The Question of Colchicine Induced Somatic Reduction and the Production of Homozygous Diploid Mutants in Sorghum

Abstract

Franzke and Ross (1952) reported that colchicine treatment of sorghum resulted in the production of mutants which bred true. Over the past ten years these authors and their associates have published many articles on this subject. These reports have aroused considerable interest and caused puzzlement among investigators in cytogenetics. Recently Sanders and Franzke (1962) in summary comment about the overall experiments with sorghum state as follows: Colchicine treatment of seedlings of lines has resulted not only in the expected polyploids, but also in diploid plants which are mutant for many characters. Some of these diploid mutants breed true immediately while others give segregating progenies. They point out that the unique results were obtained with only certain sorghum lines, derived from the Experimental 3, which was of complex hybrid origin (Franzke and Ross, 1952). Also it appears that results with these sorghum lines were obtained only when seedlings were cultured in specially devised environment (Sanders and Franzke, 1962). Sanders and Franzke (1962) reported obtaining diploid plants by treating tetraploid seedlings. As in earlier experiments with sorghum, they applied colchicine, 0.5 per cent in lanolin, by coating the coleoptile of germinating seeds. In this experiment nine of 20 seedlings survived. Meiotic examination showed four to be diploid, one to be a mixoploid made up of cells with diploid and different polyploid numbers, and four to be tetraploid. Cytological examination of large number of plants from untreated seedlings showed all to be tetraploid. Therefore, the authors concluded: The possibility of diploids being present originally in this tetraploid population would appear to be ruled out. Earlier publications of Franzke and co-workers on sorghum were concerned mainly with the production of homozygous diploid mutants obtained from colchicine-treated diploid seedlings. Sanders and Franzke (1962) found in the recent experiment very high percentage, over 40 per cent to be exact, of haploid plants (tetraploidy reduced to diploidy) after treatment of tetraploid seedlings. To account for these results the following assumptions would have to be made: