The inheritance of three genes that influence time of floral initiation and maturity date in milo

A study of the inheritance of duration of growth in milo, a grain sorghum group, disclosed that four maturity phenotypes exist that are the result of the action of three genes. Lateness is dominant to earliness, but the second and third genes, Ma2 and Ma3, do not express themselves except in the presence of dominant Ma. Also, the third gene, Ma3, does not express itself in the presence of dominant Ma2, and on account of these conditions four phenotypes represent all eight genotypes. The four phenotypes for maturity have been designated as Early, Intermediate, Late, and Ultra-late. The gene Ma was found to be linked with Dw2, a gene that influences length of internode. The gene Ma3 was found to be linked with R, a gene that controls presence or absence of a plant pigment. The action of the gene Ma is influenced by photoperiod. When grown under 10-hour photoperiods, the Early, Intermediate, Late, and Ultra-late genotypes of the 14-hour photoperiod were identical in appearance. The genes Ma2 and Ma3 were not able to express themselves if the plants were grown under 10-hour photoperiods and not under 14-hour photoperiods unless the gene Ma was present in the dominant condition. Three types of internodal disposition occurred among the four phenotypes for maturity. The Early strain had internodes that increase in length from the ground to the peduncle. The Intermediate strain had a short internode near the top of the plant with longer internodes above and below it. The Late and Ultra-late strains had two areas of constriction, one close to the ground and the other close to the top of the plant. This study of the inheritance of duration of growth in milo is actually concerned with the time of floral initiation. The time of floral initiation controlled the number of leaves, the duration of growth, and the ultimate size of plant. A difference in two genes that influenced duration of growth was sufficient to bring about a two-fold difference in plant size. The three genes found to affect maturity date in milo are typical adaptation genes and they determine the range in both latitude and altitude as well as the rainfall belt in which a strain or variety can be grown successfully as a grain crop. This study leads to the belief that adaptation and normal growth are under control of fewer genes than is generally supposed. Varietal adaptation is explained by these results as well as unequal response of a single variety to different environments. An understanding of the inheritance of these genes and the manifestations produced by them is valuable in a program of crop improvement.