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



DISCUSSION 



Almost 50 per cent of the gametes studied showed evidence of having 

 combining ability in excess of the sampler lines. The gametes chosen as par- 

 ents appear to furnish a desirable source of germ plasm for a selection pro- 

 gram designed to improve the yield potential of A344, A25, and A73 in 

 combining ability in specific crosses. 



Where a high combining varietal gamete is chosen for an inbred selection 

 program, the Fi plant of which it is a parent represents a high X low type of 

 cross so far as combining ability is concerned. To the extent that such Fi 

 plants are comparable to crosses of inbreds, the breeding results should be 

 similar to those from crosses of inbreds differing in combining ability. At 

 Minnesota (Hayes and Johnson, 1939), crosses of highXlow combiners have 

 given F5 lines ranging from high to low, but with a good proportion of high 



combiners. 



Whether selection of gametes should be followed by test controlled selec- 

 tion in the F2 is an important question. In these studies more than 50 per 

 cent of the F2 plants from high combining gametes tested at least ten per- 

 formance index units higher than the sampler inbred. Thus without further 

 test crosses, the chances of choosing high combining F2 plants would still 

 have been very good. The number of Fo plants that could be handled in test 

 crosses was quite limited. This may make for greater difficulty in recovering 

 or improving the agronomic type of the sampler lines. It was very evident 

 from field observations that the proportion of agronomically desirable F3 

 lines appeared lower than usually found from crosses of highly selected 



inbreds. 



The greater effectiveness of visual selection among the F2 progenies of the 

 low testing gametes is at this stage only an interesting development. Only a 

 small proportion of the plants arising from the low testing gamete parents 

 exceeded the sampler inbred in performance by a significant amount. 



It was not possible to determine by visual examination which F2 popula- 

 tions were derived from high gametes and which from low gametes, although 

 there were wide differences in plant type between populations. 



Gametes from eight inbred lines compared fairly well with varietal 

 gametes from Morris 13, in offering promising sources of germ plasm for the 

 improvement of specific combining ability of A344. Where a breeder has 

 available large numbers of inbred lines of diverse origin the use of test 

 selected inbred parents rather than varietal gamete parents may be the more 

 feasible approach. Selection for characters other than yield would presum- 

 ably be done more economically. The same advantage can be claimed for the 

 use of complex crosses of inbreds. On the other hand, utilization of varietal 

 gametes in improvement work does not "use up" inbreds so far as their 

 combination in hybrids for commercial use is concerned. Lines recovered 



