"Optimum numbers of clones "Optimum numbers of clones

in seed orchards “in seed orchards “

Raleigh Feb 7, 2003 Raleigh Feb 7, 2003 

Dag Lindgren

Department of Forest Genetics and Plant Physiology

Swedish University of Agricultural Sciences

S-901 83 Umeå, Sweden

ReservationReservationAt this moment I am not going to discuss the most relevant question; to what degree each

clone should be represented (unequal proportion deployment. Clone number is easier to understand.

And do not expect me to reveal the secret, why we need diversity. I do not have the answer, just some speculations. Neither time permits to go in depth, I will focus on the number of clones in seed orchards.

This is a study which started <two months ago. Thus I am very interested in listeners input.

More provocative question: “Is not one clone enough?”

One clone would be pollinated by lots of fathers outside the seed orchard. A one clone seed orchard would deploy more diversity than found in half of US current pine plantations!!!

How many clones…?One of the first and most evident questionsOne of the most important, “key” questions It is easy for a manager to adapt to the

answer, the difficulty is the answerThe number is used for control, certification

and monitoring

Number of clones in seed orchards Two previous studies has the agenda in the title: Lindgren-D

1974. Aspects of suitable number of clones in a seed orchard (proceedings); Hattemer-HH et al. 1982. Klonanzahl forstlicher Samenplantagen und genetische Vielfalt (in German).

Few citations (most self-citations), others have not tried to think much or deep.

I have not found a in depth discussions in a journal paper. Surprising, considering the importance of the subject!

So, I decided to make a new study during Xmas holidays. Even if the exact answers I try to give are not accepted, at least I go through the issue a bit more systematic.

Table 3. Average sizes and clone numbers in clonal seed orchards (Kang et al., 1998)

Seed orchard location

Species Number of S.O.

Avg. size of S.O.(ha)

Avg. N Avg. # of ramets/S.O.

Finland P. sylvestris 179 15.3 137.3 4,098

P. abies 25 10.9 75.4 3,182

Sweden P. sylvestris 22 14.5 79.8 4,614

P. abies 11 11.2 71.2 2,713

Korea P. koraiensis 13 7.0 70.4 2,689

P. densiflora 8 13.6 94.0 5,454

Average 12.1 88.0 3,792

Seed orchard size and clone number (Kang et al 2001)

Pines in south US (McKeand et al. 2003, in press)

Rough average 24 clones in lob SO 42 clones in slash SO

6 SO with only 5-10 clones

First seed orchards For early seed orchards with untested clones, many clones

may be right. They differ little in expected breeding value Its easier to get support for selecting plus trees and testing

clones if they are in seed orchards. Thus many clones in seed orchards was a way to get tree breeding financed.

Material for grafting may sometimes be limiting. More plus trees means more material.

Seed orchards functioned as clonal archives Thus, there have not been strong reasons to argue for low

numbers until recently

A model which considersGainBreeding value of available candidatesGene diversitySelfingFertility differencesPollen contaminationClose neighbor pollination

Gain

AirG G = genetic gain

i = selection intensity

r = correlation between measured “height at 6 years at some test environments” and goal “value for forestry over a future range of plantation sites”

A variation in desired goal character (CV additive)

r and A are constant, gain depends only on selection intensity

The fewer selected, the higher the gain!

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3

0.00.20.40.60.81.0Selected proportion

Se

lec

tio

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ns

ity

Scenarios

Swedish Scots pineAmerican loblolly pine

Scale and chosen entries

AirG G BV related to average of candidates in “value for forestry”

i = i(n,300) n clones selected from 300 candidates

r = 0.7 for Sweden

r = 0.8 for America (“older” and more uniform field trials and the “value for forestry” refers to a closer future)

A = 0.125

Diversity

In my previous seminar in this series (January 17), I suggested diversity to be quantified by status number (or equivalently group coancestry or gene diversity).

Effective population size of an orchard is best described as foreseen status number of the seed orchard crop.

It should be diversity of some value for the seed orchard manager or forester

Evolutionary potential is not such a criterion, that is National or regional problem. Seed orchard designs are rather unimportant for this problematic.

Allele richness has a value only if it can save the stand, alleles in a frequency below 15% cannot save the stand, thus no argument for high clonal number.

Similarity with natural conditions could be an argument. From a fine-grained structure (half sib groups) point of view, seed orchards with more than 25 clones form a less natural population structure than a natural forest.

Non-overlapping flowering can be a problem if less than say 6 clones.

Public Relations, green certification etc. has an evident market value, and staff is also more happy if operations are sustainable and in reasonable harmony with environment. From this point of view it is a large advantage if the situation appears as monitored and controlled. Status number (=gene diversity) considerations contributes to filling that function.

