191 



MUTATION AND PLANT BREEDING 



influence of dwarfing genes on leaf sheath, peduncle length, and 

 head length are shown in Table 6. Kafir plants of these height geno- 

 types giowing together at Chillicothe, Texas, in 1960 were tagged 



Table 6. — Days from Planting to Blooming and Size of Various Plant Parts of 

 Three Height Genotypes of Kafir at Chillicothe, Texas, in 1960. 



Criteria 



2-dwarf 



Height genotype 



3-dwarf 



4-dwarf 



Days from planting to blooming; 55.5 ± 0.6 55.6 ± 0.4 56.8 ± 0.4 



Flag leaf sheath length, cm 33.4 ± 0.4 32.5 ± 0.6 30.6 ± 0.4 



Height to upper node, cm 79.4 ± 1.0 34.2 ± 0.5 20.9 ± 0.5 



Peduncle length, cm 32.5 ± 0.9 31.7 ± 0.8 35.6 ± 0.8 



Head length, cm 20.2 ± 0.4 23.1 ± 0.4 21.6 ± 0.3 



Total height, cm 132.2 ± 1.3 89.0 ± 1.1 78.1 ± 1.0 



Stalk diameter, cm 1.65 ± 0.04 1.83 ± 0.03 1.58 ± 0.04 



for days from planting to blooming and were measured for height 

 from the base of the culm to the upper node for peduncle length, 

 head length, and flag leaf sheath length. The 2- and 3-dwarf classes 

 were isogenic lines, but the 4-dwarf class was a derived line that 

 was similar in maturity but not isogenic with the other two. The 

 data show that even the 4-dwarf genotype has a peduncle and head 

 as long as those of taller 3-dwarf and 2-dwarf genotypes. 



Rapid internode elongation in sorghum follows floral initia- 

 tion, indicating some connection between the presence of a floral 

 bud and internode elongation. The mechanism involved in the 

 shortening of the internodes without a shortening of the peduncle 

 and head is as yet unknown. Far-red radiation is now known to induce 

 floral initiation and influence internode elongation (8). Probably 

 dwarfing genes in sorghum slow down the synthesis of the sub- 

 stance that causes elongation. 



Genes For Resistance to Disease and Insects 



The diseases of sorghum and the organisms that cause them 

 have been described by Leukel, et al. (19). Resistance to some of the 

 diseases is present in one or more varieties and resistance to some 

 diseases has been bred into some varieties. 



All of the different strains of milo grown on farms in the United 

 States prior to 1937 were susceptible to milo disease, later identified 



