Download Document

Variation in fertility and its impact on
gene diversity in a seedling seed
orchard of Eucalyptus tereticornis
Mohan Varghese 1, 2, N. Ravi 2, Seog-Gu Son 1, 3
and Dag Lindgren 1
•1 Swedish University of Agricultural Sciences, Umea, Sweden
•2. Institute of Forest Genetics and Tree Breeding, Coimbatore, India
•3. Korea Forest Research Institute, Cheongryangri, Seoul, Korea
Introduction
Progeny trials
• Serve as breeding
populations in short rotation
eucalypts
• Enables testing of fullsib and
half sib families – heritability
and breeding values
• Thinning and conversion to SSOs
Domestication of E. tereticornis
• Indian land race – Mysore gum
has narrow base, inbred and
suffers hybrid breakdown
• Breeding populations of natural
provenances and local
selections
• Poor flowering of natural
provenances in South India.
Study Material
• First generation open pollinated
progeny trial – 42 families of 17
provenances, 24 trees per family, 4
tree plots, incomplete block
design.
• Perfect flowers in umbels of 57/cluster.
• Outcrossed with protandrous
flowers, pollination could occur
between flowers of a tree or
between related trees.
Assessment
• Breeding values estimated from
combined index values.
• Number of primary, secondary
and tertiary branches and
number of flowers and fruits
recorded for each tree
• Flowers per tertiary branch and
stamens per flower recorded in
10 flowers per tree
• Fruits per secondary branch
recorded
Fertility estimation
• Male and female fertility assumed to be equal
to number of male and female gametes
produced by a tree
• Gender fertility assumed to be equal to
proportion of reproductive structures of a
tree
• Total fertility of a tree – average of male and
female fertilities.
Conversion to SSO
• Trees listed according to phenotypic value
for tree height.
• Hypothetical truncation of 20% best trees
(200 trees) to be retained after thinning
based on deviation of individual tree value
from overall mean
Sibling coefficient (A)
• Indicates the extent of variation in fertility
• Calculated from number of trees in the
orchard (N) and fertility of each tree (pi)
• A =N Σ pi 2
• Am =N Σ mi 2
• Af =N Σ fi 2
Group coancestry (Θ)
• The probability that two genes chosen at
random are identical by descent.
• Θ = 0.5Σ pi 2 - if the trees are non related
and non inbred
• Θ =Σ Σ pi pjθij - pi pj – probability that genes
originate from genotypes i and j; θij the
coancestry between i and j
Different sexes of parents
• Θ =Σ(mi+fj) Σ (mj+fj) θij
probability of maternal and
paternal fertility and an
interaction component
are considered.
Status Number (Ns)
• The number of unrelated and non inbred genotypes
in an ideal panmictic orchard – same coefft. of
inbreeding in crop as orchard parents.
• Ns = 0.5/ Θ
• Ns = 1/Σ pi 2 – if the trees are unrelated – the
effective population size
• The effective number of trees that contribute to
random mating.
Variance effective population
(v)
size (Ne )
• The size of the population that would give
same drift in gene frequencies in seed crop
as orchard parents.
• Ne(v) = A / [2 Θ(A-1)]
SSOM(Seeding Seed Orchard
Manager)
Input constant
Realtedness within familiy
Expectations of seed orchard
0.125
RUN
Number of trees
Group coancestry;
Q=S(mi+fi)S(mj+fj)qij=Spipjqij
Status number;Ns = 0.5 / Q
Sibling coefficient;
A = C.V.2+1
Variance effective population size;
Ne(v)=A/2Q(A-1)
Proportion
Input measurements
B.V.
fi
mi
pi
Input I.D
Family
Predicting relatedness across
generations
• Θ gamete is a function of inbreeding (F),
fertility variation (A) and number (N) of
parent trees
• Θ offspring= 0.5/Noffspring+(1-0.5/ Noffspring )Θ gamete
• Θ gamete =[ 0.5(1+F)A/N ] + (1-A/N)[ NΘ-0.5(1+F) ] / N-1
• Foffspring = Θ gamete
Gene diversity (GD) and
Heterozygosity (He)
• Reference population – natural forest is
considered to have infinite number of
unrelated individuals.
