188 MUTATION AND PLANT BREEDING 



apparently dominant for either Ma 2 or Ma 3 or both. YelloAV milo 

 (60-day) is genetically Ma^ ma 2 ma 3 . Hybrids of 60-day Milo and 

 Texas Blackhull Kafir, Hegari, Early Hegari, and California White 

 Durra are extremely late in maturity. Hybrids of 60-day Milo and 

 Early Kalo, Kalo, Bonar Durra, Feterita F. C. 81 1, Manko, and Fargo 

 are later in maturity than either parent but not extremely late. The 

 latter group is probably dominant for either Ma 2 or Ma 3 and the 

 former for both Ma 2 and M« 3 . Obviously, more than three major 

 maturity genes may exist in sorghum and all the milos might be 

 dominant for a fourth gene. The late-maturing kafir introduced into 

 the United States in 1880, since it was so late in maturing, must have 

 been dominant for all three genes. If Blackhull Kafir came from this 

 late-maturing kafir, it arose as a recessive mutation at the AlY/i locus. 

 Several varieties are sensitive to photoperiod at the tempera- 

 tures that prevail in the summer months at Chillicothe, Texas, but 

 many other varieties are insensitive or show varying degrees of 

 sensitivity. Data in Table 2, taken from Quinby and Karper (26), 

 show the response of 12 varieties to photoperiod at Chillicothe, 



Table 2. — Effect of 10-hour Photoperiod on Time of Floral Initiation, Leaf 

 Number, and Time of Anthesis of Sorghum Varieties Planted July 13, 1941, 



at Chillicothe, Texas. 



Number of days from planting to 



•Short day exposure to sunlight was 10 hours. In July at Chillicothe, Texas, the sun is above 

 horizon for about 14 hours. 



