Transcript Non-additive variance in P. abies and its influence on

Non-additive variance in P. abies
and its influence on tree breeding.
By: Johan Weston
 What is the level of additive
& non-additive variance for
early height growth in our
clonal tests?
 Are clonal tests suitable for
a breeding strategy based
on general combining
ability?
 Can we affect the level of
non-additive variance?
Forestry Research Institute
Sävar
Overview of Material & methods
 Half-sib & full sib clones
 Selection of ortets based on early height




growth in the nursery
Clonal field-tests – 2 series, 10 tests
Complete randomisation, single tree plots
Assessment of height growth (10-11 yrs)
Estimation of variance components - ASReml
Conclusions
 Overall, non-additive variance was substantial
but smaller than additive variance
 Non-additive variance was affected by
clonal origin and test environment (”frost”)
 Clonal tests are suitable in a breeding strategy
based on general combining ability (GCA)
- if non-additive variance is moderate
 To increase trait heritability and selection
accuracy a more distinct definition of the trait
”growth” is needed
Half-sib material
ºN
68
 2 clones selected in
each family 66
 clones divided in
64
southern and northern
origins
62
 6 clonal field tests
60
 assessment after 11
years
58
56
Selected plustrees
in natural stands
and field tests
Sävar
Full-sib material
ºN
68
 partial diallel
Selected plustrees
in natural stands
66
 3-7 ortets selected in
each family 64
 4 clonal field tests
62
 assessment after 10
60
years
58
56
Sävar
Test material
Hedge archive at Sävar
Rooting of cuttings in nursery
Field-tests
A newly established field-test (1991)
 complete
randomisation
 single-tree plots
 ca.2 cuttings / clone
 post-blocking
Statistics
 ASReml [25 Jan 2001]
 Model - half-sib clones
Y= µ +
Testsite + Block +
Stand + Parent + Clone
(Fixed)
(Random)
 Model - full-sib clones
Y= µ +
Testsite + Block +
Parent + Fam + Clone
(Fixed)
(Random)
Estimation of additive and nonadditive variation – half sib clones
 Parent (mother) component of variance, σp2
 Clonal component of variance, σc2
 σA2 = 4σp2
 σNA2 = σc2 - 3σp2
 Stand component of variance, not included in
σA2 , a ”provenance” effect
(Source: Snedden et al, 2000, In "Forest Genetics for the Next
Millenium ”, IUFRO 2.08.01)
Results half-sib clones
Overall
Southern
Northern
2 mid-tests
824
1603
441
854
383
749
824
1590
2
12
2
11
2
13
2
6
196,9
207,7
185,9
192,9
CVA
0,09
0,07
0,12
0,12
h2
H2
0,07
0,18
0,04
0,17
0,11
0,19
0,11
0,23
74
207
-1
24
Families
Clones
Clones/family
Cuttings/fam
Height, cm
VNA/VA%
VNA/VA as families are excluded (from south)
800
600
VNA / VA , %
Half-sib clones southern origins
400
200
0
VA and VNA variance levels as families are
excluded (from south)
-200
55
1000
56
57
59
60
61
Minimum latitude, °N
800
600
400
Average height and latitudinal origin
200
300
0
250
-200
55
56
57
58
59
Minimum latitude, °N
60
61
VA
62
VNA
Tree height, cm
Variance
58
200
150
100
50
0
56
57
58
59
60
61
62
Latitude °N, (class bottom)
63
64
62
Estimation of non-additive
variance – full-sibs
 Parent component of variance, GCA, σp2
 Family component of variance, SCA, σf2
 Clonal component of variance, σc2
 Additive variance, σA2 = 4σp2
 Total genetic variance, σG2 = 2σp2 + σf2 + σc2
 VNA= Total genetic variance – additive var.
= σG2 - σA2
(Source: Mullin et al, Can J For Res, 1992 )
Results full-sib clones
Overall
"No frost"
"Frost"
141
642
140
635
141
631
5
31
5
16
4
15
133,4
147,9
118,5
h2
H2
0,06
0,10
0,09
0,11
0,06
0,11
CVA
0,10
0,12
0,09
51
17
95
Families
Clones
Clones/family
Cuttings/family
Height, cm
VNA/VA%
VNA/VA in the field-tests
Full-sib clones
1000
VNA/VA, %
800
Variance levels in the field-tests
600
400
200
1000
0
"No frost"
600
400
"Frost"
Average height in the field-test
VA
300
VNA
250
200
0
"No frost"
"Frost"
Tree height, cm
Variance
800
200
150
100
50
0
"No frost"
"Frost"
Hypothesis
 NAV in height growth is influenced y genetic
variation in other traits i.e. hardiness
 Buds are more frost sensitive in genetic
material with a long growth period
 Genetic entries with a long growth period has a
high growth potential
 Occasional bud damages due to frost may be
included in the trait ”height growth”
Conclusions
 Overall, non-additive variance was substantial
but smaller than additive variance
 Non-additive variance was affected by
clonal origin and test environment (”frost”)
 Clonal tests are suitable in a breeding strategy
based on general combining ability (GCA)
- if non-additive variance is moderate
 To increase trait heritability and selection
accuracy a more distinct definition of the trait
”growth” is needed
Estimation of VNA with half-sib clones