Diversity in a plantation

  Genetic diversity in is likely to favour biological production:

• One genotype demands the same things at the same time, several use the site resources better!

• In a mix another genotype may take over the ecological space left by a failed one.

• A disease spreads faster in a uniform crop.

This expectation has generally been confirmed by a number of experiments with different agricultural crops

Too much diversity in plantations?!

Most crop- and many forest managers do not like diversity,

Uniform trees = better economy, more valuable crop, simpler management;

Genetic superiority of the best clones is much larger than the loss in biomass production by uniformity;

The current demand for diversity in intensively managed forests is – in my opinion - unreasonable expensive in lost future gain;

Most of the benefits with diversity is obtained by five genotypes instead of an infinite number.

Gives the probability for interaction between related tree, e.g.

competition for resourcescomplementing shortcomingsmating (inbreeding in plantations)disease or pest “jump” to the same

substrateThus the “best” quantification

Group coancestry (Status number)

Quantification of low diversity lossA high group coancestry can be assumed to

cause production losses, calamities and more severe epidemics, but how much?

The loss is proportional to group coancestry, but what is the coefficient? I call it DivCoeff. The loss (on the same scale as gain) is

Loss=DivCoeff*

Value of DivCoeff? This Monday Steve McKeand (et al 2003) said 59% of

all loblolly is deployed as half sib family blocks and no problems reported! 5% loss by =0.14 (Kang et al 2002) would be observed, thus DivCoeff<0.35!

Many experiments and some forestry with full sib families. 10% loss by =0.25 would be observed, thus DivCoeff<0.4!

Many experiments with monoclone plots and some clonal forestry. 10% loss by =0.5 would be observed, thus DivCoeff<0.2!

Mixes of agricultural lines (=0.5) probably 2.5% superior to pure lines (=1), thus DivCoeff=0.05!

DivCoeffSwedish scenario DivCoeff = 0.4American scenario DivCoeff = 0.2 Difference as south US get more

experience with low diversity forestry, less worries, less restrictions, shorter rotation times, less “Nature” (industry forestry replaced cotton, not old growth)

Gain and gene diversity are generally in conflict and must be compromised

0.0

0.2

0.4

0.6

0.8

1.0

1.2

0 20 40 60 80Number of clones

Gain

Diversity

Sibling coefficient Trees give rise to different amounts of seed and

pollen. Can be expressed by sibling coefficient, ,

(probability that seedlings share a parent, Kang 2001)

Consequences of a high : Less gene diversity (more relatedness) More selfing

Value: =2 (Kang et al. in press)

Related clonesNo related clones in the model; A few related clones will cause negligable

inbreeding depression, but reduce gene diversity rather considerable;

I suggest: it may sometimes be worth considering to have fewer clones rather than related.

Selfing Pollen from the ramet itself (10% pollen) Pollen from other ramets of the same clone (40%

pollen)*(sibling coeff)/(clone number) Not the same clone in the close neighborhood

(10% pollen) Compared to outcrossing, selfing pollen is less

efficient (dead zygotes because of genetic load). Reduction in seed yield and yield of plantable

seedlings to 0.3 for Swedish, 0.1 for America Selfed seedlings reduce “forest value” 50%.

Pollen contaminationDecreases gain Increases gene diversityEstimate: 40% pollen (that’s almost 50% of

seeds)Estimate of breeding value of aliens: 0.94

for Swedish; 0.85 for America (America more advanced, but even contamination “improved) (average candidate =1)

“Goodness” of seed orchard

SCCSOOutcNeighbSelf NDivCoeff

GFertFertFertSelfprodFertGB /5.0*1*

2

))12(1)(1(

CSO

NeighbwTreeT Polln

PollSelfEffnPollPollSelfEffFert

)*1(

2)2/1( CS Fert

nN

Goodness, B (“benefit”)=

Just to put into a worksheet!

Results

Paramete

rs

Seedorchardmanager at www.genfys.slu.se/staff/dagl

ResultSwedish scenario: optimal number 16American scenario: optimal number 8Main cause for difference: less problems

with selfing and gene diversity in American scenario

Sensitivity analyses Pollination pattern not critical. Breeding value of

contaminates unimportant. Large contamination favors few clones.

Selfing important. Self-fertility favors many clones.

High potential to get gain favors few clones Many candidates moderately favors many clones The value assigned to gene diversity is a very

important factor, a high value favors many clones.

Optimum seems smooth!

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1.0

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0 20 40 60 80Number of clones

Be

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fit,

ga

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ers

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Benefit

Gain

Diversity