The objectives of this study were to determine whether epistasis plays a significant role in the genetic systems for selected traits among several winter wheat (Triticum aestivum L. em Thell.) cultivars and to evaluate the importance of additive vs. dominance gene action for traits not influenced by epistasis. In each of two replicated experiments, two cultivars (referred to as testers L1 and L2) and their F1 (L3) were crossed to each of 10 other cultivars and evaluated in a single field experiment. The deviations (cultivar ✕ L1 + cultivar ✕ L2 — 2 cultivar ✕ L3) were analyzed to provide a test for epistasis. An additive‐lominance model was fitted to the data for those characters not affected by gene interactions.Results of the two experiments were generally consistent with respect to the detection of epistasis. Epistasis affected the expression of heading date, kernels/spikelet, and grain yield, but not of plant height, protein content, tiller number, spikelets/spike, and kernels/spike in both experiments. Epistasis was indicated for kernel weight in one experiment but not the other. Expression of epistasis was influenced by particular cultivars, indicating that a limited number of cultivars may not be sufficient to detect nonallelic interactions for a character within this species.Additive gene action was predominant in both experiments for protein content, spikelets/spike, and kernels/spike, suggesting that improvement of those characters can be achieved through standard selection procedures. Evidence for dominance gene action was obtained for plant height and kernels/spike in one experiment.The results of this study indicated that epistasis may be a nontrivial factor in the inheritance of agronomic traits. Genetic models neglecting epistasis may result in biased information.

Genes that affect plant form and function may be used to enhance the yield of soybean [Glycine max (L.) Merr.]. Most soybean cultivars have broad (ovate) leaflets. A single gene, ln, controls inheritance for the narrow leaflet characteristic. Narrow leaflet cultivars (ln/ln) also tend to have a higher percentage of four-seeded pods than ovate (Ln/Ln) leaflet cultivars. Heterozygous (Ln/ln) plants have a leaflet shape intermediate between narrow and ovate. Determining the agronomic effects of the narrow leaflet allele (ln) in the heterozygous (Ln/ln) condition in soybean may have applications in practical plant breeding. We studied an ovate leaflet and a narrow leaflet cultivar, crosses between them in the F(1) and F(2), and backcrosses to both cultivars. The ratio of leaflet width to leaflet length accurately distinguished among narrow, ovate, and intermediate leaflet plants in the F(2) and backcross generations. In the F(2) generation, differences occurred among plants with different leaflet morphology. Narrow leaflet plants produced more seeds per pod and lower seed weight than ovate leaflet plants. Narrow and ovate leaflet plants produced comparable numbers of pods per plant and plant yield. Compared to ovate leaflet plants, intermediate leaflet plants produced similar numbers of seeds per pod and seed weight. Intermediate leaflet plants produced significantly more pods per plant and plant yield than plants with either ovate or narrow leaflets. The heterozygous condition at the locus for leaflet morphology resulted in heterosis for plant yield and may be of benefit in association with commercialization and development of hybrid soybean.

Parents, F19, F29 and first generation backcrosses (B1 and B2) of a ‘Centurk’ ✕ ‘Bezostaia 1’ cross (Triticum aesti. vum L.) were grown in a space‐planted experiment to obtain genetic information pertaining to grain yield and seven other agronomic characters.The F1 deviated significantly from the midparent values for heading date, plant height, and kerneis/spikeiet indicating a sizable amount of nonadditive gene action for those traits. Narrow‐sense heritability estimates were very high for heading datea moderately high for kernel weight and plant height, moderate for number of tillers/plant, and low for spikeiets/spike, kernels/spike, kernels/spikelet, and grain yield. Several of those estimates were considered biased upwaxd as epistasis was found to contribute significantly to heading date, plant height, tiller number, kernels/spikelet, and grain yield. No epistasis was detected for spikelets/spike, kernels/spike, or kernel weight, indicating that estimates of gene effects for those characters were free from linkage bias. Duplicate epistasis was detected for heading date and grain yield, suggesting difficulty would be encountered in selecting for earlier maturity or higher yield in this cross. Additive effects were the main source of genetic variation forkernel weight, indicating that early generation selection for higher kernel weight should be effective in this material. The prospects for increasing tiller number were not as favorable as were those for kernel weight.

Two winter wheat (Triticum aestivum L. em thell.) crosses were used in this study to determine the type of gene action involved in the expression of a number of agronomic characters. An unweighted least squares procedure was adopted to analyze means of parents, F1, and first generation backcrosses from each cross. Only additive gene effects were significant for plant height, number of tillers/unit area, and kernel weight, indicating possible improvement of these characters through selection in early generations. Heading date was controlled by genes with additive and dominance effects which indicates that selection for this trait would be more effective if delayed until later generations.

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