488
Clonal selection prospects in western hemlock combining rooting traits with juvenile
height growth
G. SAM FOSTER1
Department of Forest Science, Oregon State University, Corvallis, OR, U.S.A. 97331
ROBERT K. CAMPBELL
United States Department of Agriculture, Pacific Northwest Forest and Range ExperimetltStation, Forest Sciences Laboratory, Corvallis. OR. U.S.A. 97331 AND
W. THOMAS ADAMS
Department of Forest Science, Oregon State University, Corvallis, OR, U.S.A. 97331
Received July 18, 19842
Accepted December 20, 1984
FOSTER, G. S., R. K. CAMPBELL, and W. T. ADAMS. 1985. Clonal selection prospects in western hemlock combining rooting
traits with juvenile height growth. Can. J. For. Res. 15: 488-493.
Variation in 1st-year height (HT) of western hemlock (Tsuga heterophylla (Raf.) Sarg.) rooted cuttings was partitioned into
environmental and genetic components. C effects, a unique type of environmental effect, was highly significant and made up
8% of the total variation. Much of the variation (21%) resulted from genetic control of HT, producing a broad-sense heritability
of 0.81. As reported in a previous paper, initial rooting ability of the rooted cuttings affected the I st-year height growth of
the trees. Genetic correlations between HT and the five rooting traits ranged from 0.37 to 0.59. Using a selection index
(assuming 33% selection intensity) containing both HT and a rooting trait (VOL) would result in gains of 8-10% for HT and
20-34% for VOL, depending on relative economic weights for the two traits.
FOSTER, G. S., R. K. CAMPBELL et W. T. ADAMS. 1985. Clonal selection prospects in western hemlock combining rooting
traits with juvenile height growth. Can. J. For. Res. 15: 488-493.
La variation de Ia hauteur a un an (HT) de boutures racinees de pruche de !'ouest (Tsuga heterophylla (Raf.) Sarg.) a ete
subdivisee en composantes environnementale et genetique. Les effets C, type tres particulier d'effets environnementaux,
etaient tres significatifs et representaient huit pour cent de Ia variation totale. La plus grande partie de Ia variation (21%) de
Ia hauteur est sous contrOle genetique avec une heritabilite au sens large de 0,81. Tel que mentionne dans une etude anterieure,
!'aptitude precoce a l'enracinement influen<;ait en premiere annee Ia croissance en hauteur des arbres. Les correlations
genetiques entre HT et les cinq caracteristiques d'enracinement variaient de 0,37 a 0,59. L'utilisation d'un indice de selection
(en supposant une intensite de selection de 33%) incluant HT et une caracteristique d'enracinement (VOL) produirait un gain
de 8-10% pour HT et de 20-34% pour VOL, selon le poids economique relatif des deux caracteristiques.
[Traduit par le journal]
Introduction
Inheritance accounts for a substantial part of the variation in
rooting ability (Sorensen and Campbell 1980; Foster et al.
1984) and growth rate (Foster and Lester 1983) in western
hemlock (Tsuga heterophylla (Raf.) Sarg.). Genetic improve­
ment in both traits should therefore be possible. When selecting
for more than one trait, three somewhat different procedures
can be used: tandem selection, independent culling level, or
index selection (Hazel and Lush 1942). Based on theoretical
considerations (Hazel 1943) and practical demonstration
(Hazel and Lush 1942), index selection is considered to be the
most efficient of the three. This paper presents results of an
experiment in which a selection index is used to evaluate com­
bined selection for rooting characteristics and juvenile height in
western hemlock.
Wilcox and Farmer (1968) and Ying and Bagley (1974)
evaluated the association between rooting ability and shoot
growth for cottonwood (Populus deltoides Bartr.) clones and
Struve et al. (1984) investigated this association for eastern
white pine (Pinus strobus L.). White Wilcox and Farmer
(1968) found no significant association between these traits,
'Present address: Crown Zellerbach Corp., Forestry Services and
Research, Bogalusa, LA, U.S.A. 70427.