• GD = 1- Θ
• Het = [1-(1/2 Ne(v) )] Het-1
Genetic gain
• Expected genetic gain is computed based on
fertility of orchard parents and breeding
value of trees.
• ΔG = Σ Gi pi
Fertility status
• 18% ( 35 trees) of selected trees were fertile
• No correlation between tree growth and
fertility (r = 0.057)
• High correlation between male and female
fertility (r = 0.981)
• Greater variation in seed output than in
pollen production between trees
Variation in A
Fertility type
Selected 70 pollen
35 trees parents
Male
15.8
10.2
19.3
19.3
Female
17.4
16.3
Av tree fertility
8.2
6.9
Constant seed collection
1
1
Equal fertility
Varying fertility
Gen 1 Gen 2 Gen 4 Gen 6
Gen7
Θ
0.059
0.097 0.172
0.240
0.273
Ns
8.532
5.135 2.910
2.080
1.834
GD
0.941
0.903 0.828
0.760
0.727
Constant seed collection
Gen 1
Gen 2
Gen 4
Gen 6
Gen7
Θ
0.0294
0.049
0.087
0.124
0.142
Ns
17.007
10.230 5.738
4.031
3.521
GD
0.971
0.951
0.876
0.858
0.913
Extra male parents
Gen 1
Gen 2
Gen 4
Gen 6
Gen7
Θ
0.0293
0.068
0.140
0.207
0.239
Ns
17.065
7.365
3.571
2.416
2.096
GD
0.971
0.932
0.860
0.793
0.761
Altering fertility status
• Constant seed collection –lowers Θ by 92%
in 7th generation and Ne(v) is twice that of
existing fertility. Minimum loss in diversity in
each generation
• Extra pollen parents – 14% reduction in Θ in
7th generation. 4-7% reduction in loss of
diversity from existing fertility.
Coancestry variation in different fertility conditions
0.3
varying fertility
0.25
0.2
Constant seed
collection
0.15
Equal fertility
0.1
Extra pollen parents
0.05
0
Gen 1 Gen 2 Gen 3 Gen 4 Gen 5 Gen 6 Gen 7
Generations
Impact of fertility status
• Important role as breeding value as it transfers the
genes to the seed crop.
• Fertility in trees varied from 0-20% (0.005% if trees
had same fertility)
•12 most fertile trees
produced 81% of gametes
•A=17.4 results in high
genetic erosion (Nr drop
from 4.3% to 0.9%) in 7th
generation)
Emphasis in first generation
seed orchard of exotics
• Initiates domestication in a new location
• Lower the values of A to prevent genetic
erosion ( 17.4 > reported value A=9.32)
• Enable random of maximum trees of known
genetic potential.
• Limit equal seed collection to genetically
superior mothers and provide adequate male
parents to enhance the gene diversity.
Fig. 1. Pollen production in Eucalyptus tereticornis
seed orchard
Helenvale 10%
Helenvale
Mt Garnet
M t Garnet 17%
Cardw ell
Kupiano
Orobay
Local 51%
C ardwell 2%
Kupiano 3%
Sogeri Plat
Palmer R
Ravenshoe
Normanby
Orobay 9%
Sogeri Plat 2%
R avenshoe 3%
Kennedy R 2%
N ormanby 1%
Palm er R 0%
Kennedy R
Local
Conclusion
• High levels of inbreeding and
drift may result if precautions
are not taken in a first
generation orchard
• An SSO is ideal in initiating a
breeding / domestication
program as seed can be
produced for different
requirements.
• Additional pollen parents can be retained till selected
trees contribute seed.
• Paclobutrazol can be used to enhance flowering.
Paclo application
in E.camaldulensis
Paclo application
in E.tereticornis