11
HORE CORRELATIONS OF PARENT VS. OFFSPRING
-SNOW PEAK ANO UHPQUA COAST COOPERATIVES
by Roy Silenl/
How well do progeny tests of parent trees evaluate offspring performance? In
Newsletter No. 44 (page 2) two estimates of parent-offspring correlations were
Correlation
based on data from Vernonia and Molalla Cooperatives.
0.41 and r
0.59 were computed from midparent average
coefficients of r
family height from eight or more sites versus heights of full-sib families
growing at the J. E. Schroeder Seed Orchard.
These coefficients were
considered surprisingly high in view of the hundreds of opportunities for
statistical chatter, damaged plantations, or outright mistakes.
Had the
tallest 20 percent of these parents been placed in an orchard, the seed should
produce families with 5.4 and 9.4 ·percent improved height growth rate.
=
=
Now similar parent-offspring correlations are available for two more
Cooperatives--Umpqua Coast east of Reedsport and Snow Peak east of Albany,
Oregon.
These again provide optimistic data. When family midparent heights
based on family means from eight or more test sites were regressed against
their full-sib family heights in the orchard at age 6 years, the respective
correlation coefficients were:
For Umpqua Coast Cooperative
For Snow Peak Cooperative
r
r
=
=
0.43
0.68
n
n
=
=
98
226
P
P
=
=
0.01
0.001
As in the earlier report, an estimate was made of the percent superiority in
height growth represented by the best 20 percent of crosses, based on their
parental family means in progeny tests.
Umpqua Coast Cooperative orchard
families would average 6. 9 percent superior height and Snow Peak Cooperative
10.6 percent.
A comparison of statistics of the four Cooperatives are best
displayed in a table.
Snow
Peak
Parent-offspring correlation (r)
Height superiority-top 20% parents
0.68
10.6%
Cooperative
Umpqua
Coast
Molalla
0.59
9.4%
0.43
6 .9%
Vernonia
0.41
5 .4%
The major source of difference in r value between Cooperatives appears to be
their relative freedom from problems in the nursery and plantations.
In this
regard Snow Peak and Molalla had least problems, whereas Umpqua and Vernonia
had most. A new factor contributed to the remarkably high r value for Snow
Peak Cooperative. The plan for crossing used 5-year progeny test data, hence
was considerably more structured than the random single-pair matings used by
the other three.
Dr. Roy Silen is project leader of the genetics project, U.S. Department of
Agriculture, Forest Service, Pacific Northwest Forest and Range Experiment
Station, Corvallis, Oregon.
12
The four figures on height superiority represent those families chosen as the
top 20 percent on the basis of family performance in the progeny test. They
estimate the expected growth of seedlings from an orchard of such parents.
This estimate is conservative for the J. E. Schroeder orchard of full-sib
families, as any contribution from within-family selection would be added.
Percent volume superiority would be two to three times as high.
•
HALE VS. FEMALE CONTRIBUTIONS TO FULL-SIB FAMILIES-­
DO WE HAVE A SERIOUS CONCERN WITH ORCHARD CROSSES? by Roy Silen The very large numbers of full-sib crosses in the J. E. Schroeder Seed Orchard
has provided a sensitive direct answer to a serious concern.
Isozyme studies
have suggested that errors in crossing associated with contaminating pollen
sources and with labeling, when done on a commercial scale, could have been
unacceptably high.
If so, the female parent's contribution to height of the
full-sib family should provide a higher correlation coefficient than the
male's contribution when average heights of wind-pollinated families over
eight or more test sites are regressed against the family mean heights of the
crosses in the orchard.
Two Cooperatives provide data for such a comparison, both comparing 6-year
full-sib heights versus 10-year heights of each parent's progeny. One is the
Umpqua Cooperative based on 9B crosses which was studied with isozyme markers
and which was indicated to have many instances of questionable male
parentage. The other, Snow Peak Cooperative, is based on 126 crosses.
In neither case was there any substantial difference between male and female
contribution as measured by correlation coefficients.
For Umpqua Cooperative
n
9B
male
r
female r
For Snow Peak Cooperative
126
n
male
r
female r
=
=
=
=
=
=
0.3 45B
0.3504
0.6906
0.6B22
Such close matching of male and female coefficients means that whatever
problems appear in the crosses concerning inheritance of growth is equally
shared by both male and female contributions.
r