A Study of Genetic Control of Bud Bursting in Douglas-Fir Roy R. Sileo
SEASONAL growth patterns
influ­
ence a tree's adaptiveness to a par­
ticular site (1) and perhaps such
important traits as snmmerwood
ratio in the annual ring (.2, 9).
Observations started in 1933 have
shown
that
Douglas-fir,
growth
patterns
in
particularly the bud
bursting trait are very consistent.
While the date that bud bursting
starts may be early or late, depend­
ing on spring weather, the order of
A randomized block design w:is
used for the experiment with three
fluences. Occurrence of a random
pattern in bud bursting of the
scions would have indicated re­
replications
sponse to environmental influences.
Conversely, the original order of
types, or 21 grafts assigned ran­
domly to 21 limbs in the upper half
bursting of the scion types on all
understocks would indicate strong
genetic control of the trait.
of the crown of each understock
The experiment was established
in 1955. Scions from six Douglas­
grafts.
fir trees, known from years of ob­
servation to have widely differing
of
the
seven
scion
tree. Since seven understock trees
were used, this gave a total of 147
High mortality
vras
ex.
pected among these limb grafts.
The use of three grafts of each
scion type on every understock tree
was in the hope that at least one of
bursting for a group of trees is
dates of bud bursting, were grafted
practically the same year after
year .1 From provenance studies
onto clonal Douglas-firs. Observa.
tion of bud bursting dates in 1956
each type might survive.
this order of
bursting has been
and 1957 indicated there was a
March 5-6, 1955.
proved to be under some degree of
high degree of genetic control of
taken from the upper third and
genetic control, since the same races
this trait. Information on some re­
lated questions was also obtained.
south side of crowns of the parent
burst in the same relative pattern
in planting sites at both low and
high elevations ( 6). A means of
Materials and Methods
This study was based on a 12-tree
estimating the degree of this ge­
netic control was the objective of
this study.
The approach to studying the de­
gree of genetic control was to select
clone of 17-year-old Douglas-fir (5)
growing an a 1/5-acre area of the
McDonald Forest near Corvallis,
Ore.2 Seven trees of the clone, rang­
ing in height from 14 to 25 feet,
trees displaying wide differences
in date of bud bursting; it was
hoped thereby to maximize genetic
differences. Scions from these tree•
were grafted onto clonal under­
stock grown in a very limited and
uniform area. This eliminated ge­
netic variation in the understock
and minimized environmental inTHE AUTHOR is a research forester, Pa­
cific Northwest Forest and Range Expt.
Sta., Forest Service, U. 8. Dept. Agric.,
Portland, Ore. Be is stationed at Cor­
vallis in cooperation with the School of
Forestry, Oregon SU..te University.
The study was planned and established
jointly by R. R. Silen and H. lrgens­
Moller, geneticist, School of Forestry,
Oregon State University. Field measure­
ments and analysis were made under the
author's direction.
1.W. G. Morris of the Pacific North­
west Forest and Range Expt. Sta. has
kept continuous
phenological records
since 1933 on many Northwest speeies.
The aix trees provided tor the study are
among those on which he has long rec ·
ords.
were used as understock for the
study.
·
Scions of this understock, usually
cut from the same limb, were graft­
ed as controls.
Other scions were
gathered from each of three trees
from two locations :
Locati01t and
re1ati11e time
of bud burstin-g
Elevation of
scion tree
parenf
(Feet)
Corvallis clone: A (Control)
Portland, Ore.:
B (Early)
0 (Intermediate)
D (Late)
8.W. Washington:•
E (Early)
F (Intermediate)
G (Late)
·---·········-····--
···-··-·······--···-
·--·-
·
----·-··
---····----
··--·-
···············-··-----
300
800
800
750
500
400
500
his clone was established in 1939 by
Dean W. F. McCulloch, Oregon State
University, as rooted cuttings from 1·
year-old wood from a single limb of a
tree on the 0.8.U. campus.
8Elevation has been found to be a fac­
tor related to bud bursting of Donglas­
472
Scion material was collected on
Cuttings were
trees, except in the case of tree E.
This codominant tree was too slen­
der, due to competition, to allow
climbing high in its crown, so scion
material was collected from the cen­
tral branches. Three to six large
limbs were cut from each tree. Cut­
tings were stored under wet burlap
in continuous shade during cool
weather until March 21-24 when
understock trees were at the de­
sired stage of growth for grafting.
The best scions from each limb,
generally including terminal buds
of the branchlets. were used for the
grafts.
Whip grafts were employed,
using only first-year wood in 2- to
3-inch lengths as scion material.
Understocks were often cut back to
second-year wood.
