EARLY TESTING AND RECURRENT SELECTION 



409 



substitute for the more refined tests possible when the lines are more nearly 

 homozygous. This limitation was clearly outlined in the 1946 paper (Sprague, 

 1946). 



Data have also been presented by Singleton and Nelson (1945) which 

 they interpret as demonstrating the inefifectiveness of early testing. In the 

 stud}' reported, forty-eight ears were chosen from the variety Whipple early 

 yellow. These were grown ear-to-row and one self made within each lot. The 

 selfed plants were also outcrossed to the inbred line P39. Selfing was continued 

 for three generations. In each generation the plants chosen for selfing were 

 outcrossed to P39. At the end of this period of selfing and testing, ten lines 

 were chosen for this special study. By using remnant seed, test crosses were 



TABLE 26.4 



ANALYSIS OF VARIANCE FOR YIELD. 1940 AND 1941 

 (AFTER SINGLETON AND NELSON, 1945) 



produced involving So, Si, S2, and S3 generations. No data are given in the 

 publication but an analysis of variance for the two-year test period is pre- 

 sented in Table 26.4. 



At least two points concerning the analysis are worthy of mention. First 

 there were no significant differences among the ten lines studied. In view of 

 the extensive testing back of the group of lines chosen, and because they \\ere 

 selected to be very similar in yield, it is not surprising that the early testing 

 procedure failed to disclose differences. The early testing procedure is cer- 

 tainly not suited to the measurement of very small differences. However the 

 degree of genetic uniformity with respect to combining ability would normal- 

 ly not be expected in sampling with open-pollinated or Fo populations. 



The second comment bears on their interpretation of improvement in 

 combining ability during the course of inbreeding. The appropriate test of 

 significance in this case depends upon the specific question the data are 

 asked to answer. If conclusions are to be confined to the particular lines used, 



