New Forests 3: 21-30 (1989)
Publishers. Printed in the Netherlands
© 1989 Kluwer Academic
Softwood cuttings for propagation of red alder
M.
A
RADWAN, T.
A
MAX and D. W. JOHNSON
United States Department of Agriculture, Forest Service, Forestry Sciences Laboratory
Olympia, WA 98502, and Forestry Sciences Laboratory, Portland, OR 97208, USA
Received 26 May 1988; revised and accepted 16 January 1989
Key words: epicormic sprouts, terminal and nonterminal cuttings, indole-3-butyric acid,
vegetative propagation, Alnus rubra
Results show that red alder can be propagated by using softwood cuttings from
shoots of young trees and epicormic sprouts of older individuals, especially when IBA is
employed. Use of epicormic sprouts from mature trees of proven performance will allow
propagation of presumably superior trees. The ortets will be used only once. Resulting
plants can be outplanted in a clonal nursery, and more cuttings can be obtained from the
plants after an establishment period of about 2 years. The nursery then can supply planting
stock for establishing new plantations with presumably superior trees.
Application.
Tests were conducted to assess rootability of red alder softwood cuttings from
shoots of young trees and epicormic sprouts of mature individuals. Ortets were 3 to 34
years old, and treatments with and without indole-3-butyric acid (IBA) were compared. The
extent of rooting and root vigor on the cuttings varied greatly among ortets and treatments.
Among nonterminal cuttings, the best overall rooting success, with and without IBA, was
obtained with cuttings of the youngest ortet. Average rooting of terminal and nonterminal
cuttings of one clone were 100% and 64%, respectively. Although cuttings of some trees
rooted well without IBA, the IBA treatment appeared to be generally beneficial. For all
nonterminal cuttings of all clones, best results (80.0%) were obtained with a 10-sec dip in
2,000 or 4,000 ppm IBA. Vigorous planting stock was obtained from the rooted cuttings of
all clones. Using epicormic sprouts from mature trees of proven performance will pre­
sumably allow propagation of superior trees and establishment of new plantations with
improved stock.
Abstract.
Introduction
Vegetative propagation of red alder (Alnus rubra Bong.) offers the
advantage of cloning superior trees in a relatively short time (Hartmann
and Kester 1983). If successful, the technique will be desirable for both
experimental work and forestry practice, especially in developing bio­
energy plantations. The species is now considered a principal candidate
for developing such plantations in the northwestern United States where it
is the major hardwood tree.
22
Little information exists about propagating red alder from cuttings. In a
small test, Monaco and others (1980) succeeded in rooting "greenwood"
cuttings of red alder with and without treatment with indole-3-butyric acid
(IBA), but they used young (1-2 years), greenhouse-grown ortets. In a
more recent study, Carpenter and others (1984) used 8,000 ppm IBA
according to methods by Monaco and others (1980) to root "new green
stem" cuttings taken from 4- to 5-year-old red alder saplings. The authors
obtained enough rooted cuttings for their experiment, but they did not
report any measure of rooting success. There are no literature reports on
rooting of red alder cuttings made from epicormic sprouts or other parts
taken from older trees. Epicormic basal sprouts from mature trees of
European alder (Alnus glutinosa (L.) Gaertn.), however, were successfully
rooted in France (Martin and Guillot 1982).
Our study was designed to compare the rootability of "softwood"
(succulent new spring growth) cuttings of 7 different red alder clones; our
preliminary experiments showed that year-old "hardwood" (mature dor­
mant hardwood) cuttings of red alder were difficult to root. Cuttings were
taken from shoots of young trees and epicormic sprouts of older individ­
uals. Epicormic sprouts are desirable because
they are easily accessible, apparently juvenile shoots that may root
easily (Martin and Guillot 1982, Hartmann and Kester 1983), and
they can be obtained from older trees of proven performance, and thus
make possible propagation of superior trees.