Grafts were
coated with asphalt emulsion wax,
and each scion was protected for
about a month with a polyethylene
bag enelosed by a ventilated kraft
bag.
Records were kept of bud burst­
(1, 6, and7).
'In the Douglas-:fir heredity plantation,
Wind Ri'ter Experimental Forest, Carson,
Wash., ele'tation 1,150 feet. E and G are
from seed collected near Granite Falls
and F from seed collected near Fortson,
both in northwestern WaRhington.
:fir
473
JULY1962
Results
ing date, elongation, and survival
of each graft as well as for three
ungrafted
limbs
per
understock
There was regular and highly
tree. Bud bursting was defined as
significant
progression
in bud
bursting of the grafted material in
the date when the first green needle
accord with relative time of bud
could be seen through the ruptur­
ing, papery scales of the expanding
bursting of trees from which scions
viere collected (Fig. l). This held
bud.
Observations were made at
true for both years of observation.
least twice weekly during spring
During the sum­
Genetic effects, as expressed by
variation in bud bursting time of
mer, when little growth was occur­
the several scion types, were sig­
1956 and 1957.
ring, observations were made at
intervals of one week or longer,
terminating each year in late Sep.
tember.
Analysis
Analysis of variance "·as made
nificant
at
the
1-percent
after earliest bud bursting, April
22. Bud bursting for each scion type
was recorded on the earliest burst­
ing bud of the best surviving graft
on each understock tree.
Because
was used on each understock tree
so that as many scion types as pos­
sible could be included in an ortho.
gonal analysis.
A similar analysio
was made of the 1957 data, but
April 19, the date of earliest bud
and intermediate scions from south.
west Washington reduced the num­
ber of understock trees having all
seven scion types for this analysis
to five in 1956 and four in 1957.
Estimates of the genetic component
of variation for each year's data
were made
OF
CORVALLIS
CLONE UNDER STOCK
A
CORVALLIS
CLONE
GRA TS
B
PORTLAND
( Early
l
c
PORTLAND
I lnfermedicrte )
D
PORTLAND
( late)
E
WASHINGTON
variance, using data on total elon­
(Early )
A regression was also com­
puted for the above bud-bursting
dates, usng total elongation as the
independent variable.
r;Computed
fron1
formulas:
Mean
square for scion types = a2 + Koo'
and genetic component
ao'
= ---- in '"·bieh a'
APRIL
20:2530
SCIONS
{ Bud bursting time
of pcrent tree )
growth was made by analysis of
tree.
=
er or mean
square, OG2 = genetic variance, K
Dumber of clonal trees.
=
729.25
558.24
15.82
10.16
5.25
Error
9.15
A multiple range analysis of the
1956 data showed that average time
of bud bursting of all the scion
F
WASHINGTON
( lntermediofe )
G
WASHINGTON
(Late l
1957
1956
SOURCE
MAY
" 20 25 "'
5
· · ·
: :J •JI
::F
,E
.
:
JUN
4
9
®
:
: r'[
'.f
5 10
0
MAY
15 20 25 30
JUNE
4 9
'
'
------
®
[
®
5E
2025
®
I
.l
Ji.
APRIL
w.
t,
Li_L_
®
>
"'
gation of the best surviving graft
of each type on the understock
Scion types
Clonal understock
1957
group where differences averaged
only 2.2 days (Fig. 1).
(4) .•
A test for differences in scion
Mean squares
1956
squares from the analysis of vari­
ance sho,vs variability due to scion
burst, was used as the beginning
date. Death of many grafts of early
Source of
variability
types differed from one another
with exception of the Portland
of high mortality of some scion
types, only the best surviving graft
times larger for 1957 than due to
understock effects:
ences within the plot, was not sig­
nificant. A comparison of the mean
on 1956 bud-bursting data, using
as the variable the number of days
level.
Variation attributed to understock,
a measure of environmental differ.
types more than seventy times larg­
er for 1956 and more than thirty
I
11
.
[
I
I
..
1ll
1A.1
II
I ..
I
•I•
,
'
®
II I
!
[
II
'
,
I I
,..
'
F1a. 1.-Frequeney distribution of bud bursting dates for clonal understock and
grafts of the clone, including three Portland, Ore., and three western Washington
trees. Average date of bud bursting is shown by a trta.ngle below each distribution.
Circled X marks date of bud bursting of parent trees in Portland and Corvallis. No
bud bursting records were kept of the Washington trees.
