Low Input Tree Breeding Strategies

Dag LindgrenDepartment of Forest Genetics and Plant Physiology, Swedish

University of Agricultural Sciences, Umeå

SwedenSeptember 2, 2002, China

Scientists’ focus: high inputhigh-input-strategy

high-inputlow-input

Input

Output

Because of training and ambitions the attention is mostly

here

High-input techniques

Genotype testing,

Controlled crosses,

Known pedigrees,

Orchards intensively managed exclusively for seed production,

Grafts for seed production.

High inputScientific rewards and fancy journal

papers,

Collegues’ admiration,

Non-sloppy well organised programs,

The main driving force of human phsyc,

Focus for teaching in schools and textbooks at Universities.

High input and low inputhigh-input-strategy

high-inputlow-input

Input

Output

low-input-strategy

Attention should be here for low-input

strategy

Low input situations

Poor Unstable organisation Local control No specialists Minor program Lower tiers of breeding population (main, but

not elite)

Low-input techniques Selection on phenotypes instead of testing of

genotypes,

No records of tree ID or pedigree,

Wind pollination,

Seed production in stands used for other purposes,

“Cheap” plantations created for future seed production and long term improvement.

Low-input techniques

Thin stands rather intense to get better pollen and take seeds from best trees

But…Depend on predictions of inbreeding, coancestry and diversity replacing pedigree. Predictions may fail…. and are generally not even made yet.

Note that there is no strict limit between high input and low input techniques!

Phenotypic selection No tree identities required,

No computer required,

No strict objective measures required,

Transparent (no black box)

Can be executed immediately in field,

A type of selection forwards,

Can also be called mass-selection,

Similar to how Nature selects, thus sustainable and environmental friendly.

Phenotypic selection Depending on predictions for control of

accumulation of relatedness,

Can be diversity use efficient,

Diversity

0.5

00.50 1

Gai

n

Combined index=estimated BV (maximizes gain)

Phenotypic selection (easy)

Between family(exhausts diversity)

Within family(preserves diversity)

Maximising gain at a given diversity by selection in infinite normal distributions. h2=0.25 and P=0.1

Modified From Lindgren and Wei 1993

Note that phenotypic selection is on the optimising curve, thus no other selection results in higher gain without sacrifying diversity!

Testing is doubtful for low-input breeding

more complicated,

more demanding on temporal and organisational stability,

a considerable long time investment requires trust on that the results would be used,

selection forward (untested) is often found to offer as high gain as selection backwards (means progeny-test doubtful effectiveness),

Progeny-testing often not competitive.

12

18

24

30

4 6 8 10 12 14

Effective number (Ns)

Gai

n Breeding valueestimate

Phenotypic

Restricted selection for Phenotypic and Breeding value (combined index, conciders both individual and family) in a population created by 20 parents with family size 20, h2=0.5. Points correspond to restriction intensity. Simulation (POPSIM).

12

18

24

30

4 6 8 10 12 14

Effective number (Ns)

Gai

n

Unrestrictedbreeding value

estimate

Phenotypic

Balancedselection

Note: Phenotypic selection as good as restricted

selection for breeding value compared at same gene diversity!

Unrestricted breeding value selection gives a higher gain, but at the cost of a lower gene diversity!

Remember: Breeding value is based on a combined index of an individual and its sibs used for selection forwards. It does not refer to parental ranking.

Restricted selection for Phenotypic and Breeding value for several generations One and five generations of selection in a population with a family structure, h2=0.5, family size 20

102030405060708090

100110

0 0.1 0.2 0.3 0.4 0.5 Loss of gene diversity

Gai

nBreeding value Phenotype

5 generations

1 generation

Note Phenotypic selection is compatible also in a

multigeneration program For unrestricted selection for breeding value

the genetic variation get exhausted after a number of generations, and in the long run the gain than with phenotypic selection is higher

However, if breeding population large and heritability not very large, this exhaustion takes long time.

0

10

20

30

40

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7Loss of gene diversity

Gai

nPhenotype Breeding value

5 generations

1 generation

One and five generations of restricted selection in a population with a family structure, h2=0.05, family size 500. Low heritability and large families favor combined index

0

10

20

30

40

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7Loss of gene diversity

Gai

n

After first generation

Unrestricted breeding value

Phenotypic

Balanced

After five generations

Development of Gain and gene diversity over five generations of selection in a population with a family structure, h2=0.05, family size 500 for three selection strategies.

Selection strategiesSelection strategy

Advantages Disadvantages

Balanced Maximises gain per diversity loss, Minimises diversity loss

Low gain progress

Phenotypic Simple and low input. Does not require pedigree documentation. Good gain, limited diversity loss. “Optimal”.

Seems unsophisticated

Breeding value

Maximises early gain progress

Fast diversity loss, gene diversity exhausted

The development over generations in a closed population of 154 teak trees based on their observed fertility variations (Bila et al. 1999)

0.00

0.01

0.02

0.03

0.04

0.05

0.06

0.07

1 2 3 4 5 6 7 8 9 10Generations

Co

an

ces

try

(in

bre

edin

g)

Female and male varies

Female constant

Equal-tree fertility

Fertility variation matters for accumulation of relatedness over generations

Grafted seed orchards not low-intensity

large investment, long-term investment, trust in use of product, large scale (management, pollen), special technical competence required, particular land use, organisational stability over time required, selected fathers, but....

“Gene resource plantation”

Looks and is managed similar to a "normal" plantation,

Limited need of specialised competence and organisational stability,

Multiple use (options for seeds and improvement, wood, conservation...),

Can function as seed collection area,

As “cheap” trees may even be cut for seed collection,

Can be close to local organisation, enterprise and people,

Robust to disasters or neglectance,

Small investment, thus limited loss if interest lost

Optional plant identity, but…,

Seeds for commercial use and replacing can be improved by thinning and by harvesting the best trees,

Renewed by wind-pollinated seeds mainly from the plantation,

Coancestry controlled by predictions, sufficient numbers and seed parent contribution control.

Gene resource plantation

Will "we" be needed? Need to optimise "low-intensity" strategy and

tactics (almost not done yet)

Less control (wind-pollination, unidentified trees etc.) means much more thought and predictions needed

The reduced need of competence is "technical competence and field competence“. Not competence of breeding scientists

Low-input should replace No-input, not High-input