Materials and methods
The ortets and cuttings
Cuttings were prepared from current year's epicormic sprouts and soft­
wood shoots. Four mature trees ( > 25 years) were used as ortets for the
epicormic sprouts, and three much younger trees ( < 7 years) were used as
ortets for the shoots. Selection of the mature trees was based on
superiority in important characteristics manifested, such as fast growth,
straight boles, and few lower branches. The young trees were too young
for selection by desirable traits. These trees differed mainly in age and
location; they were included in the study primarily to compare rootability
of their shoots with that of the epicormic sprouts of the older trees. All
trees were located in different natural stands about 10 km south of
Olympia in western Washington, where many natural stands of red alder
occur.
In January 1986, the ortets were released from shading by shrubs and
23
other trees, and each tree was fertilized with 2 kg of a 10-20-20 commer­
cial fertilizer. The mature trees were girdled around half the circumference
at several points along the bole to encourage formation of epicormic
sprouts, and the younger trees were heavily pruned to stimulate produc­
tion of vigorous new shoots. Ages and diameters of the stock trees are
shown in Table 1. New shoots and epicormic sprouts were harvested on
July 14, 1986. Cuttings made from the shoots were 10-12 em long and
2-4 mm in diameter. Cuttings made from the epicormic sprouts were
6-10 em long and 2-3 mm in diameter. One-half of the cuttings of tree
12 were prepared so that each cutting included the terminal bud and the
small terminal leaves. Remaining cuttings of tree 12 and all cuttings of the
other stock trees were prepared so that the terminal 2- to 3-cm portions
of the shoots and sprouts, including the terminal buds, were cut and
discarded. The experiment therefore included a comparison of terminal
and nonterminal cuttings taken from one of the test trees. All cuttings had
a minimum of one-half leaf and one axillary bud. Presence of leaf material
on cuttings has been shown to increase their rootability (Hartmann and
Kester 1983).
The chemical treatments
Treatments tested were: control (water dip); 2,000 ppm IBA, 1O-see dip;
2,000 ppm IBA, 15-sec dip; 4,000 ppm IBA, 10-sec dip; and 4,000 ppm
IBA, 15-sec dip. The IBA treatments were based on results of earlier
experiments with red alder (Radwan and others 1986). The IBA solutions
were prepared by dissolving the acid in a small amount of absolute
ethanol and diluting the solution with water to a final concentration of
50% ethanol. Earlier experiments (Radwan and others 1986) showed this
method of preparation was much easier than that used by Monaco and
others (1980). The pH of the JBA solutions was about 4.5.
Table I.
Characteristics of the red alder ortets.
Trees used to produce epicormic sprouts
Tree J.D.
number
2
3
5
10
(yr)
Diameter at
breast height
(em)
34
27
27
28
27.0
23.7
26.8
21.6
Age
Trees used to produce shoots
Tree J.D.
number
Age
(yr)
II
5
12
13
6
3
Diameter at
breast height
(em)
5.6
7.2
24
Treatment consisted of dipping 2-3 em of the basal ends of the
cuttings in the appropriate solution for the specified time. There were 5
cuttings of each clone per treatment and a total of 200 cuttings for the
entire experiment. Cuttings were labeled with plastic tags indicating the
ortet, treatment, and cutting number.
Cuttings were inserted 2-4 em into a moist rooting mixture of
vermiculite and perlite (1:1 v/v) placed in the bottom of a mist chamber.
The chamber was about 2.5 m long X 1.5 m wide X 1.0 m high. All sides
of the chamber, except the bottom, were covered with 5-mil Mylar 1 sheet
film to allow for maximum light penetration. Cuttings were randomly
placed in the chamber in 200 marked positions. The chamber was
maintained at 25 ± 2 ·c during the day and night and was provided with
intermittent overhead mist of a 24-sec spray per hour during the day. A
bank of Growlux 1 fluorescent lights supplemented natural light in early
morning hours and extended the photoperiod in the evening to a total of
16 hours. Rooting data were collected at 28, 42, and 62 days from the
start of the experiment. A cutting was considered rooted if it had a
minimum of two 3-mm long roots.
Production and establishment of new plants from rooted cuttings
The rooted cuttings were transplanted into deep narrow pots containing a
mixture of vermiculite, perlite, and Tumwater sandy loam (1:1:1 v/v/v).