2Revised manuscript received December 13, 1984.
Ying and Bagley (1974) found that rooting ability and 1st-year
0.17). Struve
height growth were positively correlated (r
et al. (1984) detected significant correlations between numbers
of roots per rooted cutting (at planting) with diameter at breast
height at 7 years ( r
0.43) and 40 years (r
0.42) of age.
In the same study, there was no significant correlation between
number of roots and height at 40 years.
Even though the potential benefits of using selection indices
in forest tree improvement are large (Stonecypher 1970), forest
geneticists have been slow to use indices because of several
problems with their application (Arbez et al. 1974). These
problems include the following: (i) economic weights are bene­
ficial for selection indices, yet they are difficult to determine
in forestry because of changing market conditions; (ii) index
construction depends upon accurate estimates of genetic and
phenotypic variances and covariances, which can be obtained
only from large and precise studies. Despite these problems,
forest geneticists have begun to employ index selection while
attempting to resolve problems. Bridgwater (1972) used index
selection for multiple-trait selection of cottonwood clones.
Height, diameter, specific gravity, volume, and dry weight
were included in Bridgwater's index as traits for improvement.
He dealt with the problem of inadequate economic information
by conducting a sensitivity analysis of economic weights.
The objectives of this current study were (i) to provide infor­
=
FOSTER ET
TABLE
AL
489
I. Environmental conditions in a growth experiment using hemlock rooted cuttings
Relative
Duration of light intensity" (h:min)
Temperature
humidity
Date�>
(OC)
(%)
0"
1 / l l /1982-2/11/1982
5
60-70
16:00
2/12/1982
7
50
15:20
2
3
2
1:45
2:00
0:30
2:00
1:45
1:55
2:10
0:30
2:10
1:55
0
2/13/1982
9
50
14:40
2:05
2:20
0:30
2:20
2:0
2/14/1982
II
55
14:00
2:15
2:30
0:30
2:30
2:15
2/15/1982
13
60
13:30
2:30
2:30
0:30
2:30
2:30
2/16/1982
15
65
13:00
2:30
2:45
0:30
2:45
2:30
2/17/1982
17
65
12:30
2:45
2:45
0:30
2:45
2:45
2/18/1982
19
65
12:00
2:45
3:00
0:30
3:00
2:45
2/19/1982-4/11/1982
21
65
5:45
2:45
3:00
0:30
3:00
2;45
5:45
0:30
4/12/1982-5/28/1982
21
65
5:45
2:45
3:00
1:00
2:30
2:45
5:45
0:30
"From 2/19/1982 to 5/28/1982, the 11.5-h night was broken in half by 0.5 h of light.
"Month/day/year.
"Light intensities: 0, dark;
I, 150 flE m-2 s-1; 2, 290 j.lE m-2 s-•: 3, 430 flE m-2 s-•.
mation to the network analysis (Foster 1983) of research and
development for clonal reforestation with hemlock, (ii) to de­
termine genetic and phenotypic associations between rooting
traits and 1st-year height growth of hemlock clones, (iii) to
compare genetic gains for selection of juvenile height (with the
accompanying indirect response for rooting traits) with com­
bined selection for height and rooting traits utilizing index
selection, and (iv) to recommend a selection procedure for
juvenile growth and rooting ability.
Materials and methods
The clones used in this study were a subset of clones used in a
rooting experiment, for which the rooting procedures have previously
been reported (Foster
et
al. 1984). Of the 60 clones in the rooting
experiment, 30 were chosen that produced enough rooted cuttings to
meet design requirements of this study.
The following five rooting traits were scored for each of the 30
clones: number of rooted cuttings per five-cutting plot (RC), length of
the longest main root on each rooted cutting (L TH), number of main
TABLE
2. Form of the analysis of variance for total height (HT) of
hemlock clones grown in a controlled environment
Source of variation
df
Expected mean squares"
l
Growth chambers (H)
8
Blocks (B)/H
29
Clones (C)
Primary ramets (P)/C
60
HxC
29
60
HXP/C
Error
"h.