JOURNAL OF FORESTRY
474
Estimates of the genetic compo­
nent of the bud bursting time were
Initial success of grafting, meas­ bursting time seen in the forest have
a completely genetic basis. That
ured by formation of definite un­
this is not so, but applies only to
the narrow environmental range
very high for the scion types-96­
percent for the 1956 observations
and 94 percent for the 1957 obser­
vations. This means that practically
ions between scion and understock,
types.
of this experiment, is shown by the
Seventy-one percent of an grafts
following observations from this
an the variability was genetic in the
sense that differences in time of bud
were judged successful on July 13
of the first growing season. At this
and other studies.
Environment also plays a large
part in the bud bursting pattern
seen in the forest. For example, the
showed far closer relationship to
understock
than to scion
bursting of the seven scion types
time, grafting success by various
were consistent and little differ­
ence was shown from one under­
scion types
_ showed relatively small
stock tree to the next.
percent.
However, the range of
range in average date of bud burst­
ing for scions of the three Portland
nonsignificant variation-57 to 81
Growth rate of the grafts also
success by understock trees was 43
trees was only 2 days in 1956 and
differed widely and significantly by
scion types. Greatest growth oc­
to 100 percent, a highly significant
variation. Since the understock was
3 days in 1957. At Portland these
same trees have burst their buds
curred on the control grafts made
by cutting off a scion and regrafting
it to the same limb. Their seasonal
without genetic variation, signif.
icant variation in grafting success
indicates that some physiological
ing 11 years of observation. This
growth averaged 7.4 inches on Au­
condition of the understock trees
were small, but consistent environ­
over a period of 7 to 14 days dur­
suggests that genetic
differences
gust 9, 1957. Scions of the three
such as vigor was different. There­
mental differences were appreciable
trees from Portland averaged 3.8
fore, an analysis was made on the
inches, whereas scions from Wash­
assumption that height was an ex­
between the three trees on tbe same
hill at Portland.
ington trees
inches.
pression of vigor. Grafting success
Another example related to the
was not found to be significantly
natural stand surrounding the
clone. Bud bursting of the mature
averaged
only
1.8
Bud bursting date was correlated
related
to heights of
the
seven
with growth rate. In general, early
clonal trees, although a trend to­
bursting scions of the clone grafts
and Portland trees made the great.
ward such a relationship was indi­
trees averaged nearly two weeks
later than their seedling progeny,
presumably beeause of the more
shown by the late bursting Wash­
ington scions. About 65 percent of
cated.
By the beginning of the second
year, death of additional grafts
gave further evidence of the same
small and large trees of similar
the variation in seasonal elongation
understock effect. However, in ad­
genetic material seems to apply
also to the clonal understock which
est growth.
(r
=
Poorest growth was
0.80, d.f.
=
37), a highly sig­
nificant amount, was related to bud
dition to poor survival of grafts on
certain understock trees, survival of
favorable microclimate near the
ground. This difference between
has
consistently
burst
its
buds
bursting in 1956. Considerable mor­
tality occurred the second year, so
grafts of the three Portland trees
about ten days earlier than the
was
mature parent tree on the Oregon
only 32 scions were available for
Washington trees. This effect of the
the correlation in 1957. The rela­
scion types on second-year survival
Most clear-cut data are from the
tionship was highly significant, but
was statistically significant at the
only 38 percent of the variation in
length (r = 0.61, d.f. = 30) was
1-percent level.
Douglas-fir provenance study be­
gun in 1912 (6, 7) where 13 races
related to date of bud bursting.
nearly
double
that
of
the
Discussion
Elongation of natural branch
terminals was compared with elon­
gation of clone scion grafted to
The aim of the study, to deter­
mine the degree of genetic control
clone understock (clone grafts A,
bursting time in Douglas-fir, seems
to have been accomplished. Under
Fig. 1) to determine if grafting
itself caused a reduction in growth.
A definite reduction was noticed
the first year but little reduction
occurred during the second year.
This is evident when growth of the
single longest graft, A, is compared
with
growth
of
two
ungrafted
branches in the same relative posi­
tion on each of the five largest
clone trees :
Graft A
Ungrafted
branches
(Inches)
(Inches)
1956
6.7
8.3
1957
7.9
8.1
Growing
season
that can be shown for the bud
conditions of the experiment, the
several scion types burst buds at
consistently different times over the
2 years of the study. Relatively
small environmental differences
heightened the ability of this study
to show the genetic effect. Esti­
mates indicated that the genetic
component of total variation in
bud bursting time was very high
-94 and 96 percent.
Caution should be exercised in
drawing inferences from these high
figures for the genetic component.
For example, one might infer that
practically an variations in bud
State University campus.
follow about the same bursting or­
der in each plantation. In the 1912
study the same race began growth
in April at the lowest plantation
and in June at the highest, a two.
month delay due to environmental
differences.
