Genetic diversity and seed orchards

Dag Lindgren

2006-03-20

Uniform plantations – a good thing?

Genetic diversity is a problem. A uniform crop:

• is easier to manage;

• is better paid;

• is preferred by customers;

• offers higher genetic gain.

Genetic diversity could be favourable for biomass

production!• A single genotype requests the same thing at the same

time. A mixture may use the ecological space more efficient;

• A disease or pest may adapt and spread faster in a uniform crop;

• If one genetic component fails, another may take over the free ecological space in a diverse crop;

• A genetic diverse crop probably has a more stable production over a range of environments, is more repeatable and fails more seldom;

Genetic diversity is profitable and politically correct

• Genetic diversity is politically correct and good PR.

• Genetic diversity facilitates green certification which has market value.

• Genetic diversity results in immediate economical return as it improves sales.

• It is likely e.g. some spider species can be identified which marginally benefits from genetically diverse trees within species.

Perhaps too much diversity in natural stands to constitute good

seed sources for planting?

• In nature only one seed among a million develops into a mature tree. Room for “natural selection” to improve the trees;

• Forestry plants in wide spacing and avoids pre-commercial thinning. Most seeds become planted seedlings and many planted seedlings become valuable trees;

• Therefore the natural genetic diversity may be unpractical large for modern forestry.

• People fear monoclonal GMO forests! This fear is irrelevant for seed orchards.

• However, seed orchards are less efficient than they could, as they are not a fancy futuristic research priority.

How are seed orchard crops different from “natural seeds”?• Physiologically better seeds;• Parents are selected;• Little mating among relatives;• Other ramets of the same clone

cause selfing;• Better defined and more

reproducible.

Suggested seed orchard impact

• A limited number of plus trees will get a lot of descendents;

• The trees in the future forest will be similar;

• The forest will grow faster.

The most important impact of seed orchards on environment and

diversity is more productive forests!• Intensive forestry causes environmental impact, not the

diversity of seed orchard crops!;• Intensive forestry uses the site efficiently, thus less

room for others; • If genetic diversity makes forests more fail-safe, that

strengthens the environmental impact of intensive forestry;

• Much of the impact of the intensive forestry could be positive. Productive profitable forests facilitates creating reserves and financing environmental actions; forests sequester carbon dioxide; forestry can be seen as sustainable recycling of water and air;

• Improved material is an important component for intensive forestry. Seed orchards stimulate more intensive forestry!

Seed orchards have yet little impact on Sweden

• 50 % of planted spruces and 80 % of planted pines are from seed orchards;

• Some area never regenerated on purpose (15%?);• Intentional ”Natural” regeneration 35%;• Natural ”volunteers” in plantations (20%?);• Many fathers unknown (40-50%);• Only 1/3 of the genes in the forests established 2005 are

from selected trees• The average age of a forest at final harvest is 110 years

and seed orchards have been important only for 30 years. • As seed orchards has little impact on forest, they also

have low impact on genetic diversity.

Genetic diversity is the backbone of evolution !

But this is irrelevant! Seed orchard crops are not central for evolution, they are more or less planned as dead-ends. The long term breeding is more important for the far future.

Rare gene variants can have a role in evolution, but not in production!

Source: Wei 1995

Variance among few catches most of all variance

A small sample is as variable as the full population!

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Sample Size

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Seed orchard crops are diverse!

•Phenotypic selection of plus trees uncertain, preserves diversity;

•Marker gene measurements indicate that seed orchard crops can be more diverse than stand seeds;

•In a small piece of a natural forest, trees are as related as trees from a seed orchard plantation;

•Seed orchard clones are recruited from a large area, which favours diversity compared to stands;

•Pollen sources outside the seed orchard favours diversity;

•There are many clones in the current seed orchards;

•Thus a stand from a seed orchard is as diverse as a natural stand!

Scots pine seed orchard; Suokanta, Finland

Location of the seed orchard

Locations of the plus treesUtilization

area

The new orchards

Modern seed orchards will be different from old:• Selections will be tested and consider

performance of relatives (progeny), thus have known breeding value;

• Fewer clones will be selected;• I will discuss suitable clone number below;• Relatives will be selected, but to a neglectable

extent.