712
cr2+ bcr P(C)+bpcr c+cpcr (H)+bcpe
cr2+cpcr (Hl
cr 2+hbcr2P(C) +hbcr
cr2+hbcr!,Cl
cr2+bcr P(Cl+bpcr c
cr2+bcr P<Cl
cr 2
°
b, c, and pare adjusted values of the number of growth chambers, blocks, clones,
and primary ramets, respectively:
0 , effects owing to growth chamber differences; cr <H>.
variance among blocks within growth chambers; cr , variance among clones; cr C>·
variance among primary ramets within clones; cr c• variance owing to interaction of
cr P(C)• variance owing to interactions of
growth chambers and clones;
and primary ramets within clones.
growth chambers
roots (roots beginning at the cutting base) per rooted cutting (MR),
sum of the lengths of all main roots per rooted cutting (VOL), and
discharge Lucalox high-pressure sodium lamp bulb. These bulbs were
number of quadrants (of the cutting base) from which main roots arise
set at three intensities (150, 290, and 430 fJ.E m-2 s-1) referred to as
per rooted cutting (QD). Because only cuttings with roots could be
used in this study, there were no zero values for any of the traits.
After scoring the traits, the 30 clones were potted into 352.6-mL
cells. The potting medium consisted of equal parts of sand, shredded
light intensities l , 2 and 3, respectively. Using these settings, the light
intensity was varied during the day to simulate the natural lighting
pattern with an intensity that increased during the morning, peaked at
noon, and then decreased (Table 1).
peat moss, and perlite. The medium was steam sterilized before use.
The trees were watered once a week with deionized water or with
The potted, rooted cuttings were then placed in a greenhouse and
a nutrient soil drench, on alternating weeks from February 25, 1982,
maintained at temperatures between 10 and 20°C (using heating as
until the end of the study. The drench was made up as a I : l : l ratio
needed) for the next 6 months. The cuttings received a normal (avoid­
of nitrogen, phosphorus, and potassium applied at 150 ppm in di­
ing unnatural water stress) watering regime and natural daylight
onized water plus 30.1 g of Sequestrene iron and 0.75 g of Peter's
during this period. A balanced fertilizer was added during normal
Special S.T.E.M. (soluble trace elements mix) micronutrients in
108.5 L of deionized water.
watering cycles.
In January 1982 (6 months after scoring rooting traits), the rooted
The experimental design consisted of five blocks in each of two
cuttings were moved from the greenhouse into two growth chambers
growth chambers. Each block contained 30 clones. In a block, each
(model M-1148, Environmental Growth Chamber Co.) and subjected
clone was represented by six secondary ramets. The secondary ramets
to a growing regime which had previously been used successfully to
were two each from three primary ramets. A primary ramet is a cutting
grow hemlock seedlings in the chambers. During the first 4 weeks in
taken directly from the ortet (a 30- to 50-year-old hemlock in western
the chambers, short day lengths (8 h) were used along with constant
Oregon), rooted, and grown in a greenhouse to supply secondary
temperature (SOC) and relative humidity (60-70%) (Table l ) to pro­
cuttings. When rooted, these secondary cuttings become secondary
vide chilling. Then, after an 8-day transition period of increasingly
ramets.
warmer temperatures and increasing day length, growing conditions
Total height (HT) of each rooted cutting was measured to the
were held essentially constant for the 3-month growing period
nearest 0.5 em. The typically drooping terminals of hemlock were
(Table 1).
Lighting was provided by a combination of G.E. (General Electric
straightened for measurement. Survival of rooted cuttings at the end
of the growing period was 99.5%.
