DEVELOPMENT OF THE HETEROSIS CONCEPT 



53 



Powers (1945) obtained also relatively good agreement in tomatoes be- 

 tween the parental yield of 10 varieties and that of all possible Fi crosses 

 between the 10 varieties (see Table 3.3). 



Moore and Currence (1950) in tomatoes made a somewhat comparable 

 study to that of Carnahan with flax. They used two three-way crosses as 

 testers for a preliminary evaluation of combining ability of 27 varieties. 

 Based on this, eight varieties were selected that gave a wide range in aver- 

 age combining ability for sev^eral characters including early yield and total 

 yield. These varieties were crossed in all combinations, and yield trials of the 



TABLE 3J 



YIELD OF RIPE FRUIT IN GRAMS 

 IN TOMATOES (AFTER POWERS) 



varieties and Fi crosses were made. There was relatively good agreement 

 between the early test for combining ability and the average yield of Fi 

 crosses, but the relationship did not seem superior to the varietal performance 

 as a means of predicting combining ability in crosses. In the studies by Carna- 

 han, Moore, Currence, and Powers the only means of selecting the most de- 

 sirable Fi cross was by actual trial. 



Characters of inbred Lines and Their Fi Crosses in Maize 



Numerous studies have been made with maize of the relation between 

 characters of inbred lines and of their Fi crosses. There usually have been 

 indications of significant correlations for most characters of inbred lines and 

 their Fi crosses. In most cases, however, the relationship was not very large 

 or highly important when one studied individual characters, or the more com- 

 plex character — yield of grain. The studies have been reviewed by numerous 

 workers (see Sprague, 1946b). 



