330 



GENETICS IN RELATION TO AGRICULTURE 



An interesting illustration of what can be accomplished in maize 

 merely by mass selection, when a definite ideal is maintained and seed 

 is selected in the field before harvesting, is found in the Delta Farm White 

 Corn shown in Fig. 136. 



Selection Methods in Breeding Close -pollinated Plants. The suc- 

 cessful methods of breeding wheat have been reviewed in preceding 

 chapters. Compared with the methods required for corn the work of 

 isolating genotypes in wheat is relatively simple. Most commercial 



2 



FIG. 137. Typical heads from seven pure lines of Defiance wheat. Nos. 1 and 2 do 

 not yield one grain per spikelet on the average; Nos. 6 and 7 yield from 4 to 7 grains per 

 spikelet. Note tendency to club type in No. 6. 



varieties of wheat are a mixture of pure lines which can be isolated by 

 single plant selections. In Fig. 137 is shown a typical head from each 

 of 7 different pure lines isolated by selecting single plants from a plot of 

 Defiance wheat. Nos. 1 and 2 did not have an average of one grain 

 per spikelet while Nos. 6 and 7 bore from 4 to 7 grains per spikelet. If 

 Nos. 6 and 7 prove to be superior in other characters also, they need only 

 to be multiplied in order to yield greatly improved strains of the Defiance 

 variety. It was by this method that Roberts in 1906 isolated a pura 

 line of Turkey wheat that appears very promising for the Great Plains 

 Region. It is worthy of note that this superior pure line was the 135th 



