Abstract
Sanders, Mary E., Clifford J. Franzke, and James G. Ross. (South Dakota State Coll., Brookings.) Influence of environmental factors on origin of colchicine‐induced true‐breeding diploid mutants in sorghum. Amer. Jour. Bot. 46(2) : 119‐125. Illus. 1959.—Factors involved in the induction of true‐breeding diploid mutants following colchicine treatment of sorghum seedlings (line ‘Experimental 3‘) were studied by growing untreated and treated seedlings in aseptic cultures under controlled conditions and examining mature plants and progenies for genetic changes. Factors found to increase rate of early growth and survival of treated seedlings are: use of agar media rather than quartz sand plus liquid media, presence of major minerals in the medium, and presence of up to 2% sucrose in the medium. The beneficial effect of sucrose is contingent upon the presence of major minerals. IAA from 0.01 p.p.m. to 0.1 p.p.m. increased rate of both root and top growth of treated seedlings during early development. Increased osmotic values of the medium increased early growth rate and survival of treated seedlings up to a concentration equivalent to 0.123 molar sucrose while early growth of control seedlings fell off with every increase in osmotic value. This shift in optimum osmotic value of the medium would seem to indicate an increase in the osmotic concentration of the tissues of colchicine‐treated seedlings. Progeny tests of some of the treated plants from the culture experiments demonstrated that, out of 137, none were true‐breeding diploid mutants. There were instances of polyploidy and minor changes, but the 2 treated plants which were the only obvious mutants gave progenies which segregated for many characters. Improved growing conditions for treated seedlings decreased the colchicine effect of induction of true‐breeding diploid mutants as well as the colchicine effects of retarded seedling growth and decreased survival.
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