The young plants were kept in a greenhouse for 5 weeks. During that time,
the photoperiod was maintained at 16 hours, the temperature was about
21 ·c during the day and 15 ·c at night, and the plants were periodically
fertilized with full-strength Hoagland solution # 1 (Hoagland and Arnon
1950). The plants were then moved to a plant growth chamber and
allowed to harden off gradually. At the end of January 1987, the plants
were moved to a cold room (ca. 2 •q and stored there during the winter.
In May 1987, the dormant planting stock was outplanted at 1- X 1-m
spacing in a fenced enclosure at our laboratory, and the plants were
tended as required during the 1987 growing season.
Statistical analysis
Cumulative rooting data after 62 days were analyzed by procedures
specifically designed for experiments where the response variable is
categorical (Grizzle and others 1969); factors tested in the analysis were
clones, treatments, and clone X treatment interaction. Standard errors
were also calculated to indicate the magnitude of error associated with
each estimated percentage.
25
Results and discussion
Response of the ortets to pruning and girdling
Pruning induced all young trees to produce numerous, healthy shoots. In
contrast, production of epicormic sprouts in response to girdling differed
among the older trees; trees 5 and 10 produced more sprouts than the
other two trees, but reasons for the difference were not apparent. The
sprouts appeared all along the bole in the vicinity of the girdles, up to 4.5
m high. They varied in vigor and length within and among the stock trees,
but no consistent pattern emerged. In general, the sprouts (Fig. 1) were
mostly yellowish green and lacked the vigor shown by the shoots of the
Fig. 1. Epicormic sprouts formed on trunk of tree 2.
26
young trees in spite of releasing and fertilizing the trees before girdling.
The girdled trees themselves also appeared to have been weakened by
girdling; their foliage was yellow green compared with the green foliage of
the neighboring ungirdled trees.
Rooting of the cuttings
In general, very little rooting of any cutting occurred before the first 20
days in the mist chamber. By 28 days, up to 100% of the cuttings of some
treatments had rooted; rooting in the other treatments continued through
62 days when the experiment ended. The extent of rooting and root vigor
on the cuttings also varied among clones and treatments. In general, roots
produced by cuttings from young trees were more numerous and vigorous
than those produced by cuttings from old trees. Rooted nonterminal and
terminal cuttings are shown in Fig. 2.
Fig. 2. Rooted nonterminal (left) and terminal (right) red alder cuttings.
27
The cumulative rooting percentages by clone and treatment are sum­
marized in Table 2. In spite of some apparent differences among some of
the values presented, statistical analysis of the data according to Grizzle
and others (1969) did not detect any significant differences ( a= 0.05) for
clone, treatment, or clone X treatment interaction. This resulted mainly
from the design of the experiment where we tested a relatively large
number of treatment combinations (i.e., 3 5) using a small number of
cuttings per treatment (i.e., 5). Under these conditions, the statistical test
Table 2.
Rooting percentages (SE) of red alder cuttings after 62 days.
