Roy R. Silen
Donald L. Copes Douglas-fir
Seed Orchard Problems
-A Progress Report
THE AUTHORS are principal .plant genetkist and plant geneticist
respectively, Forestry Sci. Lab., Pac. NW 'Forest and Range
Exp. Sta., U.S. Forest Serv., Corvallis, Ore.
.•
ABSTRACT-In the mid-1960's, the problems of graft in­
compatibility, pollen contamination and slow and cyclic
seed production caused Douglas-fir seed orchards to lose
favor. Solutions now appear practical to graft incompati­
.-ri
1f
.
bility through providing con1patible rootstocks and to pol­
Jen contamination through delaying fioral bud development
With Wafer spray applications. The problem of slow and
cyclic seed, production is still unsolved.
determined that a wounding and rehealing phenomenon
Recent
solutions to two perplexing problems of
Douglas-fir seed orchards provide an excellent opportu­
nity to bring foresters interested in seed orchard tech­
nique up to date. Douglas-fir has had more seed orchard
problems than other important tree species. First, graft
incompatibility caused 30 to 60 percent of all Douglas­
fir grafts to die. Second, the Douglas-fir region has few
seed orchard locations that are free of serious pollen
contamination from the omnipresent native stands.
Third, Douglas-fir requires a number of years after
grafting before abundant cones are produced, and even
then heavy crop years are erratic. These three problems
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JI
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severely hindered successful seed orchard establish­
ment. Reluctance to establish additional seed orchards
was so strong through the mid-1960's that a tree
improvement program which avoided establishing seed
orchards gained prominence (23). Nonetheless, the
three problems were given high research priority be­
cause seed orchards are an indispensable part of most
long-term breeding programs. This report documents
the research attack on each problem.
Graft Incompatibility
Douglas-fir is easily grafted; a good technician will
have little difficulty in obtaining 90 percent success if
he grafts at the proper time in the spring. As with heart
transplants in humans, problems develop later. Between
1958 and 1963 seed orchardists began to suspect latent
troubles with Douglas-fir grafts ( 6). Many grafts that
had appeared normal for up to seven years developed
swellings at the union and died. By 1964 the problem
had become so serious that seed orchardists urged that
a scientist work full-time on the problem. The junior
MARCH 1972
author was assigned this investigation in 1965.
Initially, all of the incompatibility theories-poor
grafting technique, mechanical weakness at the graft
union, lack of rootstock limbs close to the union,
differential growth rates of stock and scion, virus infec­
tion or biochemical antagonism-had to be considered.
As a result of early research (J, 2) all but biochemical
antagonism and virus infection have now been elimi­
nated as reasonable causes of graft incompatibility.
The first major breakthrough came when it was
was associated with incompatibility. This phenomenon
occurred unfailingly each spring as new cambial growth
began. The wounding never occurred in compatible
grafts or where the plant was grafted back upon itself
(2). In 1967 Copes suggested a practical solution
involving two grafts of a parent tree per rootstock. One
graft could be cut off 15 to 18 months after grafting and
examined ·microscopically for wound areas. If the in­
compatibility symptom were not found, the rootstock­
scion combination would be compatible and the re­
maining graft left in the orchard for seed production.
But if the incompatability symptom were present in the
sacrificed graft, the remaining graft would be rogued
and grafts of another plant tested at that orchard
position (1). This usually results in orchards with
unequal numbers of grafts per parent.
A refinement of the method was added in 1968. It
'
was known that cuttings from adult Douglas-fir were
difficult to root but that seedlings rooted easily. By
testing compatibility of each parent on 10 to 20 juvenile
rootstocks, some compatible rootstocks could be located
for all highly incompatible parent trees. Once a com­
patible rootstock is found, adequate numbers of each
rootstock can easily be produced by rooting cuttings of
the juvenile rootstock (1). In this refinement, grafts of
all parents can be equally represented in the orchard.
Unfortunately, incompatibility will continue to be a
problem in older orchards which were established be­
fore evasion techniques became known. But in the new
seed orchards, the problem has changed from a major
threat to their existence to a minor problem which can
readily be controlled. Most seed orchardists are now
using the new evasion techniques.
145
Pollen Contamination
Before 1956 an isolation zone of a few hundred feet
surrounding an orchard ,was considered adequate pro­
. tection from contaminating pollen. Because Douglas-fir
pollen is relatively large, most of it was thought to fall
near the tree (24).