Co.) high-intensity discharge lamps. Each of the three fixtures per
Two analyses of variance were used, the first to partition HT into
a G.E. high-intensity dis­
several environmental and genetic components and the second to
a G.E. high-intensity
estimate components of variance and covariance for calculating ge­
chamber contained two types of bulbs:
(i)
charge "R Multi-Vapor Lamp," 400 W, and
(ii)
490
CAN. J. FOR. RES. VOL
TABLE 3. Fonn of the analysis of variance (and covariance) used for
estimating components of variance (and covariance) for total height
(HT) and rooting traits (RC, LTH, VOL, MR, and QD) of hemlock
TABLE 5. Analysis of variance for total height (HT) of hemlock
clones using the complete model
Source of
clones
mean squares"
df
Clones (C)
2
a +na tc)+npa
2
2
cr + fl(J' P<Cl
29
Primary ramets (P)/C
60
Error
(]'2
810
"n is the number of plots per primary r•met and p is the number of primary ramets per
clone;
variance among clones;
cr c,. variance among primary ramets within clones;
0'2• error variance.
TABLE 4. Mean
values for five
rooting traits and total height in two samples
of hemlock clones
Trait"
HT (em)
RC (no.)
MR (no.)
QD (no.)
LTH (em)
VOL (em)
Rooting
experimentb
Growth
experiment"
2.67±0.04
2.50±0.04
20.3±0.15
3.92±0.03**
3.13±0.05**
1.90±0.02
4.65±0.07
8.12±0.17
2.23±0.03**
5.79±0.08** 11.33±0.22** "Traits are as defined in the text. "Means from a 60-clone rooting experiment (Foster el al. 1984).
"Means from a 30-clone subsample of clones from the
rooting experiment; **, significant at
Mean
squares
variation
Expected
Source of variation
15, 1985
I% level.
Variance
component"
the missing values. Coefficients of variance and covariance compo­
nents were adjusted for the unbalanced design (Searle 1971).
In the second analysis (Table 3), a nested design is assumed with
30 clones, three primary ramets per clone, and 10 plots per primary
ramet. Plots consisted of the two secondary ramets per primary ramet
in each block. This analysis is different from the first because of some
requirements for estimating genetic correlations. For genetic cor­
relations, the covariance among clone means for height and rooting
traits should be free of error covariance. But the rooting experiment
provided the data for rooting traits and also the ramets for the growth
experiment. Errors in the two experiments might therefore be cor­
related. Some further complications were that the rooting experiment
and growth experiment had different numbers of blocks and that
blocks in the rooting experiment furnished unequal numbers of ramets
for the growth experiment. The problem was partly ameliorated by
pooling cuttings from the blocks of the rooting experiment and re­
randomizing them into plots for the growth experiment. Then for the
analysis, rooting data for each secondary ramet were adjusted (adding
or subtracting block mean deviations from the grand mean) for differ­
ences among the blocks in the rooting experiment and growth data for
ramets were adjusted for the differences between growth chambers.
The analysis was based on plot means, being the average of adjusted
data for the two secondary ramets per primary ramet per bloek.
Variance and covariance components for the five rooting traits (RC,
LTH, VOL, MR, and QD) and total height (HT) were derived from
the second analysis by equating mean squares (or mean cross products)
to expected mean squares (or mean cross products) and solving equa­
2
tions (Table 3). Broad-sense heritabilties (H ) on a clone-mean basis
were calculated for all traits as follows (symbols defined in Table 3):
Percent
of total
Growth
chambers (H)
e
400.35**'
Blocks (B)/H
18.91NS
Primary ramets
Hxc
0.06±0.10
CTc
4.45±1.40
a;(cJ
2
(J'HC
2
9.09NS
HXP/C
l 5.48NS
Erro
13.31
(J'HP(Cl
(]'
2
28.8,
and p = 3 (refer to Table
2
21
I .75±0.57
8
0.00±0.25
0
0.45±0.60
2
13.31±0.72
64
"Adjusted values of the coefficients of variance components were
c =
4
CTso-1;
?
30. 15**
(P)/C
0.89
2
2
158.41**
Clones (C)
h
4.8,
for explanation of symbols).
•Mean ±SE (Namkoong 1979).