Family component of the variance,
σp2 = ¼ σA2

Clonal component of the variance = total genetic variance minus the family
component,
σc2 = σG2 - σp2
 σc2 = (σA2 + σNA2) - σp2
σc2 = (σA2 + σNA2) - ¼ σA2
σc2 = ¾ σA2 + kσNA)
σc2 = ¾ σA2 + σNA
k = proportion of non-additive variance segregating within families, k=1 in
o.p. families (Park & Fowler, 1987)
 σNA = σc2 - ¾ σA2
σNA = σc2 - ¾ (4σp2 )
σNA = σc2 – 3σp2
(Source: Snedden et al, 2000, In "Forest Genetics for the Next Millennium”,
IUFRO 2.08.01)
Estimation of dominance and
epistasis
 Parent component of variance, GCA, σp2
 Family component of variance, SCA, σf2
 Clonal component of variance, σc2




Dominance variance, σD2 = 4σf2
Epistatic variance, σI2 = σc2 - 2σp2 - 3σf2
Total genetic variance, σG2 = 2σp2 + σf2 + σc2
NVA= Total genetic variance – additive var.
(Source: Mullin et al, Can J For Res, 1992 )
Litterature

Snedden, C.L., Verryn, S.D. & Roux, C.Z. 2000, Broad- and narrow sense heritabilites in a
cloned open pollinated Eucalyptus grandis breeding population, Proceedings In "Forest
Genetics for the Next Millenium ”, IUFRO Working Party 2.08.01, Durban, South Africa, p
214-220.

Mboyi, W.M. & Lee S.J., 1999, Incidence of autumn frost damage and lamma growth in a
4-year-old clonal trial of Sitka spruce (Picea sitchensis) in Britain. Forestry vol 72, No 2 ,
1999

Mullin, T.J., Morgenstern, E.K., Park, Y.S & Fowler, D.P., 1992, Genetic parameters from a
clonally replicated test of black spruce (Picea mariana), Can. J. For. Res. 22 : 24-36.

Mullin, T.J. & Park, Y.S. 1992, Genetic parameters and age-age correlations in a clonally
replicated test of black spruce after 10 years, Can. J. For. Res. 24 : 2330-2341.

Samuel, C.J.A., 1991, The Estimation of Genetic Parameters for Growth and Stem-Form
over 15 years in a Diallel Cross of Sitka Spruce, Silvae Genetica 40, 2.

Park, Y.S & Fowler, D.P., 1987, Genetic variances among clonally propagated populations
of tamarack and the implications for clonal forestry, Can. J. For. Res. 17: 1175-1180