GAMETE SELECTION FOR SPECIFIC COMBINING ABILITY 387 



from crosses of inbreds may be more restricted than their inbred parents in 

 commercial use because of relationship. It seems probable to the writers that 

 the method of gamete selection is worthy of considerable use for further 

 selection of material from open-pollinated, desirable commercial varieties. 

 Studies of lines recovered from selected varietal gametes will have to be 

 carried to F5 or later generations to determine if the large amount of out- 

 cross testing is justified economically. The writers would like to emphasize 

 the importance they attach to method studies of the type presented here. 

 New ideas in breeding must be explored constantly if continued progress is 

 to be made in corn improvement. 



SUMMARY 



Since 1945, a program has been underway at Minnesota to attempt im- 

 provement of Minhybrids 602, 607, and 406 by the method of gamete selec- 

 tion. The hybrid pedigrees are respectively: (A344XA334) (A357XA392), 

 (A344XA334) (A357XA385), and (A25XA334) (A73XA375). Detailed 

 studies of the non-parental single crosses among the inbred parents of each 

 hybrid led to the conclusion that A344 in Minhybrids 602 and 607, and A25 

 and A73 in Minhybrid 406 were low in combining ability. 



A344 was crossed to the Morris strain of Minnesota 13 and to eight in- 

 breds of diverse origin. A25 was crossed to the Golden King variety and A73 

 to Murdock. (Inbred X gamete) (tester) crosses were made using the oppos- 

 ing single cross parents as testers. These were compared with the appro- 

 priate cross of inbred X tester. Yield trial performance was obtained from a 

 total of 113 gametes, 35 from Morris 13, 8 inbreds, 32 from Golden King, 

 and 38 from Murdock. 



Sixteen gametes from Morris 13, three from the inbreds, and eight from 

 Murdock gave significant increases in yield over the test crosses of the checks 

 A344 and A73. Five gametes from Morris 13, eight from Golden King, and 

 fourteen from Murdock were not significantly different in yield but were 

 significantly earlier so that yield performance could be considered better 

 than the checks on the basis of ear moisture at harvest. These varieties and 

 the three high testing inbreds thus appear to be good sources of gametes for 

 improving the relatively low performing inbreds in specific combining ability 

 for yield. 



Both high and low testing varietal gametes were selected for use in a study 

 of the development of new inbreds. From the crosses, A25X Golden King and 

 A73X Murdock, selected F2 plants X the approj)riate tester were compared 

 with the progeny of their Fi parental plants when crossed on the same tester. 

 While there was excellent agreement, on the average, for combining ability 

 in the Fi and F2, there was evidence of segregation for combining ability from 

 almost all of the twelve Fo families which were studied. Visual plant selection 

 within the F2 generations appeared to be effective in increasing yield per- 



