Seed Orchards in Development

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Summary This paper reviews the role of seed orchards as

output systems for genetic improvement programs. In this

paper, technological changes since the 1950s are examined,

with emphasis on recent developments. The need to equate the

type of seed orchard to the type of forestry practiced is recog-

nized, as is the significance of the relationship between seed

orchards and other output systems for genetically improved

material.Keywords: control pollination, genetic improvement program,

management, open pollination, tree breeding.

Introduction

Seed orchards are output systems for genetically improved

material. Although they are not the only means of output, they

are the most widely used. Whether seed orchards remain the

major output system for genetic improvement programs

(Giertych 1987) will depend on the biological and economic

effectiveness with which they are able to transfer genetic gain

from tree improvement programs to the forest. In this paper, Itrace the development of seed orchards by reviewing principles

rather than practices, with particular reference to conifers (see

Faulkner 1975, Sedgley and Griffin 1989).

Seed orchards

Genetic improvement of forest tree species is usually based on

recurrent selection for general combining ability. That is, the

frequency of desirable genes in the population is increased

progressively through cycles of selection and crossing (Shel-

bourne et al. 1989). Because this process involves sexual

reproduction for progeny testing, and because most forest tree

species are established with seedlings, seed has been the tradi-tional output from genetic improvement programs. Seed or-

chards should represent an advancement, both in seed quality

and quantity, over seed stands selected in high quality existing

forests, because they are designed solely for seed production

and are readily replaceable with orchards of more advanced

genetic material. As initially conceived (Larsen 1956), seed

orchards were clonal, but seedling seed orchards have also

been established (e.g., White 1987).

Clonal seed orchards can have considerable limitations

(Sweet and Krugman 1977, Carson et al. 1992, AFOCEL

1992). First, as a result of clonal variability in the quantity of

male and female strobili produced, and the differential timing

of anthesis, individual clones do not contribute equally to the

seed produced; that is, panmixis seldom occurs. Large num-

bers of clones are traditionally used to minimize the impact of

self-pollination and parental imbalance. Second, the almost

inevitable presence of pollen from outside the orchard substan-

tially reduces genetic gains. Third, when ramets of individual

clones are dispersed through the orchard, it is impractical totreat them individually to improve seed yields. Finally, man-

agement costs of orchards with tall trees are very high, and the

time lag in getting genetically improved material to the pro-

duction forest is considerable. For many species, pruning has

not proved particularly effective. As a result of these limita-

tions, modifications were proposed to the design of seed or-

chards and alternatives to seed orchards are being explored.

Alternatives to seed orchards

An obvious alternative to packaging improved genes in seedsis to distribute them in the cells of vegetatively propagated

material. The many techniques of vegetative propagation offer

considerable scope, first to take genetically improved material

directly from the progeny test to the production forest, and

second to increase the output from a clonal or seedling seed

orchard. In both cases, the outcome is a form of clonal forestry,

although true clonal forestry must involve clonal testing

(Libby 1991).

Clonal propagation techniques, which have been improving

in effectiveness both biologically and economically for many

years, may influence the nature of future output systems. In

particular, techniques such as somatic embryogenesis, with

their very high multiplication capacity, may modify the presentrole of seed orchards.

Molecular biology techniques also have implications for

seed orchards. Gene transfer has been accomplished success-

fully in several forest tree species and may become a standard

component of tree improvement programs. Although it is un-

clear how gene transfer technology will be incorporated into

existing breeding programs, the role of seed orchards as output

systems for genetic improvement programs is likely to con-

tinue provided that desirable genes can be successfully trans-

ferred into all, or many, of the individual clones in an orchard.

Seed orchards in development

G. B. SWEET

School of Forestry, University of Canterbury, Private Bag 4800, Christchurch, New Zealand

Received March 11, 1994

Tree Physiology 15, 527--530

1995 Heron Publishing----Victoria, Canada


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Improvements to conventional seed orchards

If seed orchards are to remain the preferred output system, they

need to remain competitive in several areas. (1) They should

maintain the capacity to provide seed that optimizes genetic

gains from the breeding program. This is likely to include

provision for special purpose breeds and regional breeds, for

which only relatively small seed quantities are required (Shel-bourne et al. 1989). (2) They should by economically effective.

