QUINBV! MUTATIONS IN SORGHUMS 



187 



The genes have been named Ma 1} Ma 2 , and Ma 3 . Only one recessive 

 allele is known at each of the M«i and Ma 2 loci, but two recessive 

 alleles are known at the Ma 3 locus. Recessive ma^ and ma\ act 

 like amorphic alleles since they cause early floral initiation when 

 homozygous. Recessive ma 2 and ma 3 modify the expression of the 

 dominants and are not amorphic. The various milo maturity geno- 

 types (but not the infrequent cross-over genotypes) that emerge 

 from crosses of Early White Milo with Yellow Milo and with 

 Ryer Milo are shown in Table 1. The "Millo Maize" introduced 



Table 1. — Milo Maturity and Pericarp Color Genotypes and Phenotypes, 

 Excluding Crossover Classes, at Chillicothe, Texas, from 

 Early June Plantings. 



Genotype 



Mai Ma 2 (Mazy) 



A/ai Mai (mazY) 



Mai Ma-2 (ma n 3 Y) 



Mai mai (Mazy) 



mai Ma-i (Ma 3 y) 



Mai mai (ma 3 Y) 



Mai ma* {ma zY) 



mai Ma-i (ma 3 Y) 



mai Ma 2 (ffw R jf) 



mai mai (Mazy) 



mai mat (mazY) 



mai mai (ma zY) 



Days to bloom Pericarp color 



in 1879 was evidently dominant for all three maturity genes and 

 has been reconstituted by selecting the late-maturing genotype 

 from the F 2 generation of appropriate crosses. A genetic linkage 

 exists between the white pericarp color gene y and Ma 3 and between 

 the maturity gene Mai and the dwarfing gene dw 2 . 



Of the many varieties grown in the United States and tested 

 for photoperiod response, only Yellow Milo (60-day), Hegari, and 

 Early Hegari, and a few of their derivatives, are dominant Ma x . The 

 remainder, including the parents of the present sorghum hybrids, 

 are recessive max and have a critical photoperiod high enough to 

 allow relatively early floral initiation and maturity. The dominant 

 or recessive condition of the genes at the Ma 2 and Ma z loci is 

 unknown for most varieties other than the milos, but most are 