Treatmentb
Clone
number"
A
c
B
D
E
Average
Mature trees
2
60
80
40
(22)
(18)
(22)
20
40
(18)
(22)
60
100
3
5
(22)
10
(
-)
80
80
(18)
(18)
100
72
80
-)
(18)
20
60
40
36
(18)
(22)
(22)
(10)
80
80
84
(18)
(18)
(
100
(
-)
100
(
-)
100
(
(9)
(7)
92
100
-)
(
-)
(12)
Young trees
20
60
60
80
60
56
(18)
(22)
(22)
(18)
(22)
(10)
11
12
100
60
(
(22)
13
100
100
(
Average
12P
-)
(
-)
80
40
40
64
(18)
(22)
(22)
(10)
100
(
-)
100
(
100
-)
(
-)
57.1
80.0
71.4
80.0
71.4
(8)
(7)
(8)
(7)
(8)
100
100
(
-)
(- )
-)
100
(
-)
100
(
100
-)
(-)
100
(
-)
100
(
-)
" Cuttings of clones 2, 3, 5, and 10 were made from epicormic sprouts, and cuttings of clones 11, 12, and 13 were made from shoots. T
terminal cuttings; all others were nonterminal. b
A
=
untreated control; B
=
2,000 ppm IBA, 15-sec dip; D
2,000 ppm indole-3-butyric acid (IBA), 10-sec dip; C
=
4,000 ppm IBA, 10-sec dip; E
=
=
4,000 ppm IBA, 15-sec dip. ' Data from treatment 12T were not included in the statistical analysis because clone 12 was the only clone in the experiment with terminal and nonterminal cuttings. 28
was not sensitive enough to detect possible differences among the 35
rooting percentages (i.e., 7 clones X 5 treatments); note the large standard
errors associated with many of the values primarily resulting from small
sample sizes. Guidelines in the literature (SAS Institute 1985) suggest that
our experiment would have been better designed for the statistical test
employed had we used 25 cuttings per treatment and 875 cuttings for the
entire test (i.e., 7 clones X 5 treatments X 25 cuttings per treatment). This
was impossible because of the limited capacity of the mist chamber and
the very limited number of cuttings from some stock trees.
Some apparent differences between treatments and clones, while not
established statistically, may be important and deserve further considera­
tion. For example, the data show that among nonterminal cuttings, the
best overall rooting success, with and without IBA treatment, was with the
cuttings of the youngest tree (i.e., tree 13). Cuttings from young trees of
other species root better than those from older trees (Hyun 1967,
Hartmann and Kester 1983). In contrast, the lowest rooting success was
from the sprout cuttings of tree 3 followed by shoot cuttings of tree 11.
For unknown reasons, many cuttings from these two clones rotted without
rooting.
Fig. 3.
Vegetatively propagated red alder trees at the end of the first growing season.
29
Average rooting of terminal and nonterminal cuttings made from tree
12 were 100% and 64%, respectively. Working with European alder,
Martin and Guillot (1982) reported that terminal cuttings rooted better
than either middle or basal cuttings. Better rooting of "shoot tips" in
alder and other plant species may be due to higher concentrations of
endogenous root-promoting substances in the terminal bud (Hartmann
and Kester 1983). Terminal cuttings also have the added advantage of
having one less cut surface than nonterminal cuttings; this reduces the
possibility of invasion by disease organisms during and after rooting.
Cuttings of some trees rooted well without any IBA treatment. The
IBA treatments, however, appeared to be generally beneficial. On the
average, rooting was faster and greater with than without IBA (75.7% vs.
57.1%). Also, differences between the IBA treatments in their stimulating
effect on rooting of cuttings of the different trees were small and inconsis­
tent. For all clones, however, best results (80.0%) were obtained with a
10-sec dip in 2,000 or 4,000 ppm IBA. Previously, red alder cuttings
from young seedlings were successfully rooted after treatment with 4,000
and 8,000 ppm IBA (Monaco and others 1980). Preliminary experiments
in our laboratory indicated that 8,000 ppm IBA delayed and reduced
rooting compared with the less concentrated IBA treatments.
Growth and establishment of new plants from rooted cuttings
After potting, the rooted cuttings grew well in the greenhouse until they
were transferred to colder conditions to harden off. The dormant planting
stock resumed growth in the spring after it was outplanted. By the end of
the 1987 growing season, the new trees appeared healthy and ranged from
0.5 to 1.5 m tall. These trees (Fig. 3) will be heavily pruned next year, and
more cuttings will be taken from the shoots for propagation of more
plants from the same clones to establish new clonal plantations.
Acknowledgments
This work was supported in part by the U.S. Department of Energy,
Biomass Energy Technology Division, Short Rotation Woody Crops
Program. The first preliminary experiments with epicormic sprouts of red
alder were started by Dr. D. D. Hook, Clemson University, SC, while he
was on sabbatical leave at the Forestry Sciences Laboratory, Olympia,
WA.
30
Note
1 . The use o f trade names i n this publication i s for the information and convenience of
the reader and does not constitute an endorsement by the U.S. Department of
Agriculture of any product to the exclusion of another that may be suitable.
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