However, the first Northwest studies of Douglas-fir
pollen flight, conducted in 1956, revealed a serious
pollen contamination problem (16). So much pollen is
produced during a heavy year that virtually every cubic
inch of air over vast areas of the Northwest is loaded
with pollen. Most seed orchards have since been sam­
pled during heavy seed years to determine degree of
pollen contamination. Some orchards on flat land aver­
aged about 3,000 contaminating pollen grains per
square inch during the pollen season despite several
miles of isolation. Pollen contamination count reached
7,500 per square inch in orchards located in narrow,
forested valleys. Thus, isolation was ineffective against
pollen contamination.
During the 1958-66 period the senior author ex­
plored two other approaches to reducing pollen contam­
ination. The first hypothesis tested was that low­
elevation orchards containing grafts of high-elevation
plus-trees would be inherently delayed in bud develop­
ment and, thus, avoid serious contamination from the
surrounding stand. This approach was also ineffective
as there was great overlap in duration of pollen shed
between the local low-elevation stand and high­
elevation seed orchard trees (17).
The other approach involved mechanical and chemi­
cal removal of floral buds. The hope was to delay the
year of heavy cone production iu the orchard to the
following year when the surrounding native stands were
not producing in quantity. If this were possible, the
contamination problem would be .drastically reduced.
Following horticultural experience with apples (5),
female Douglas-fir buds were mechanically removed
with expectation of a better crop the next year. A better
crop did occur when female buds were removed before
a good seed year. Three cones were produced for each
female bud removed the previous year. A chemical
means of removing freshly burst cone buds was even
found. From among seven chemical thinning agents
commonly sprayed on fruit trees, only 2-4-D (0.2
percent) and urea fertilizer (1.0-percent solution) were
found safe and effective. However, this approach failed
when used during a good seed year. Only one cone was
produced the next year for every five cone buds re­
. moved.
Because of the seriousness of the contamination
problem, the Northwest Pollen Problems Committee
was formed in 1968. The Committee, composed of seed
orchardists and researchers, began by brainstorming
new approaches to the problem and then soliciting work
on the proposals. One proposal explored without suc­
cess was the trapping of pollen from the air on plastic
screens spraved with water or charged with electricity.
pollen problem. Instead, the senior author successfully
arrested reproductive bud development by cooling the
plants with a cold water spray. The spray technique
was tried first in 1968 using a commercial sprinkling
system at a U.S. Forest Service seed orchard near
Oakridge, Oregon. Spray periods of six, four and two
weeks prior to the normal period of pollen release were
used. Water from melting snow was sprayed whenever
air temperatures exceeded 50°F. Both the four- and
six-week treatments kept the buds of the orchard trees
closed well past the peak of local pollen release (20).
Similar spraying trials were repeated in 1969 at the
U.S. Forest Service seed orchard near Oakridge, Ore­
gon, and in 1970 by Pacific Logging Company, San­
nichton, British Columbia. All trails kept the floral buds
unopened through the major portion of the local pollen
flight period.
Horticultural research has recently demonstrated that
the ice water was not required for cooling because all
water droplets quickly approach wet bulb temperature
while falling through the air. Thus, water at normal
temperature appears useful iu cooling the buds. No
evidence of any damage to Douglas-fir trees, floral buds
or seeds resulted from the water treatment. The only
serious limitation appears to be a high capital invest­
ment in overhead sprinkling equipment. Pacific Logging
Company in British Columbia and Weyerhaeuser Com­
pany at Centralia, Washington and Jefferson, Oregon
feel the cost is justified if frost protection benefits are
also obtained. Each is now expanding its trials to
operational scale within its seed orchards. Unless un­
foreseen developments occur, a simple, though expen­
sive, first solution to the pollen contamination problem
has apparently been found.
Flowering Problem
Unfortunately, similar success has not been achieved
with problems of delayed and cyclic cone production.
The problem once appeared solved by fertilizer appli­
cations. Beginning about 1954, considerable enhance­
ment of cone production resulted from applying fertil­
izer to wild-grown trees ·( 2 I) and, to a lesser extent, in
seed orchards. However, since tben, regular applica­
tions of fertilizers have had little influence on the cyclic
pattern of good and poor seed years. Good crops are
usually improved but poor ones are hardly affected;
however, it still is the only technique widely employed
to influence Douglas-fir cone crops.
