic Relationships and Inheritance of Brown Midrib Trait in Sorghum

Four naturally occurring brown midrib mutants in sorghum identified in 1989 in germplasm from Malawi and 3 brown midrib lines previously developed at Purdue University, Indiana, USA through induced mutations (bmr-6, bmr-12 and bmr-18) were considered in this study. Allelism tests in these 7 lines revealed that the 4 naturally occurring brown midrib lines were allelic to each other and to bmr-6. These 5 lines were non-allelic to bmr-12 and bmr-18, whereas bmr-12 and bmr-18 were allelic to at least those genes necessary to express the brown midrib trait. Inheritance of the trait in F1 and F2 populations derived from 15 crosses between 9 normal midrib parents and 3 brown midrib lines was then studied. Results revealed that the brown midrib trait is controlled, at least in part, by genes at 2 or more independent loci in the nuclear genome of sorghum. There is a strong possibility that some modifying genes may affect the expression of this trait. In general, 15-45% of plants with brown midrib can be expected in F2 populations segregating for this character