382 E. L. PINNELL, E. H. RINKE, AND H. K. HAYES 



are considered superior in yield performance on the basis of maturity. Eight 

 gametes from Murdock demonstrated yield potential greater than A73, as 

 indicated by significantly higher yields in crosses. In addition, fourteen 

 gametes not different from A73 in yield were significantly earlier in maturity. 

 The proportion of promising gametes extracted from the three varieties 

 and the eight inbreds is summarized in Table 24.8. About 25 per cent of the 

 total number tested were superior to the sampler inbred in yield potential. 

 Another 25 per cent would be considered desirable parents because they had 

 a yield potential equal to and a maturity potential which was significantly 

 earlier than the sampler inbreds. 



SELECTION OF GAMETES AS PARENTS AND TESTS 

 OF F2 PROGENIES 



Years of testing at Minnesota have led to the conclusion that, in general, 

 there is a direct relation between yield and moisture content at husking 

 among hybrids of equal genetic desirability. On this basis the combining 

 ability of inbred X gamete plants was determined by considering both yield 

 and moisture percentage at husking. They were effectively placed on a com- 

 parable basis by calculation of a performance index using the test cross of 

 the sampler inbred as 100 for both ear moisture and yield. For example, if 

 the moisture percentage of an A25 X Golden King plant (in test cross) was 

 93.5 as compared with A25 X tester, and its yield was 106.5 per cent, its per- 

 formance index would be -f 13. Where the comparative moisture percentage 

 is higher than the yield percentage the index becomes a negative value. 



The performance indices for the selected gametes for both 1947 and 1949 

 trials and similar data for the F2 plant progeny tests appear in Tables 24.9 

 and 24.10. The tests of F2 plants from gametes of both high and low yield 

 potential were made as explained in "Materials and Methods". This wa scar- 

 riedout by selfing selected F2 plants and also crossing them with the appro- 

 priate tester, and again comparing the results with the crosses of the appro- 

 priate inbred with the same tester. Agreement between the two tests of the 

 gametes was very good except for Murdock gametes numbered 12 and 49. 



On the average there was good agreement between Fi and F2 progeny 

 performance. Tables 24.11 and 24.12 show that there is evidence of segrega- 

 tion for yield factors within almost all of the F2 families tested. 



Mean performance of the F2 progeny from the high testing gametes was 

 little different from the Fi for either ear moisture or yield (Table 24.13). 

 However, the F2 progeny from the gametes of low yield performance ex- 

 ceeded the Fi parent plant in yield performance on the average. This indi- 

 cates that visual selection of plants within the F2 populations was more 

 effective among the progenies arising from the gametes of low yield per- 

 formance than for those F2 plants that were selected from high performing Fi 

 crosses (gamete X inbred). 