Other studies have centered on cone bud develop­
ment, floral initiation and cultural treatments. Cone bud
development studies were aimed initially at providing
ways to predict future cone crops. The finding that male
and female cone bud production was highly correlated
provided a means for extending predictions from 12 to
16 months ahead of seedfall (18). Other studies of
histochemical stains on bud primordia provided indica­
tors that made even earlier predictions possible (11).
These techniques were tested by Weyerhaeuser re­
An important spinoff of bud development studies was
searchers in Centralia, Washington and in our Corvallis
laboratory.
Another Committee proposal was to wash foreign
the realization that most irregular cone production in
Douglas-fir resulis not from variations in floral initia­
pollen from the air with a water spray. This was not
directly tested but did learn to the first solution to the
146
tion but from variations in subsequent floral develop­
ment (18). This observation has been confirmed by
Owens (11, I 2) and Ebel! (7) for Douglas-fir and by
JOURNAL OF FORESTRY
(' .. -
Eis
(8)
for two species of
Abies. The time at which
potential cone buds are initiated in Douglas-fir can be
pinpointed. However, at that time, the bud type appar­
ently has not been determined. Newly initiated buds can
•,develop along any of five pathways: they can abort
duction can be understood and precise timing of hormo­
nal or other treatments can be made
partially develop, then become latent undetermined buds
quent year; or they can fully develop into vegetative,
cone, or pollen-cone buds. This development pathway
is determined some time during the first I 0 weeks fol­
lowing initiation
(JJ).
The exact time has not yet been
determined. Potentiaily good crops frequently abort dur­
ing this period.
Correlations between -weather records and cone crops suggest that various "'eather patterns in the two growing
Conclusions
Status of work on the three major
(10,
22).
(3)
Ching and Lavender
have applied
favorable climatic patterns and also provided one addi­
tional growth cycle per year to seedlings but have not
down and one to go." If present methods of evading
graft incompatibility and pollen contamination continue
to cause no serious side effects, more research effort can
be directed to delayed and cyclic cone crops. The large
backlog of information accumulating on floral initiation
and cone-bud development
solution
found.
or
2.
enhanced floral bud numbers, attributing this to contin­
3.
stimulated
flowering.
Ebell
demonstrated
drought in the early part of the growing season greatly
ued floral development rather than actual floral initia­
tion
(7).
Silen
(18)
noted
that
bud
development
appeared to halt through the Douglas-fir region about
.
./
the sarne date in 1964 and suggested that some broad
nvironmental event, as yet undetermined, was respon­
sible. Studies on cooling, warming, debudding, defoliat­
ing, shading and girdling •were made in an effort to
identify the factor. Treatments ranging in duration from JO to 30 days at any time in the growing season have
altered the normal male and female bud numbers up to
30 months ahead of seedfall
(19).
But none of these studies has yet pinpointed a single
environmental event as being capable of widespread
halting of floral bud development. As if to increase the
research challenge, it appears from a]] this that a host
of environmental factors can influence floral develop­
ment at almost any time in the three growing seasons
ahead of seed 'all.
Meanwhile, physiological studies concerning hormon­
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
al control of floral bud initiatio·n in other conifers are
progressing rapidly and to great depth. A landmark
14.
discovery was the use of a gibberellin for initiation of
floral buds in Cryptomeria reported by Kato and co­
raises
the
hope
that
a
another evasion of this problem may soon be
Literature Cited
1.
that
yet
problems of
Douglas-fir seed orchards can be expressed as "two
seasons prior to bud differentiation can influence cone
crops
Work is
tional requirements _for cone development . _
within a few weeks and completely disappear; they can
which may later develop as vegetative buds in a subse­
(11, 12).
progressing rapidly on all fronts except that 9f nutri­
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Douglas-fir seed orchards. Western Reforestation Coordinating
Comm. Proc. 1968: 19-22.
1970. Initiation and development of graft incom­
patibility symptoms in Douglas-fir. Silvae Genet. 19(2-3) : 101107.
CHING, K. K.. and D. P. LAVENDER. 1970. Effects of certain
controlled environments upon incidence of precocious flower­
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seedlings. (Abstr.) First N. Amer. Forest Biol. Workshop,
Mich. State Univ., East Lansing.
