| The objective of this study was to determine if zygote selection was a viable method for determining superior material early in the breeding process, using the pedigree system as the ‘default’ method. Lines were derived using the above methodologies from the cross of NC258 and NC296. NC258 is an all-temperate germplasm line while NC296 is a 1st-cycle temperate adapted, all-tropical germplasm line. Results of three-year testcross yield trials revealed that the lines tested were competitive with commercial checks for yield, lodging resistance, and low kernel moisture at harvest. Zygote-derived and pedigree-derived material were also comparable suggesting that zygote selection is a valid way to identify families with good yield potential early in the inbreeding process. To determine if so-called ‘50% tropical lines’ indeed have that percentage of the tropical genome, 33 SSR markers were screened on 132 lines to determine parental contribution. Results showed that in general, the temperate genome is slightly favored, as on average ∼54% of markers from the temperate parent are incorporated. However, 1st-cycle temperate adapted, all-tropical lines do contribute a significant portion of their genome to lines derived from their crossing to elite temperate lines. Lines studied in this thesis by these methods were screened for resistance to the fungus (Cercospora zeae-maydis ) at different generations over different years. Results indicated that early testing may be inefficient in selecting resistant lines as many rank changes occurred between families tested as F2 and Sib 2 testcrosses and their filial lines, likely due to dominance effects. Lines were also screened for the presence of the Ga1-s allele or ‘super-gametophyte’. Homozygous Ga1-s silks cross-incompatible with pollen haplotypes carrying the recessive ga1 allele. Yellow-dent maize in the US is all homozygous ga1, however NC296, a white endosperm line, carries the dominant Ga1-s allele. Results of the screening were well out of line with expectations (30% of lines were homozygous ga1). Two alternate hypotheses are proposed. One, the allele in NC296 is an unknown alternate allele, less ‘strong’ than Ga1-s. Two, modifying genes or epistatic interaction from NC258 reduce the effect of Ga1-s . Further testing is needed to fully explain our results. |