'A synthetic F test, after the technique of Cochran
ferences among growth chambers.
5%
•, Significant at
(1951), was used to test for dif­
I% level; NS, not significant at the
level.
TABLE 6. Parameter estimates for total height (HT) in
a population of hemlock clones
Parameter
Value
Mean (i)
Range of plot means Phenotypic standard deviation (frx) Coefficient of variation (frx/i) Heritability
(H2) "Mean ± SE (Namkoong
netic correlations among HT and rooting traits. In the first analysis of
variance (Table 2), all effects except that of growth chambers were
considered to be random. The analysis was based on plot means.
Because of a shortage of rooted cuttings for some clones, a few plots
were missing. A least-squares analysis was employed to accommodate
/Estimate�>
(T
+
(T2
P(C)
P
20.13 em
7.25-34.75 em
2.35 em
12%
0.81±0.06"
1979).
A
2
+ Q_
np
Genetic and phenotypic correlations among the six traits were also
estimated using the technique of Johnson et al. (1955).
To assess potential gains that may be made by combining selection
for HT with selection for rooting traits, selection indices were calcu­
lated. Indices, direct gains, and indirect gains were calculated using
techniques described by Van Vleck (1981).
Selection indices normally require estimates of the net economic
value of each trait. Unfortunately, the economic value of rooting traits
and 1st-year height of hemlock have not been assessed. Ideally, the
impact of root-shoot ratios on subsequent tree growth could be used
to assign economic values to height and to rooting traits, but this
information is not yet available for hemlock. A sensitivity technique
(Bridgwater 1972) was therefore used for assigning economic weights
to the traits. Since increased yield is a major objective of most tree
improvement programs and juvenile height is an early indication of
yield, the relative economic weight of 1.0 was assigned to HT and
weights of 1.0, 0.5, and 0.0 were assigned in separate calculations to
one rooting trait. The results of these indices were then compared with
direct selection for HT only. Using an economic weight of 0.0 for the
rooting trait produces a different index than selecting only for HT. An
index including the rooting trait, even with an economic weight of O.O,
takes advantage of the genetic covariance between HT and the rooting
trait to select for HT; deleting the rooting trait entirely from the index
does not make use of its covariance to improve selection.
Results
Because 20 cuttings per ramet were needed in the growth
experiment, clones which rooted poorly in the rooting experi­
491
FOSTER ET AL.
TABLE 7. Analysis of variance for six traits of hemlock clones using the second model
Mean squares"
Source of
variation
Clones (C)
Primary ramets (P)/C
Errore
HT"
RC
MR
QD
LTH
VOL
158.36**
30.10**
13.37
6.12**
2.09*
0.38
24.25**
3.11*
1.35
5.72**
0.78**
0.47
51.23**
6.88* 3.59
530.00** 72.54**
2o.n" "Adjusted values of the coefficients of variance components were 11 = 9.6 and p
explanation of the symbols). *, Significant at the
5%
level:
I%
significant at the
=
3 (refer to Table
3
for an
leveL
"Traits are defined in the text.
0As a result of missing plots, df
=
810.
TABLE 8. Phenotypic (above diagonal) and genetic (below diagonal) correlations (±SE)
among five rooting traits and height of hemlock cuttings
Trait"
Trait
RC
MR
LTH
VOL
QD
HT
MR
LTH
VOL
QD
HT
0.71±0.09
0.51±0.13
0.47±0.14
0.73±0.09
0.85±0.05
0.83±0.05
0.71±0.09
0.95±0.02
0.49±0.14
0.81±0.06
0.35±0.16
0.46±0.14
0.50±0.14
0.52±0.13
0.53±0.13
RC
0.91±0.12
0.63±0.17
0.95±0.11
0.87±0.11
0.37±0.22
0.48±0.16
0.87±0.06
0.98±0.02
0.49±0.17
0.84±0.06
0.53±0.16
0.50±0.16
NOTE: All correlations arc significant at the
0.87±0.07
0.53±0.16
0.59±0.15
1% level.