CROZIER, A.. C. c. Kuo, R. C. DURLEY. and R. P. PHARIS. 1970.
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'
DAVIS, L. D. 1957. Flowering and alternate bearing. Amer.
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DUFFIELfJ, J. W., and J. G. WHEAT. 1964. Graft failures in
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ERELL, LORNE F. 1970. Physiology and biochemistry of flower­
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ual Reproduction Forest Trees, Varparanta, Finland. 10 p.
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Abies lasiocarpa and A. grandis. Can. J. Bot. 48 :141-143. illus.
KATO. Y., N. FUKUHARA, and R. KOBAYAS H I. 1958. Stimulation
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2nd Meeting Japan Gibberellin Res. Assoc., p. 67-68.
L OWRY, WILLIAM P. 1966. Apparent meteorological require­
ments for abundant cone crop in Douglas-fir. Forest Sci.
12(2):185-192.
OWENS, JOHN N. 1967. A new look at Douglas-fir cone devel­
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Assoc., Portland, Ore., p. 10-12.
. 1969. The relative importance of initiation and
early development on cone production in Douglas-fir. Can. J.
Bot. 47: 1039-1049. illus.
PHARIS, R. P .. w. MoRF. and J. N. OWENS. 1969. Development
of the gibberellin-induced ovulate strobilus of western red
short day
cedar: quantitative requirement for long day
long day. Can. J. Bot. 47 :415-420, illus.
and WILLIAM MoRF. 1967. Experiments on the
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Bot. 45:1519-1524, illus.
in Victoria has shown that certain mern.bers of the
15.
and JoHN N. OWENS. 1966. Hormonal induction of
flc•wering in conifers. Yale Sci. Mag. Nov., 4 p.. illus.
16. SILEN, ROY R. 1962. Pollen dispersal considerations for Doug­
las-fir. J. Forestry 60: 790-795, illus.
17. -----. 1963. Effect of altitude on factors of po::en con­
response to gibberellin treatment. They also demon­
18.
workers in
1958
(9).
A Canadian research group
headed by Pharis in Calgary and supported by Owens
Cypress family initiate cones at a very young age in
strated that the sex of cone-bud formed can be con­
trolled by altering the day length under which cones
develop
(13,
14, 15). These promising results must be
tempered somewhat since.similar treatments have yet to
19.
20.
work in Douglas-fir or other members of the Pinaceae.
tamination of Douglas-fir seed orchards. J. Forestry 61: 281283, illus.
1967. Earlier forecasting of Douglas-fir cone
using male buds. ,J. Forestry 6502):888-892, illus.
-----. 1967. How early can Douglas-fir cone crops be
dicted. Western Reforest. Coordinating Comm,, Western
estry & Conserv. Assoc. Proc., p. 12-18, illus.
and GENE KEANE. 1969. Cooling a Douglas-fir
21. STOATE. T. N.,
to determine the native gibberellins and other hormones
22.
present
(13)
(4), as well as nutritional
(7)
and day-length
requirements necessary for cone development.
Normal patterns of cone formation must also be de­
scribed before environmental influences on cone proReprinted
from
2::i.
24.
pre­
For­
seed
orchard to avoid pollen contamination. Pacific Northwest
Forest and Range Exp. Sta. USDA Forest Serv. Res. Note
101, 10 p.
Further work is in progress using conifers which do not
readily respond to this treatment. This includes studies
crop
L
MAHOOD, and E. C. CROSSIN. 1961. Cone pro­
duction in Douglas-fir (Pseudotsu_qa menzicsii). Empire For­
est. Rev. 40(2): 104-110.
VAN VRf DENRURCH. CAREL L. H . . and J. G. A. LA BAsTrnE.
1969. The influence of meteorological factors on the cone crop
of Douglas-fir in the Netherlands. Silvae Genet. 18(5-6):182186.
WHEAT. JOSEPH W. 1969. Forest tree improvement work ad­
vances in Douglas-fir region. Forest Ind. 96(5) :38-40, illus.
WRIGHT, JON"ATHAN W. 1953. Pollen dispersion studies: some
practical applications. J. Forestry 51: 114-118.
the JOURNAL OF FORESTRY, Vol. 70,
No.
Purcha sed by USDA F·orest Scr\·iee for offl..cial
3, March 1972
use.
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