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Figure
1 (left). Red Oaks started in Spin-out treated #40
DeePots February 2001. The same system was used
to germinate the chestnuts.
Figure
2 (right).
Chestnut
trees were transported into the field in Spring
2000. |
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INTRODUCTION
The American chestnut (Castanea dentata Marsh. Borkhausen) once
made up one-third of northeastern U.S. forests. Today most chestnut
trees in the United States are little more than stumps that
sprout and occasionally flower, but rarely produce fruit. In
one of many efforts to change the future of the American chestnut
and return it to its glory in the landscape and wood-lots of
Pennsylvania, the Pennsylvania
Chapter of the American Chestnut Foundation (PC-TACF) has
been acquiring seed from the American Chestnut Foundation initiated
back-cross breeding program to produce blight-resistant American
chestnuts. A successful breeding and disease-screening program
requires that all possible progeny representing the crosses
survives and can be screened. The PC-TACF’s approach to
seed germination and seedling production relied exclusively
on field planting of seeds in the fall allowing natural stratification
and germination or direct seeding in the spring after controlled
stratification. This approach resulted in fewer seedlings surviving
than desired due to animal and insect predation and soil pathogens.
Poor seed germination combined with the wildlife predation of
seedlings and the five to eight-year growth period required
for a tree to reach sexual maturity limited the effectiveness
of the breeding and screening program. In late fall of 1998,
the ornamentals research group at the Pennsylvania
State University Horticulture Department initiated a partnership
with the PC-TACF to develop an accelerated growth production
system to bypass the problems listed above. The accelerated
growth system consisted of stratifying the seeds following collection
in the fall at 41F in moist peat; planting into Deep pots in
late winter under greenhouse conditions; and transplanting the
seedlings into larger containers or directly into the field
in late May.
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Figure
2. Three year old Amercan Chestnuts started from seed,
in Spin-out treated containers in the greenhouse.
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Figure
3. Two year old American Chinese BC3 hybrid plantation.
Seedlings were transplanted to the field in June of
the same year.
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DESCRIPTION OF THE PROCESS
First Planting Trial:
A seed population of 120 American Chestnut seeds, representing
six seed lots, were received in mid October, 1998 and placed
by lot number in zip-lock bags filled with moist peat moss.
The bags were stratified at 41F in a walk-in cooler.
The seeds were stratified for 19 weeks (until the first week
of March, 1999) after which they were planted into Spin-out®
(Griffin LLC., Valdosta, GA) treated #40 Deepots™ (Stuewe
and Sons, Inc., Corvallis, OR.) filled with Sunshine #4 (Fisons
Horticulture Inc., Vancouver, B.C.) potting medium, and placed
on benches in the greenhouse. Germination occurred within
14 days among the seed lots. During the first month, plants
were fertilized twice weekly with 60 parts per million (ppm)
nitrogen (N) in the form of Peters 21-7-7 (including micronutrients)
after which the rates were increased to 90 ppm N.
The seedlings were transplanted into 3 gallon Spin-out®
treated pots containing Fafard #52 (Fafard Inc., Agawam, MA)
and placed under 70% shade at the Horticulture Research Farm
in Rock Springs, PA. Plants were irrigated three times at
15-minute intervals in the early morning through an overhead
intermittent spray system. Plants were top-dressed with 53
grams of Sierra 17-6-10 plus micronutrients (Scotts-Sierra
Horticultural Products Co., Marysville, OH) in early June.
A granular preemergence herbicide, Ronstar 2G (oxadiazon)
(Aventis CropScience, Research Triangle, NC) was applied to
the containers at 2.6 lbs active ingredient per acre (a.i/A)
on June 19.
Plants were prepared for over-wintering in late November by
watering the pots to saturation. Before covering, rodent control
consisting of zinc phosphide treated grain was placed in one
foot long, 3 and 4" diameter PVC pipes to reduce rodent
damage to tree trunks. Plants were laid on their side and
covered with a Cady Bag (Cady Bag Co., Inc., Atlanta, GA.)
over-wintering blanket. Sixteen seeds and seedlings did not
survive from the original 120 seeds acquired due to non-germination
or loss during over-wintering. 104 plants were uncovered and
righted 13 weeks later (late February 2000).
On June 21, 2000, the 104 trees were divided into two lots
with 21 trees being delivered to a campus planting while 83
trees were transplanted into a retired apple orchard at the
Pennsylvania
State University Horticulture Farm in Rock Springs, PA.
Planting holes were drilled with a tractor-mounted auger at
ten-foot on center spacing. Trees were removed from their
pots and manually planted and were thoroughly watered in by
an evening thunderstorm. Even though there was very little
rainfall over the growing season, no supplemental irrigation
was applied. A fall herbicide treatment consisting of Roundup
Pro™ 4L (glyphosate) (Monsanto, St. Louis, MO) at 1.5
lbs (a.i./A) and Princep 4L (simazine) (Syngenta Crop Protection,
Inc., Greensboro, NC) at 1 lbs. a.i./A, was applied on November
3, 2000. A spring preemergence treatment Pennant 7.8 EC (metolachlor)
(Syngenta Crop Protection, Inc., Greensboro, NC) at 3 lbs.
a.i./A was applied on April 10, 2001.
