186 MUTATION AND PLANT BREEDING 



but a few alleles resulted from mutations after sorghum was intro- 

 duced about 100 years ago. All of the alleles must have arisen as 

 spontaneous mutations originally and no effort will be made to 

 distinguish between recent and ancient mutations. 



Nevertheless, eight mutations have occurred in milo and have 

 been preserved during 80 years in the United States. Four of these 

 eight that control response to photoperiod occurred at three 

 loci. Two were alleles that reduce height, one affects pericarp color, 

 and one causes resistance to a root-rotting fungus. The Y gene that 

 causes colored pericarp mutated to recessive y in milo before 1910 

 and White Milo resulted. The recessive mutation causing resistance 

 to periconia root-rot must have occurred many times because a few 

 resistant plants could be found in almost any badly diseased field 

 of any of several milo varieties when the disease first became seri- 

 ous. Probably mutations at some loci occur again and again. Con- 

 versely, many other genes have not been seen to mutate in the 50 

 years that sorghum has been worked with by plant breeders in the 

 United States. For instance, the yellow endosperm character was 

 never seen in the United States until O. J. Webster returned with it 

 from Africa in 1951. 



Maturity Genes 



The history and evaluation of milo in the United States has 

 been presented by Karper and Quinby (13, 14) and by Vinall, et al. 

 (43). Another early-maturity genotype has appeared in more recent 

 years. When "Millo Maize" reached the United States in 1879 it 

 was a tall, late-maturing variety. When tested at the Louisiana 

 and Kansas Experiment Stations in 1888, the variety matured in 

 about 120 days, indicating a time of blooming about 90 days from 

 planting. By 1900, the variety in use in western Texas was Standard 

 Milo that bloomed in about 65 days and matured in 95 days. Before 

 1910, farmers in western Texas were growing Early White Milo 

 that bloomed in 50 days and matured in 80 days. In 1938, a farm- 

 er in California found a still earlier maturing milo that bloomed 

 in 44 days and matured in 75 days. Commercial production of this 

 early-maturing milo, called Ryer Milo, began about 1948. 



The inheritance of duration of growth in milo has been reported 

 by Quinby and Karper (25, 29). Three genes influence plant 

 response to photoperiod and control the time of floral initiation. 



