ORIGIN AND SIGNIFICANCE OF CORN BELT MAIZE 



143 



nations were made and these tested for yield. In 1948, sixty-six single crosses 

 were grown in yield tests in Iowa and in Illinois. Each Fi hybrid was repli- 

 cated six times in each test. At the end of the season, yield of grain was de- 

 termined on the basis of 15 per cent moisture corn. Actual yields in bushels 

 per acre and morphological differences of the inbreds involved in each of the 

 crosses were then plotted on a scatter diagram as shown in Figure 8.6. It will 

 be noted that although the observations exhibit considerable scatter, there is 

 a tendency for grain yields in single crosses to increase as the morphological 

 differences between the inbreds making up the crosses become greater. 

 Actually the correlation coefficient between yield and index differences in 

 this case was r = +.39. 



The experiment was continued in 1949, in which 100 Fi hybrids were 

 tested for yield. In this experiment three characters only were used to deter- 



TABLE 8.2 

 INBRED INDICES BASED ON SEVEN CHARACTERS 



mine the index of relationship between the inbreds used. These were row 

 number, kernel length, and degree of development of husk leaf blades. 

 Elimination in this experiment of certain morphological characteristics used 

 previously was done largely to facilitate ease and speed of scoring. It had 

 been determined previously that, of the several characteristics used, those 

 having the highest correlation with yield were differences in row number, 

 kernel length, and husk leaf blades. There was likewise known to be a rather 

 strong association between each of these characteristics and tassel branch 

 number, denting, glume length, internode pattern, and chromosome knob 

 number. Therefore the scoring of these three characteristics probably covers 

 indirectly nearly as large a segment of the germ plasm as would scores based 

 on all seven characteristics. 



The 1949 tests in which each entry was replicated six times in each loca- 

 tion were again grown both in Iowa and Illinois. Yields from these tests, 

 plotted against index differences of the inbreds, are shown in Figure 8.7. 

 As in the previous year's data, a pronounced tendency was shown for hybrids 

 made up of inbreds of diverse morphology to produce higher grain yields than 

 hybrids consisting of morphologically similar inbreds. The correlation co- 