"Traits are defined in the text.
TABLE 9. Genetic gains" in measurement units and percent of means (in parentheses) for hemlock clones
from different selection strategies emphasizing HT and VOU'
Relative
economic
weights
Gain
HT
VOL
LTH
QD
HT
VOL
Index
(em)
(em)
(em)
(no.)
MR
(no.)
(no.)
1.0
1.0
1.0
1.0
1.0
0.5
0.0
0.84HT+0.88VOL
0.8IHT+0.46VOL
0.78HT+0.037VOL
0.8IHT
1.67(8)
1.85(9)
2.09(10)
2.08(10)
3.84(34)
3.59(32)
2.3 I (20)
2.06(18)
1.04(18)
0.98(17)
0.62(1I)
0.61(11)
0.36(16)
0.35(16)
0.32(14)
0.24(11)
0.72(23)
0.68(22)
0.45(14)
0.41(13)
0.33(8)
0.30(8)
0.17(4)
0.13(3)
"Assume a selection intensity of
10
out of
30
clones or i
=
RC
l.097.
"Traits are defined in the text.
ment seldom were used in the growth study. Truncation of the
original population from 60 to 30 clones consequently selected
clones with better rooting ability, producing higher mean
values for rooting traits in the growth experiment than in the
rooting experiment (Table 4).
Differences in total height of cuttings between growth cham­
bers, among clones, and among primary ramets within clones
were all statistically significant (Table 5). The plot-mean
height of cuttings was 20.13 em with a range of 7.25 to
34.75 em; the coefficient of variation was 12% (Table 6).
Cuttings from one growth chamber were 1.35 em taller than
those from the other, although the two chambers were set for
the same conditions. Clonal variance (genetic variance) ac­
counted for 21% of the total variation in the experiment and
variance owing to differences among primary ramets within
clones (C effects variance) accounted for 8%; therefore, vari­
ation in height owing to C effects was approximately one-third
the size of total genetic variation (Table 5).
A second analysis (Table 7) provided estimates of the com­
ponents of variance and covariance. Components were then
used to estimate genetic parameters. The broad-sense herit­
ability of HT was 0.81 (Table 6); with C effects included, H2
was 0.92. The heritabilities estimated for rooting traits were
similar to but consistently lower than those obtained from the
60 clones used in the rooting experiment (Foster et al. 1984)
(i.e., RC (0.66 vs. 0.87), MR (0.87 vs. 0.92), QD (0. 86 vs.
0.89), LTH (0.87 vs. 0. 87), and VOL (0.86 vs. 0.90)).
Juvenile height was genetically associated with desirable
attributes of rooting as evidenced by genetic correlations that
were positive and moderately large (Table 8). The genetic
correlations of HT with the five rooting traits ranged from 0.37
to 0.59 and phenotypic correlations ranged from 0.35 to 0.53.
The rooting traits were themselves highly and positively cor­
related both genetically and phenotypically.
Only one of the rooting traits, VOL, was chosen for use in
a selection index with HT. Except for QD, VOL had the largest
genetic correlation with HT and the measurement of VOL is
much less subjective than for QD. VOL and QD were both
highly correlated with other rooting traits.
Selection for rooting traits theoretically can be used to im­
prove selection for juvenile height (Van Vleck 1981) because
of the strong positive correlations among HT and rooting traits.
CAN. J. FOR. RES. VOL. 15, 1985
492
In fact, when VOL with zero economic weight was included in
the selection index, gain in height was essentially the same as
with selection for height alone (Table 9). When the relative
economic weight for VOL was increased from 0.0 to 0.5, there
was a minor decrease in gains for HT (10 to 9%) and a substan­
tial increase in gains for VOL (20 to 32%). In addition to larger
gains in VOL, gains in LTH, QD, MR, and RC, owing to
indirect selection (via their correlation), also increased substan­
tially. Little additional gain in VOL, or in other rooting traits,
resulted from further increases in the economic weight of VOL.