In this study, reduction in growth
of the scions the first year after
grafting was expected. This poorer
growth, however, did not seem to
influence the order of bud bursting.
The relationship of increasing
growth rate with earliness of bud
bursting is at variance with other
studies that show little relation of
the two traits (1, 6, 7). However,
this relationship could be acciden­
tal since the slowest growing scions
were from the most northerly as
well as the most suppressed trees.
In addition, the clonal understock
and all scion types completed elon­
JULY1962
475
gation at the same time in late
June. Thus the late bursting scions
had a shorter growth period. This
apparent result of growth cessation
influenced by the understock tree
may not apply to ungrafted plants.
Understock condition contributed
far more than scion type to initial
survival of grafts.
Although this
pattern seemed related to vigor of
the individual clone tree, the rela­
tionship was not significant when
height was used as an indication
of vigor. In time, scion types also
showed great differences in sur­
vival. Again this appeared to re­
late to vigor of the scion parent
tree. Scions from open-grown trees
survived better and grew larger
than those from trees growing un­
ferent bud bursting dates onto
limbs of each of seven trees of a
much as two weeks.
17-year-old clone. The experiment
included replications of seven scion
rate only the first year. Relation­
types on each clone tree, the sev­
enth type being a control graft in
which a limb of the clonal tree was
cut, then regrafted.
The genetic component of the
bud bursting trait was estimated at
94 percent and 96 percent of total
variation for the two years of .ob­
servation. Thus, practically all
variation was genetic in the sense
that differences in bud bursting of
the seven scion t ypes were consist­
ent and little difference in this re­
gard was found between under­
stock trees.
netically similar material for as
Grafting depressed the growth
ships
1. !RGENS·MOLLER,
2.
3.
4.
tion. However, no valid statistical
test was possible whereby tree vigor
l ­
minimizing environmental infu
ences on bud bursting insofar as
5.
could be related to survival and
growth after grafting.
was possible. The study thus serves
as an example of the need for cau­
tion in using such estimates except
The degree of genetic control
over bud bursting in Douglas-fir
was investigated by grafting scions
from trees with known widely dif­
the study indicate that local en­
vironmental differences may con­
sistently delay bud bursting of ge­
between
Literature Cited
These high estimates of the ge­
netic component were obtained by
with natural or isolated cultured
populations, since other data from
investigated
of both parent tree and understock.
der crowded conditions in a planta..
Summary
were
survival of grafts and growth rate
HELGE. 1957. Eco­
typie response to temperature and
photoperiod in Douglas-fir.
Forest
Sci. 3: 79·83. Illus.
KENNEDY, R. W. 1961. Variation and
periodicity of summerwood in aome
second-growth Douglas-fir,
TAPP!
44:161-166. Illus.
LARSON, P. R. 1960. A physiological
consideration of the springwood-sum­
merwood transition in red pine. For­
est Sei. 6: 110-122.
LusH, JAY L. 1948. The genetics of populations. Iowa State College. 381 pp. (Processed.)
McCuLLOCH, W. F. 1943. Field snr­
vival
of
vegetatively
propagated Douglas-fir. Jour. Forestry 41:211­
212.
6. MORRIS, WILLIAM G., R. R. SILEN,
7.
and H. WENS·MOLLER. 1957. Con·
sistency of bud bursting in Douglas­
:fir. Jour. Forestry 55:208-210. IllU&
MUNGER., THORNTON T., and WILLI,UI
G. MORRIS. 1936. Growth of Douglas
fir trees of known seed source. U. B.
Dept. Agrie. Tech. Bui. 537. 40 pp.
DJus.
PRESENTATION OF SERVICE AwAJID.-John w. Smith, president, Seaboard Air Line
Railroad Company, was honored May 8 during a Seaboard sponsored forestry
field demonstration meeting by the U. 8. Forest Service when the company was
cited for 25 years of outstanding service in the field of forestry development­
t-he first railroad to be so honored. Shown above, left to right: Congressman J.
Vaughan Gary of Richmond, Va.; Edward P. Cli1f, chief forester. U.S. Forest Service,
Washington, D. C.; Mr. Smith; and the principal speaker, Charles B. Stauffacher,
executive vice president, Continental Can Company, Inc., New York City. More than
700 attended the forestry field meeting in Chesterfield County, Virginia, which in­
cluded the running of a special train from Washington, D. C., to the demonstration
area jnsi south of Richmond. Aboard the special train were 33 Members of Congress
representing 13 states, and 245 bwrl..ness, industrial and government leaders from
the northeastern section of the nation. The over-all program was under the direction of
the Seaboard's general forestry agent, Robert N. Hoskins.