Graduate Thesis Or Dissertation

An examination of seedling vigor and the effects of genetic diversity on response to heterosis in tall fescue (Festuca arundinacea Schreb.)

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  • Response to heterosis for plant height, anthesis date, panicle number, seed yield, and fall vigor rating was determined in a tall. fescue group selected for diverse morphology, origin, and anthesis date. Parents, single-cross progeny (SX), and first generation selfed progeny (S₁) were included in the study. Each experimental plot consisted of 14 plants spaced three feet apart in a row with four feet between rows. Plants were established in the field in September, 1969, in a randomized block design with four replications. Data were collected during the summer and fall of 1970. Single-cross progeny were superior to parents with the exception of seed yield, with parents above S₁ progeny except in plant height. Single-crosses averaged 15. 36, 2. 60, 28.21, 24. 79, and 23. 04 percent above the mid-parent for plant height, early anthesis date, panicle number, seed yield, and fall vigor rating respectively. Single-crosses averaged 5.85 and 10.27 percent above the high-parent for panicle number and fall vigor rating respectively. Crosses between maturity groups resulted in the greatest heterosis above the mid-parent for all characteristics and above the high-parent for panicle number (117.50 percent of the high-parent). Early x early single-crosses were tallest (106. 49 percent of the high-parent) and had the most vegetative vigor (115. 36 percent of the high-parent). Indications are that crosses between parents of diverse morphology and origin result in a greater expression of heterosis than crosses among similar parents. Diverse anthesis date appears to increase response to heterosis. Vigor and associations among vigor characteristics were determined from single-cross and S₁ seed and seedlings. Respiration, germination, root and shoot growth, rate of growth, and unit growth characteristics were measured using a Gilson differential respirometer and a seed germinator. For most seed and seedling vigor characteristics S₁ 's and SX's were very similar. Early S₁ and early x early SX groups were consistently more vigorous than late S₁ and late x late SX groups with the early x late SX group intermediate between early x early and late x late SX groups for all seedling vigor characteristics. Root length and vigor index were two of the better indicators of early seedling vigor, with vigor index favored because it takes less time to measure and requires less space. Selection on the basis of vigor index should be an effective laboratory method of screening for higher seedling vigor in tall fescue. There was a significant association between most seed and seedling vigor characteristics in SX's and S₁'s, and most seed and seedling vigor characteristics were associated with from one to three mature plant characteristics, most often fall vigor rating. Three methods of selection for high and low seedling vigor (seed weight, head selection on shoot length, and emergence from deep seeding) resulted in small changes in seed weight and vigor index of progeny. Clones from a population with low seed weight and seedling vigor were self-pollinated and topcrossed to a source with high seed weight and seedling vigor. Positive associations between topcrosses and S₁'s for seed weight and vigor index suggests a lack of appreciable heterosis for these characteristics. The association of forage and seed yield was studied in duplicate populations of parents and five progeny groups. These were: first generation selfed (S₁), open-pollinated OP), polycross (PX), single-cross (SX), and selfed single-cross (F ). Nurseries were planted in a randomized block design with four replications, with harvests made during the spring and summer of 1969. There were significant associations of forage and seed yield in four progeny groups with no association in parents and polycross progeny. The highest correlation occurred in the S₁ progeny (r .794). High forage and seed yields in certain OP, PX, and SX progenies indicate the possibility of breeding for both characteristics simultaneously.
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