Heterosis and inbreeding in the progeney of genetically diverse parental clones of Festuca arundinacea Schreb Public Deposited

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  • The response of maturity, vigor, plant spread, plant height, three forage harvest yields, and total forage yield to heterosis and inbreeding was studied in tall fescue. Parent clones selected for diverse anthesis date, origin, and morphology were separated into two groups based on anthesis date, those having early maturity and those having late maturity. Parents, single-cross (SX), and first generation selfed (S₁) progeny were field evaluated. Parents, S₁, and SX progeny were space planted on a . 914 x 1.219 meter basis at the Hyslop Agronomy Field Laboratory, Corvallis, Oregon, in September, 1969. A randomized block design having four blocks and 14 plant rows as entries was used. Data were collected during the spring, summer, and fall of 1972. Single-cross progeny had a mean performance better than their midparents ' mean performance for all characteristics, with all differences significant except for plant height and third harvest forage yield. Single-cross progeny averaged 7. 03, 13. 18, 13. 50, 3. 89, 42. 93, 51. 72, 15. 14, and 37. 12 percent better than their midparents for maturity rating, vigor rating, plant spread, plant height, first, second, and third harvest forage yield, and forage yield, respectively. There was a greater frequency of individual single-crosses that exhibited significant heterosis in the early x late group than in either the early x early or late x late groups. In addition the average heterotic response of the early x late group was consistently greater than that of either of the other two groups. Thus it appears significant heterosis is more likely to occur, and is likely to be of a greater magnitude, in the progeny of parents having maturity differences, and presumably, greater genetic differences. Significant variation occurred among the single-cross maturity group means for all characteristics with the early x early single crosses most often being the better performers. Consequently the additional heterosis observed in the early x late group was usually insufficient to bring performance of this group up to that of the higher performing but less heterotic early x early single-crosses. This suggests heterosis may be of little practical importance. Inbreeding depression of S₁ progeny was significant for all characteristics. The inbreeding depression was of the greatest magnitude in the progeny of the early parents. Performance of early parents and early S₁ progeny was generally better than that of their late counterparts. Heritability estimates were high, particularly those obtained by regressing single-cross progeny on midparents, although two did not differ significantly from zero. The coefficients of determination for the same associations were likewise high, with over 70 percent of progeny variation being explained by linear association with parents for most characteristics. As superior progeny came from superior parents, this high degree of association suggests clonal evaluation may be an effective screening method in tall fescue. There was strong association among the characteristics of maturity rating, plant spread, plant height, first and third forage yield, and total forage yield, with the lowest of these coefficients of determination, R² = .6031, occurring between maturity rating and plant spread. Vigor rating, second harvest yield, seedling vigor index, and panicle number showed little association among themselves or among the other characteristics, with the highest association, R² = . 3599, occurring between panicle number and third harvest yield. Seed yield was moderately associated with forage characteristics, with R² values of about .5000, but showed no association with panicle number.
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