Discussion
The large heritabilities, the significant vanatmn among
clones, and the strong correlations among height and rooting
traits suggest that significant genetic gains in both height and
rooting success will be possible. The positive correlations we
found between growth and rooting are, however, in contrast
with results of Wilcox and Farmer (1968), but this may be a
matter of time and conditions of measurement. Ying and
Bagley (1974) reported that the correlation between number of
roots per cutting and height growth of rooted cuttings decreased
with increasing age of the plantation (i.e., from 0.17 at 1 year
to -0.04 at 7 years of age). Ying and Bagley's (1974) results
suggest that early height growth is related to rooting ability
(especially for clones which root poorly) through a limiting
process; size of the root system may limit shoot growth through
physiological processes. After the root system has had time to
develop fully in the field, the limiting association declines and
finally disappears. This means that experiments to relate
rooting ability with growth at later ages are needed before
deciding on a system for selecting clones for commercial use.
Nevertheless, our strong and positive correlations indicate that
hemlock clones that root poorly will probably grow slowly in
the year or two after outplanting. Such clones also may not
survive well in the harsher environments of commercial planta­
tions.
The results of this study and of a previous rooting experiment
(Foster et al. 1984) suggest several ways to select hemlock
clones more efficiently. One way is to partition the sources of
environmental variation at every step in the cloning procedure.
Clonal performance was strongly affected by environment,
from cutting to cutting within the ortet or hedged (primary)
ramet, from block to block in the rooting bed, and from growth
chamber to growth chamber in the growth phase. After these
effects were accounted for in our experiment, clonal means
were estimated very precisely.
Secondary cloning should therefore be a part of the rooting
procedure, especially in early phases of selecting clones. In this
experiment, variation in C effects in HT arose despite efforts to
minimize the variation by hedging and by growing the hedged,
primary ramets in uniform conditions. This nongenetic vari­
ation could have originated directly in the original size of the
cuttings (i.e., the observed correlation between cutting length
and HT was 0.13), or the variation could have originated indi­
rectly through other C effects passed on from the rooting
experiment. Clones also varied in age and vigor of the ortet.
C effects for rooting traits were large even after hedging and
would have been larger without it (Foster et al. 1984).
At every stage of the rooting procedure a randomized block
or other suitable design can be used to minimize bias in
selecting clones. Based on results from the rooting experiment,
some equally efficient designs in the rooting bed are (i) three
primary ramets per clone and four or six blocks and (ii) five
primary ramets per clone and two blocks.
Blocking should be used also if cuttings are to be potted or
transplanted before selection for early growth. An efficient
design cannot be recommended from our ��suits because vari­
ation among growth chambers cannot be equated realistically to
variation among blocks of pots or in a transplant bed.
Selection of clones probably can, be made more efficient by
selecting for rooting traits as well,as for growth traits. Although
we were unable to arrive at concrete costs and benefits,
improved rooting ability has several economic advantages: (i)
fewer primary ramets will be needed to provide the necessary
number of cuttings, thus saving maintenance and development
costs for the primary ramets; (ii) smaller rooting facilities, and
therefore Jess labor and supplies, will be needed to supply the
desired number of rooted cuttings; (iii) costs associated with
aftercare, following lifting of cuttings from the rooting bench,
may be less if the rooted cuttings are ready for field planting in
a shorter period of time; and (iv) if survival of field-planted
cuttings is higher, then fewer rooted cuttings will be needed to
achieve a desired stocking level and associated planting costs
will be reduced. Consequently, improving rooting ability in a
population of hemlock clones may have substantial economic
benefits throughout the entire process of propagation and stand
establishment.
If the relative values of rooting traits and growth trmts are
known, selection by index will maximize genetic improvement
in its combined trait. In the absence of such values, our results
indicate that economic weights in the ratio 1.0:0.5 for HT and
VOL will bring about substantial improvement in all rooting
traits. At the same time, the percentage improvement in HT
will be only slightly decreased.
