HYBRIDIZATION IN THE EVOLUTION OF MAIZE 195 



Data are available both from my experiments and those of R. G. Reeves 

 (1950), conducted independently, to indicate that heterozygosity for a block 

 of teosinte genes does sometimes confer a selective advantage. In 1944, in my 

 experiments, five Corn Belt inbred strains were crossed with the Texas in- 

 bred 4R-3, as well as with foar modified strains of 4R-3 in which teosinte 

 genes had been substituted for maize genes. The four modified strains may be 

 briefly described as follows: 



No. Blocks Teosinte 



Strain Genes Variety 



Modified 4R-3 Strain A 2 Florida 



Modified 4R-3 Strain B 2 Florida 



Modified 4R-3 Strain C 3 Durango 



Modified 4R-3 Strain D 3 Durango 



The Fi hybrids were grown in 1945 in two replications in a modified Latin- 

 Square yield test. Several hybrids were omitted for lack of sufficient seed. 

 The results are shown in Table 11.4. 



TABLE 11.4 



AVERAGE YIELDS IN BUSHELS PER ACRE OF HYBRIDS OF 



CORN BELT INBREDS WITH TEXAS 4R-3 AND ITS 



TEOSINTE-MODIFIED DERIVATIVES 



* Difference probably significant. 



Of the 17 hybrids tested, only 3 proved to be better than the correspond- 

 ing checks in total yield, and in only 2 of these is the difference significant. 

 Although the data are not extensive, there is some indication that the Corn 

 Belt inbred strains used in these experiments differ in their ability to "com- 

 bine" with the teosinte derivatives. 



Perhaps more important than total yield, from the standpoint of selective 

 reproductive advantage, is total number of seeds per plant (Table 11.5). 

 Here 6 of the 15 hybrids for which data are available were superior to the 

 checks, 4 of these significantly so. 



These results, so far as they go, are in agreement with the recently pub- 

 lished results of Reeves (1950). Reeves tested 49 modified 4R-3 lines in hy- 

 brids with a common tester. He found none significantly better than the 

 check in yield, although several were superior in heat-tolerance. Reeves 



