Improvement of expansion volume, defined as the volume of popped corn per gram of unpopped corn, generally is considered the most important objective of popcorn (Zea mays L.) breeding programs. Popcorn, however, generally is inferior to dent corn with respect to yield and other agronomic characteristics. Detailed information on the inheritance of expansion volume and grain yield in popcorn ✕ dent corn crosses was not available in the literature. The objective of this study was to determine the inheritance of expansion volume and grain yield, including yield components, in two popcorn ✕ dent corn crosses. Generation means analysis was used to quantify genetic effects in the popcorn ✕ dent crosses Ia53 ✕ B73 and Ia28 ✕ Mo17. Significant additive genetic effects were detected for ail traits in both crosses. Significant dominance genetic effects were detected for expansion volume in the cross Ia28 ✕ Mo17, and for grain yield, ear length, ear diameter, and 5O‐kernel weight in both crosses. Dominance effects resulted in reduced expansion volume, and increased grain yield, ear length, ear diameter, and 5O‐kernel weight. Significant epistatic effects for grain yield were detected in the crosses Ia53 ✕ B73. Expansion volume was negatively correlated with all yield components except for number of kernel rows. Thus, relative to other yield components studied, selection for high kernel row number would appear to result in the least reduction of expansion volume. Results from this study indicate that breeding methodologies which exploit additive genetic variation assoicated with expansion volume and dominance variation associated with grain yield are most likely to result in concurrent improvement of these two traits.
Expansion volume, defined as the volume of popped corn per gram of unpopped corn, is considered the most important quality trait in popcorn (Zea mays L.). The increasing popularity of microwave popcorn has necessitated the development of cultivars for use in both conventional and microwave popping. Information on expansion volume of popcorn genotypes using both popping methods is not available in the literature. This study investigated the presence of a genotype ✕ popping method interaction for expansion volume and its components in popcorn. Eleven commercial popcorn hybrids, one flint corn ✕ popcorn inbred line cross, and one open‐pollinated popcorn variety were grown in isolation in 1988. Seed harvested from each genotype was divided equally into large‐ and small‐kernel samples that were evaluated for expansion volume, popped kernel (flake) size, and percent unpopped kernels in conventional and microwave popping. All genotypes performed better in conventional popping than in microwave popping. Significant differences existed among genotypes for expansion volume and flake size. A significant genotype ✕ popping method interaction was detected for expansion volume, flake size, and percent unpopped kernels. Therefore, breeders utilizing germplasm similar to that which we studied with the dual objective of developing cultivars for conventional and microwave popcorn markets should conduct evaluations for expansion volume using both popping methods.
Variation in recombination rate is important to plant breeders since a major objective is to obtain favorable recombinants of linked genes. The ability to increase recombination (R) in circumstances in which favorable and unvavorable genes are linked (Corn Belt x exotic populations) and to decrease recombination when many favorable genes are linked (narrow-based, elite populations) would be of immense value. However, the concept of variation in recombination frequencies between linked genes has received limited attention despite its implications in breeding and genetic linkage studies. Molecular techniques have allowed better estimations of this variation. In this study, attempts were made to characterize: (1) the R values in the Pgm1-Adh1 and Adh1-Phi1 adjacent regions of chromosome 1 and the Idh2-Mdh2 region of chromosome 6 in F2 families of three maize (Zea mays L.) populations; (2) the environmental effect on R values of F2s from two populations. One population, NSO, was a Corn Belt synthetic, and the other two populations, CBMEX3 and CBCAR5, were composites from crosses between Corn Belt and exotic germ-plams.Wide ranges of estimated recombination ([Formula: see text]) values were observed among families in each population for all three chromsomal regions. The distribution of [Formula: see text] values for the Pgm1-Adh1 region showed that the F2 families of each population fell into two broad categories: 0.30-0.50 and 0.02-0.20. No intermediates (0.21-0.29) were found. The distributions were almost normal for the Adh1-Phi1 and the Idh2-Mdh2 regions. It would appear that the major dispersion in the Pgm1-Adh1 region was controlled by the effects of a single gene, while the Adh1-Phi1 and Idh2-Mdh2 regions were only affected by polygenes. No correlation was found between recombination values of the two adjacent regions, indicating that the genes affecting recombination for the Pgm1-Adh1 region may be specific for that region.For the Pgm1-Adh1 region, no differences in [Formula: see text] values were found among the three populations. For the Adh1-Phi1 region, [Formula: see text] frequencies of CBMEX3 and NSO were not significantly different, but both had significantly greater [Formula: see text] values than CBCAR5. For the Idh2-Mdh2 region, CBMEX3 was significantly different from NSO. There were significant differences between some paired F2 families within each population for each chromosome region.No significant differences in response to the two environments were detected in CBMEX3 and NSO for either region in chromosome 1.
