Graduate Thesis Or Dissertation
 

Combining ability and gene action estimates and the association of the components of yield in winter wheat crosses

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  • A diallel cross consisting of ten parents was grown on the Hyslop Agronomy Farm near Corvallis, Oregon, in order to obtain estimates of the gene action contributing to yield and its components in wheat. Gene action estimates were obtained by two methods of diallel analysis and from narrow sense heritability values calculated by parent-progeny regressions involving both parental and F[subscript 1] data. In addition, path-coefficient analysis was utilized to investigate the direct and indirect associations of five variables on yield. The morphological characters measured were: (1) total yield per plant, (2) weight per kernel, (3) number of kernels per spikelet, (4) number of spikelets per spike, (5) number of spikes per plant and, (6) plant height. A large portion of the total genetic variation associated with the yield components, weight per kernel, kernels per spikelet, spikelets per spike and spikes per plant was the result of additive gene action. When the five variables were considered in terms of their associations with yield it was observed that weight per kernel, number of kernels per spikelet and the number of spikelets per spike mainly exerted direct effects on yield. The number of spikes per plant had no direct effect, but an indirect effect on yield through the other variables. A similar indirect association was noted for plant height. The data obtained from the path-coefficient analysis indicated further that the number of kernels per spikelet had the greatest direct effect on yield. Results obtained with correlation coefficients suggested that a negative association exists between weight per kernel and kernels per spikelet. Also such a negative association was found between the number of spikes per plant with weight per kernel and kernels per spikelet. These results would suggest the possible existence of a biological limitation between several of the components of yield. The diallel cross analysis for general and specific combining ability gave similar estimates of gene action when they were compared to narrow sense heritability values. However, when the Jinks-Hayman method was compared with the other two methods of estimating gene action, several discrepancies were observed. This lack of agreement was possibly due to the inability of this experimental material to meet one or all of the genetic assumptions required by the Jinks-Hayman method. The results of this study indicate that a breeding program with emphasis on increases in yield which considers each of the components separately, or in combination of two or more would offer the most promise. By this procedure the breeder could take advantage of the large amount of additive genetic variance associated with each of the components and at the same time, take into consideration any biological limitations which may exist. In utilizing the information obtained in this study in such a breeding procedure the plant breeder would be able to better evaluate the methods for selecting the best parents to be hybridized and in selecting the best lines from hybrid progeny.
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