Seed orchards with selected tested clones

The best clones will be similar in estimated breeding value for the selection criteria, that does not mean they will be very similar;

• The selection index selected for is a combination of characters, the individual characters will be more different than the selection index;

• Selection based on young performance, selections will be more different both earlier and later;

• Different batches of selections tested under different conditions will be combined;

• One quarter of the parents to the seeds not in orchard;• Even if characters look similar, the “cause” is probably different genes

in different trees;• Just a few economically important characters affected by selection;• Most of the genome will be unaffected;• The reduction is just for BV, not for e.g. dominance; • Most of the initial variance is recovered at mating, thus loss by

selection of parents has limited importance for their progeny;• My guess is that the variance in future seed orchard crops will be at

least as wide as in current stand seeds even for economically important factors.

Impact on landscapeCurrent Swedish plans extrapolated a century ahead may

lead to landscapes, where gene mass origin from few ancestor trees. An educated guess…..

Share of gene mass Ancestor trees

20% 10

20% +20

20% +100

40% millions

Number of clones in a seed orchard

The most common agenda when talking about genetic diversity or discussing legal constraints

Country Species Average Number of Clones

Finland P sylvestris 137

P abies 75

Sweden P sylvestris 80

P abies 71

Korea P koraiensis 70

P densiflora 94

Number of clones in current seed orchards (source: Kang et al 2001)

Current seed orchards has many clonesThere were reasons to use many clones in seed

orchards until now:• The plus trees was selected based on their

appearance in the forest and differ little in expected breeding value;

• Its easier to get support for selecting plus trees and testing clones if they are in seed orchards. Many clones in seed orchards helped to get tree breeding financed;

• More plus trees means more material for production of grafts;

• Seed orchards functioned as clonal archives;• Many clones reduces selfing and appears safe;• Sometimes genetic thinning was planned.

Pines orchards in south US

(McKeand et al. 2003)

• Rough average: –24 clones in lob SO;

–42 clones in slash SO;

• 6 SO with only 5-10 clones.

Optimal number study

Lindgren and Prescher (2005)

Considered factors:• Genetic gain• Genetic diversity• Reasonable variations in ramet number and

fertility• Pollen inflow (pollen contamination)• Selfing

Swedish pine and estimates used unless something else stated!

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Fewer clones → higher gain!

Gain and gene diversity are in conflict!

0 20 40 60 80Number of clones

Gain

Diversity

Positive diversity

• Diversity is assigned a positive value.

How to put a value on diversity?Observations:1. Mixes of agricultural lines are on average a few percent superior to pure lines!2. 59% of all loblolly in the US is deployed as half sib family blocks and no problems are reported (McKeand et al. 2003)! 3. Full sibs in many experiments and some forestry, few problems reported!4. Monoclonal plots in many experiments and some clonal forestry, few problems reported for non extreme cases.A disadvantage in the magnitude 10% would be noticed and reported for cases 2-4. The absence of many and substantial reports supports a bound for the impact of diversity.

Selfing

• Selfing becomes an important consideration if there are few clones;

• A reason for a high clone number!• Selfing can be slightly reduced if ramets of

the same clone are not placed adjacent.

Number of clones - results

• Swedish scenario: optimal number 16;• Rather robust, thus 12 or 25 is not critical;• Too few is more risky than too many. Safety bids 20 (example of “risk”:

pollen contamination problem solved);• The estimates may be slightly conservative, perhaps revised to 12 in

some decades;• It is tolerable with 10, but a higher number is probably better.• Too high for production may still be right for “economy”!• Future seed orchards will use clones in intentional different

proportions (more of the better), in that situation a slightly higher clone number (25) can be used.

• American P taeda scenario gave optimal clone number 8 (more reliable field testing and much experience of half sib forestry.

More?

More about the subject can be found by browsing: http://www.genfys.slu.se/staff/dagl/

Dag Lindgren’s email is Dag.Lindgren@genfys.slu.se

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