- 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
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