Graduate Thesis Or Dissertation
 

A study of methods of parental evaluation using testers to predict subsequent progeny performance in winter wheat (Triticum aestivum L.)

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  • The major objective of this study was to determine why certain winter wheat cultivars, when hybridized, will produce a greater proportion of desirable plants in subsequent, segregating generations. Three winter wheat parents were chosen as the experimental material, based on their known performance as parents. Yamhill and Pullman Selection 101 are recognized as cultivars with good combining abilities for grain yield. Crosses with Nugaines have been disappointing, even though the cultivar itself is high yielding. Each parent was crossed to a series of five testers. These testers were chosen on the basis of their genetic diversity, especially for the components of yield. This parent x tester crossing scheme was analyzed as a 3 x 5 factorial, where the main effects due to parents and testers were their general combining ability effect estimates. The interactions of these main effects were their specific combining abilities. F₁ hybrids were evaluated for two years and F₂ populations for one year to characterize the parents' capacity to transmit selected attributes to their resulting progeny. These generations were evaluated on a per plant basis for their grain yields and the primary components of yield, tillers per plant, kernels per spike, and 1000 kernel weight. The four methods of evaluating parents assessed were parental performance, midparent-progeny correlations, examination of individual crosses, and combining ability analysis. Midparent-progeny correlations usually were not significant within the progeny of each parent. Significant differences were not found for grain yields among the parents in either year. However, significant differences existed for their expressions of yield components. Parental expressions of the yield components were generally more erratic than those of their F₁ progenies. Significant differences occurred for estimates of general combining ability effects in both years and for each generation in all traits. These estimates for a particular parent were relatively consistent. Specific combining ability was not found to be a dependable means of identifying superior combinations. Associations between the parental general combining ability effect estimates for kernels per spike and 1000 kernel weight were positive. Relationships between other yield component combinations were negative with regard to general combining ability effects. Trends observed in single crosses reflected the relative general combining abilities of the parents. Crosses involving Yamhill generally had fewer tillers with a higher number of kernels per spike, heavier kernel weights, and superior grain yields to those of the other parents. Progeny of Pullman Selection 101 were usually high in tillering, intermediate for number of kernels per spike, low in kernel weights, and intermediate for grain yields. The progeny of Nugaines were characterized by high tillering, a low number of kernels per spike, low kernel weights, and also low grain yields. The parent x tester crossing scheme was found to be an effective way of determining the potentials of the three parents by estimating their general combining abilities, as well as minimizing the number of crosses required. If, as found in this study, the general combining ability effect estimates of the parents for grain yield accurately predict performance of later generations, this parent x tester crossing scheme would be an efficient method of assessing the potentials of prospective parents in breeding programs.
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file details AlexanderWilliamL1980.pdf 2017-08-17 Pubblico Scaricare