|Abstract or Summary
- The single-cross and most F₂ progenies of 19 genotypes of
tall fescue (Festuca arundinacea, Schreb. ) were used to study the
breeding behavior of forage yield. Parental genotypes were selected
for high self-sterility, high chromogen and high crude protein. These
were studied in two groups of nine intermediate and ten late-flowering
Progenies were grown on the Hyslop Agronomy Farm, Corvallis,
Oregon as plants spaced one foot apart with three feet between
rows. Ten plants of each cross for each generation were arranged in
a randomized block design with four replications. Variables measured
were plant width, natural plant height, plant spread, leaf length,
total plant height of regrowth tissue, plant density and forage yield.
The collected data were converted to plant means.
Broad- and narrow-sense estimates of heritability were obtained from expected mean squares according to Griffing's analysis
(random model, method four) and compared with estimates of heritability
obtained by F₂-single-cross regression. General and specific
combining ability effects were observed and the single-cross-F₂ inbreeding
depressions were studied. The F₂ families were obtained
by the self-pollination of five single-cross plants.
General combining ability mean squares averaged from two to
nine times greater than the mean squares for specific combining
ability, with the largest difference being 54.7 times greater. The
two populations responded similarly for the variables measured except
for total plant height and plant spread. Greater progress from
selection could be expected in the late- maturing group with the exception
of these two traits.
In most cases, single-cross progenies performed better than
their corresponding F₂ progenies. The average of all single-crosses
differed from the average of all F₂ progenies in 12 of 20 analyses in
1963, but in only 2 of 12 in 1964. The inbreeding characteristic was
most pronounced for forage yield. High-performing single-crosses
for the traits studied tended to produce high-performing F₂ progenies.
Little or no heterosis was expressed and the expression of inbreeding
depression appeared to be influenced greatly by the environment.
Heritability estimates indicated that most traits could be
studied more effectively after the second year of plant establishment. The environmental influence appeared to be less pronounced at that
time. Where the coefficient of determination was high between the
single-cross and F₂ generations, traits were less influenced by the
environment and the disparity between the estimates of heritability
was less. When used on cross-pollinated polyploid grasses, the
method of diallel analysis proposed by Griffing does not appear to
remove all environmental influence and thus overestimates heritability.
Forage yield in the two populations of tall fescue studied was
governed principally by additive gene action. Heterosis expressed
was mostly in crosses involving low-performing parents.