Variation in fertility and its impact on gene diversity in a seedling seed orchard of Eucalyptus...
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Transcript of Variation in fertility and its impact on gene diversity in a seedling seed orchard of Eucalyptus...
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 5-7/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 = 0.5 Σ 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 size (Ne
(v))
• 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 0.125
Expectations of seed orchard RUN
Number of trees
Group coancestry;
=(mi+fi)(mj+fj)ij=pipjij
Status number;Ns = 0.5 /
Sibling coefficient; A = C.V.2+1
Variance effective population size;
Ne(v)=A/2(A-1)
Input measurements Proportion Input I.D
B.V. fi mi pi 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 AFertility type Selected
35 trees70 pollen parents
Male 15.8
19.3
17.4
8.2
1
10.2
19.3
16.3
6.9
1
Female
Av tree fertility
Constant seed collection
Equal fertility
Varying fertilityGen 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 collectionGen 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 0.913 0.876 0.858
Extra male parentsGen 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
0.05
0.1
0.15
0.2
0.25
0.3
Gen 1 Gen 2 Gen 3 Gen 4 Gen 5 Gen 6 Gen 7
Generations
varying fertility
Constant seedcollection
Equal fertility
Extra pollen parents
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%
Kupiano 3%
Cardwell 2%
Mt Garnet 17%
Sogeri Plat 2%Orobay 9%
Palmer R 0%
Local 51%
Ravenshoe 3%Normanby 1%Kennedy R 2%
Helenvale
Mt Garnet
Cardw ell
Kupiano
Orobay
Sogeri Plat
Palmer R
Ravenshoe
Normanby
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 applicationin E.camaldulensis
Paclo applicationin E.tereticornis