We believe that clonal selection of hemlock can be made
significantly more efficient by following the suggestions
above. In all of the previous steps, careful records should be
kept on costs associated with hedging, secondary cloning,
blocking, and rooting. Also, data on subsequent growth of
cuttings should be gathered from field tests carried to one-third
or one-half rotation age. This information is needed to develop
appropriate economic weights, along with quantitative data to
support the benefits of improving juvenile height growth and
rooting ability. Because the correlation between rooting ability
and height growth of juvenile trees with height or volume
growth of older trees is still unknown for hemlock, predicted
gains in this paper apply only to 1st-year height.
Acknowledgements
This paper represents a portion of the senior author's Ph.D.
dissertation. The authors would like to thank Crown Zellerbach
Corporation for providing the plant material, facilities, and
financial support for this project.
ARBEZ, M., P. BARADAT, J. P. MAUGE, C. MILLER, and J. BODIA.
1974. Some problems related to use of selection indices in forest
tree breeding. Proceedings of the Joint IUFRO Meeting, Session II,
Stockholm, Sweden, September, 1974. Royal College of Forestry,
Department of Forest Genetics, Stockholm, Sweden. pp. 97-116.
BRIDGWATER, F. E., JR. 1972. Multiple trait selection in a population
of eastern cottonwood. Ph.D. dissertation, Oklahoma State Univer­
sity, Stillwater, OK.
COCHRAN, W. G. 1951. Testing a linear relation among variances.
Biometrics, 7: 17-32.
FosTER, G. S. 1983. Genetic considerations in cloning western hem­
lock. Ph.D. dissertation, Oregon State University, Corvallis, OR.
FOSTER, G. S., and D. T. LESTER. 1983. Fifth-year height variation
FOSTER ET AL.
in western hemlock open-pollinated families growing on four test
sites. Can. J. For. Res. 13: 251-256.
FOSTER, G. S., R. K. CAMPBELL, and W. T. ADAMS. 1984. Heri­
tability, gain, and C effects in rooting of western hemlock cuttings.
Can. J. For. Res. 14: 628-638.
HAZEL, L. N. 1943. The genetic basis for constructing selection in­
dexes. Genetics, 28: 476-490.
493
SORENSEN, F. C., and R. K. CAMPBELL. 1980. Genetic variation in
rootability of cuttings from one-year-old western hemlock seed­
lings. USDA For. Ser. Res. Note PNW-352.
STONECYPHER,
R.
W.
1970.
Multiple-trait
(N.Y.), 24(2-3): 48-51.
breeding.
/
Unasylva
STRUVE, D. K., 1. T. TALBERT, and S. E. McKEAND. 1984. Growth
of rooted cuttings and seedlings in a 40-year-old plantation of
eastern white pine. Can. J. For. Res. l4: 462-464.
HAZEL, L. N., and J. L. LUSH. 1942. The efficiency of three methods
of selection. 1. Hered. 33: 393-399.
VAN VLECK, D. 1981. Notes on the theory and application of selec­
JOHNSON, H. W., H. F. ROBINSON, and R. E. COMSTOCK. 1955.
tion principles for the genetic improvement of animals. Cornell
Genotypic and phenotypic correlations in soybeans and their
implications in selection. Agron. J. 47: 477-483.
NAMKOONG, G. 1979. Introduction to quantitative genetics in fores­
try. U.S. Dep. Agric. For. Serv. Tech. Bull. No. 1588.
SEARLE, S. R. 1971. Linear models. John Wiley & Sons, Inc., New
York.
.
University, Ithaca, NY.
WILCOX, J. R., and R.
E. FARMER, JR. 1968. Heritability and
C effects in early root growth of eastern cottonwood cuttings.
Heredity, 23: 239-245.
YING, C. C., and W. T. BAGLEY. 1974. Genetic variation of eastern
cottonwood. Univ. Nebr., Dep. For., Prog. Rep. No. I.