Graduate Thesis Or Dissertation
 

Heritability estimates for seed and plant characteristics in white clover (Trifolium repens L.)

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  • Genetic differences, extent of hybrid vigor, nature of gene action, heritability estimates, and associations among characteristics, and between progenies and their respective mid-parents were determined for seed and plant characteristics in white clover (Trifolium repens L.). Ten seed and seedling vigor characteristics, including seed weight, ATP content in seed, seed respiration, and seedling vigor index were studied for a diallel cross consisting of 28 single crosses, five test-crosses, four checks, and eight open-pollinated seed and seedlings. Twenty-three plant characteristics on stolon, petiole, leaf, and forage were examined on the eight clones diallel cross, five test-crosses, three checks, the eight parental clones of single crosses, and six parent clones of the test-crosses. These 14 parent clones for this study were assembled on the basis of diverse morphology and origin. Most seed and seedling vigor characteristics, except RQ values, and most plant characteristics, except internode length, LAR and diurnal ratio in SLW, expressed significant differences among and within most groups of progenies and parental clones. All seed and seedling vigor characteristics, except RQ values, responded primarily to the nonadditive type of gene action. This suggests that the plant breeder should design his breeding program to develop varieties where hybrid vigor can be used to advantage. Among the criteria used in this study to measure seed and seedling vigor, ATP content per seed was closely associated with seedling vigor index and with certain plant characteristics, including forage yield per plant. The associations of seed weight with other seed and seedling vigor characteristics were negative or poor. Most plant characteristics showed apparent hybrid vigor when progenies were compared with their respective mid-parents. With few exceptions, most plant characteristics, stolon, petiole, leaf and forage yield per plant, responded primarily to the nonadditive gene system. This indicated that the plant breeder may use the hybrid approach to white clover variety development. The exceptions were leaf ratio and SLW which responded primarily to additive gene action, and area and dry weight per leaf appeared to respond equally to additive and nonadditive gene action. Genetic differences were more readily identified for stolon number and length when measurements were taken after 70 days of growth. Yield components, such as number, length, and diameter of stolon, petiole length, number of leaves per plant, and dry weight per leaf were closely related to each other. The leaf components of yield, dry weight per leaf and number of leaves per plant, had the highest direct and indirect effects on forage yields per plant among the yield components. This study showed nonadditive gene action primarily responsible for most seed and plant characteristics. Considering the ease of vegetative propagation in this species along with the self-incompatibility, mechanisms, it is suggested that parent geneotypes may be developed by some recurrent selection procedure, then crossed on a two clone synthetic basis to form experimental lines for testing purposes.
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