Second Planting Trial:
The stratification process was repeated in the fall of 1999
with a second seed lot containing 1181 American/Chinese hybrid
BC3 nuts from 16 different lines. Also included was a set
of checks consisting of 22, 15 and 16 nuts from American,
Chinese, and F-1 back-cross hybrid lines, respectively. In
late February 2000, the nuts were planted in Spin-out®
treated #40 Deepots™ in Fafard #52 media and fertilized
with Sierra 17-6-10 w/ minors (8-9 month formulation) at 1
teaspoon per pot. On April 25 the plants were moved to a shaded
hoop house with overhead irrigation.
A second chestnut plantation was established on a Murrill
Channery silt loam soil and protected from deer by electric
fencing. The plantation spacing was six feet between rows
and five feet within the rows. 1162 seedlings were transplanted
in mid May 2000 in a randomized complete design. A portable
gas operated auger was used to drill the holes for planting.
All plants from the individual seedlots were randomized prior
to planting. The preemergence herbicides Princep 4L at 2.5
lb a.i./A and Surflan AS (oryzalin) (Dow AgroSciences, Indianapolis,
IN) at 2 lb a.i./A were applied on June 2.
Rainfall was minimal after the herbicide treatments, which
resulted in heavy weed populations within the plantation.
On June 21, each plant was hand irrigated with one quart of
water. Very little rainfall occurred the rest of the growing
season. By the first week of August the annual grasses, especially
green foxtail had taken over the plantation. The grasses were
treated with Fusilade II 2L (fluazifop-p-butyl) (Syngenta
Crop Protection, Inc., Greensboro, NC) at 0.375 lbs ai/A.
A fall herbicide treatment of Roundup Pro™ and Princep,
both at 1 lb a.i./A, was applied as a directed spray on November
3, 2000. A spring preemergence treatment of Pennant was applied
on April 10, 2001.
OBSERVATIONS
First Planting Trial
A (86%) survival rate was recorded from seed acquisition through
the first winter for the American chestnut seeds. Only three
plants were lost over the next two growing seasons due to
deer damage resulting in a 84% overall survival and a 96%
field planting survival rate. Two of the plants flowered and
set seed in the fall of 2000, two years after germination.
Second Planting Trial
A 98% germination and survival rate was recorded among the
American/Chinese BC3 and check seeds. The two-year survival
rate in the field for these seedlings is 88%. Two observed
problems that were encountered during this trial involved
the acclimation of the seedling to field conditions. On some
of the leaves of the seedlings a distinct bleaching occurred
this may have been due to a limited cuticular wax deposition
on the leaf surface prior to moving to the field. Extending
the acclimation period may reduce this problem. The second
observation was that a majority of the seedlings exhibited
marginal leaf scorch and a subsequent slowed growth once transplanted
to the field from either Deepot tubes or three-gallon pots.
The leaf scorch was more pronounced among the seedlings transplanted
from the Deepot tubes compared to seedlings transplanted from
3-gallon pots. The marginal leaf scorch occurred whether the
seedlings were immediately exposed to field light levels and
prevailing wind conditions or moved and maintained under the
protection of shade cloth within a hoop house for several
days prior to planting to the field. One obvious difference
between the Deepot and 3-gallon seedlings which may have lended
to the difference in leaf scorch was the limited amount of
medium surrounding the rootball of the Deepot seedlings compared
to the seedlings in the 3-gallon pots. Soilless medium has
a limited capacity for holding moisture and under field conditions
the Deepot seedlings will be more likely to experience drought
stress. Dry soil conditions surrounding the root ball will
further assist in the dessication of the seedling.
CONCLUSIONS
The accelerated growth system can be successfully used in
chestnut seed propagation.
FUTURE PLANS
After the trees develop a caliper of 1.5” the two chestnut
plantations will be screened with Cryphonectria parasitica
to determine their resistance. Survivors can be utilized in
future chestnut blight resistance breeding work.
This work on the use of accelerated growth to aid in the germination
and survival of difficult to propagate native trees and shrubs
will continue with other genera. Further studies on the acclimation
procedure will be conducted to reduce marginal leaf scorch
in the field after transplanting. One approach to be tested
includes applying forced air across the seedling canopies
to harden off the leaf and increase cuticular wax deposition
prior to transplanting. A second approach will involve planting
seedlings from 3-gallon pots into the field prior to bud break.
A third approach to be tested will involve planting seedlings
from Deepot tubes into soil beds for one season after which
they will be harvested as dormant bareroot liners and planted
to the field
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