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