Near‐isogenic lines (NILs) have been developed in a number crop species via the backcross breeding method. These NILs possess remnant donor parent (DP) DNA, some of which is present in the chromosomal segment linked to and surrounding the introgressed marker. If this DP‐derived DNA contains molecular marker loci (i.e., isozyme variants or restriction fragment length polymorphisms) for which a recurrent parent (RP) and DP possessed allelic contrasts, then DP‐derived molecular alleles may still be present in an NIL and could be detected a posteriori by molecular genetic analysis of specific trio sets of RP/NIL/DP lines. Given this proposition, our objective was to provide a theoretical basis for evaluating the results of such analyses. Using equations derived by previous workers, we calculated that about four of 100 randomly chosen DP‐derived molecular markers would be expected to be retained in a BC5S1 NIL constructed in a hypothetical species with 20 chromosomes of equivalent 50 centimorgan (cM) genetic map lengths. Of these four markers, two or three would be expected to be located on the introgressed marker chromosome. This suggests that a near‐isogenic gene mapping technique would provide a means for subsetting molecular and introgressed markers into presumptive linkage groups. Such a priori information would make traditional methods of integrating both marker types into a single linkage map a much more efficient undertaking. A combined linkage map would be a valuable resource relative to the goal of eventually cloning some of the conventional markers of scientific interest or economic value.
Near‐isogenic lines (NILs) have been proposed as a genetic resource that can be used to identify linkages between molecular and conventional markers. If the donor parent (DP) and the recurrent parent (RP) possess an allelic contrast for the molecular marker, and if the DP allele is still present in the NIL, then presumptive evidence of linkage between that molecular marker and the intro‐gressed gene can be inferred. The objective of this study was to evaluate this NIL gene‐mapping technique using isozyme markers and a collection of 63 soybean [Glycine max (L.) Merr.] NILs. The electrophoretic isozyme banding patterns of eight enzymes (12 loci) were examined in 35 ‘Clark’ and 28 ‘Harosoy’ RP/NIL/DP trio sets, where each NIL possessed an introgressed conventional gene. Of the 756 combinations of 12 isozyme loci and 63 trio sets evaluated, 256 exhibited RP/DP isozyme allelic differences. Of these 256, seven (four in Harosoy, three in Clark, total of five conventional markers) exhibited an RP/NIL contrast and a corresponding NIL/ DP equality for an isozyme allele. The five different presumptive linkages were: Enp – In, Mpi – dt2, Aco4 – dt2, Mpi – ln, and Pgi – d2. The F2 cosegregation data confirmed the presumed linkages of Enp with ln (9.38 ± 1.55%) and Mpi with dt2 (16.07 ± 6.43%), but refuted the presumed linkages of Aco4 – dt2 and Mpi – ln. The Enp locus is therefore part of Linkage Group 4, which is currently comprised of the v1, ln, and P2 loci. Neither Mpi nor dt2 have been assigned to an existing linkage group, and thus represent a new linkage group. The presumed linkage of Pgi with d2 was not tested, but other data indicated that this presumption was probably erroneous. The confirmation of two of the five presumptive linkages was consistent with the numbers expected based on a previously published theoretical analysis of the NIL gene‐mapping technique.
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