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.
A major limitation to the genetic improvement of wheat (Triticum aestivum L.) is the lack of information about quantitative trait loci (QTLs). The objective of this study was to determine the chromosomal locations of QTLs controlling grain yield and yield components, grain test weight, plant height, and anthesis date. Reciprocal sets of chromosome substitution lines in duplicate between two hard red winter wheat cultivars, Cheyenne (CNN) and Wichita (WI), were used to identify the chromosomes bearing QTLs. Field trials were conducted in Nebraska at Lincoln in 1987, at Lincoln, Mead, and Alliance in 1988, and at Lincoln, Mead, Alliance, and North Platte in 1989. Wichita had major QTLs on chromosomes 3A and 6A that increased grain yield in Cheyenne and major QTLs on chromosome 36 that decreased grain yield in Cheyenne, while Cheyenne had major QTLs on chromosomes 3A and 6A that decreased grain yield in Wichita. The increase in grain yield by WI 3A and WI 6A was due to a significant increase in seed weight. The decrease in grain yield by CNN 3A and CNN 6A was due to a significant decrease in culms per square meter. The decrease in grain yield by WI 3B was due to a significant decrease in winterhardiness, resulting in decreased seed weight and culms per square meter. We identified one Wichita and seven Cheyenne chromosomes with QTLs affecting seeds per culm, seven Wichita and five Cheyenne chromosomes with QTLs affecting seed weight, one Wichita and three Cheyenne chromosomes with QTLs affecting culms per square meter, and one or more chromosomes with QTLs affecting each of the other agronomic traits.
No abstract
Heading date, which is one of the developmental stages of wheat (Tritlcum aestivum L.) that contribute to maturity, is therefore significant trait from an economic standpoint. Reciprocal sets of chromosome substitution lines in duplicate between two hard red winter wheat cultivars, Cheyenne and Wichita, were used to identify chromosomes that carried genes for heading date. The materials were planted in the field at Lincoln, NE using a randomized complete block design with three replications. Heading dates were recorded when 50% of the plants in the two center rows of each four‐row plot had the basal spikelets emerged from the boots. Heading dates were converted to number of days to heading from 1 May for statistical analyses. Wichita appeared to carry major genes controlling heading date on chromosomes 3A and 3D, while Cheyenne carried major genes on 3A, 3D, and 6A. The genes from Wichita accelerated heading of Cheyenne and those from Cheyenne delayed heading of Wichita. Three types of responses were obtained with respect to the duplicates of each substitution line. In the first type, one duplicate differed significantly from its recipient parent but the duplicates did not differ significantly. This behavior could indicate a genetic control of heading date, with Cheyenne chromosomes 1D, 2D, 4D, and 5A having minor effects in Wichita background. In the second type, two lines had significant differences between duplicates and also between one duplicate and its recipient parent. This type of response suggested that there were differences in the genetic backgrounds of the duplicates and that additional backcrosses were needed. In the third type, two lines had significant differences between duplicates but none between either duplicate and its recipient parent, indicating a possible environmental effect.
A major limitation to the genetic improvement of wheat (Triticum aestivum L.) is lack of information about the effects of quantitative trait loci (QTLs) on stability of agronomic traits across environments. Our objective was to determine the chromosomal locations of QTLs controlling stability of grain yield and yield components, grain test weight, and plant height. Reciprocal sets of chromosome substitution lines in duplicate between two hard red winter wheat cultivars, Cheyenne and Wichita, were used to identify chromosomes that carried QTLs affecting stability. Data from the two parental cultivars, 40 Wichita chromosome substitutions in Cheyenne, and 34 Cheyenne chromosome substitutions in Wichita, grown in six environments in Nebraska, were used to compute the regression coefficient on the environmental index (b1), the mean square of the deviation from regression (S2d), and the coefficient of variation (CV). Little variation existed among the substitution lines for S2d and CV, so bl was the primary stability parameter used to describe the lines. Wichita had one or more major QTLs on chromosomes 3A, 6A, 2B, and 3D that increased b1 of grain yield in Cheyenne. Cheyenne had one or more major QTLs on chromosome 1D that decreased b1 of grain yield in Wichita. We identified one Wichita and two Cheyenne chromosomes with QTLs affecting stability of seeds per culm, one Wichita and three Cheyemme chromosomes with QTLs affecting stability of seed weight, nine Wichita and eight Cheyenne chromosomes with QTLs affecting stability of culm per square meter, and seven Wichita and four Cheyenne chromosomes with QTLs affecting stability of grain test weight.
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