Relevant factors of economic effectiveness include the time

required for new-generational breeding material to come into

production, and the cost of establishing isolation zones around

open-pollinated seed orchards. (3) They should produce high

quality output. The traditional Syrach Larsen orchard does

not meet criteria (1) and (2) and thus improvements are needed.

Among the first improvements to seed orchards were at-

tempts to increase seed yields by physical and chemical im-

provements to soils, and by techniques such as root-pruning

and girdling of trees (see papers in Faulkner 1975). Later,

supplemental mass pollination (SMP) was used to increase

seed yields, improve parental balancing and reduce the effectof outside wild pollens (e.g., Franklin 1971). In some

Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) orchards,

SMP was used in combination with water sprays, which delay

orchard anthesis until after the bulk of contaminating outside

pollens have been shed (e.g., Fashler and Devitt 1980). How-

ever, difficulties in applying these and the subsequently devel-

oped gibberellin application technologies (e.g., Pharis et al.

1987) to tall trees led to the development of a range of pruning

and seed collection treatments that are still widely used. The

pruning treatments are more successful in species with a 1-year

seed development habit than in species with a 2-year develop-

ment habit. However, even in species whose seed develops in

1 year, pruning normally removes the most important cone-

bearing part of the crown.

Sweet and Krugman (1977) proposed resolving the limita-

tions of the conventional Pinus orchard by control-pollinating

strobili on 3-m high ramets hedged in clonal blocks. The

hedged ramets allow seed production treatments, pollination

and other management operations to be applied easily from the

ground. Placing ramets in clonal blocks enables treatments to

be applied individually on a clonal basis. Block size can be

adjusted for clonal fecundity. But most importantly, pollina-

tion can be controlled so that specific crosses can be made,

with the potential for increases in genetic gain and for growing

a range of different breeds on the same site.

Control-pollinated orchards

Although most seed orchards have not changed substantially

since 1977, the New Zealand radiata pine (Pinus radiata D.

Don) seed orchards were changed from open-pollinated (OP)

to controlled-pollinated (CP) orchards in 1984 (Carson et al.

1992). Other single species orchards developed with similar

objectives are HAPSOs (hedged, artificially pollinated seed

orchards) and monoclonal orchards, both in Australia, and

micro-orchards (trees planted in clonal rows and hand polli-

nated) in British Columbia and Georgia (Carson et al. 1992).

The use of indoor breeding-halls (e.g., Adams et al. 1992)

offers similar potential. In terms of genetic quality, the CP

orchards are superior to OP orchards, although SMP applied to

individual whorls of flowers is a close substitute. However, CP

orchards have not been widely adopted, possibly because of

problems associated with increased conelet abortion and lower

seed yields. Equally, however, Giertych (1987) has pointed out

that, in many European countries, the major role of seed

orchards is simply to make seed more readily available. Thus,

there may be little incentive to establish CP orchards in many

parts of the world.

Orchard siting

Recently, there has been considerable emphasis on the siting

of seed orchards. There has been interest in transferring or-

chards in harsh climates toward warmer regions, to enhance

quantity and earliness of flowering, seed maturation and isola-

tion against foreign pollen (e.g., Enescu 1987). Long distance

transfers of 1000 to 2000 km have been advocated for the latter

reason (Koski 1987). However, there is increasing evidence for

the existence of physiological aftereffects (Schmidtling 1987).These are effects of the climate at the orchard site on the

climatic adaptability of the seedlings.

The siting of seed orchards has also been used to optimize

flower initiation. Sweet (1975) found that a more than 10-fold

variation exists in cone production across radiata pine forest

sites. For seed orchard management, high cone production and

low vegetative growth is desirable, but little is known about the

climatic and soil conditions under which this occurs.

The use of potted grafts in a controlled greenhouse environ-

ment has been successful for small seeded hardwood species

and some conifers (e.g., Sedgley and Griffin 1989). However,

the significance of physiological aftereffects has not been

widely assessed.

With CP orchards, there is increasing interest in growing

male and female orchards on separate sites. Seasonal earliness

of anthesis then becomes important, because it may allow fresh

rather than stored pollen to be used in a pollination program.

In addition, ontogenetic earliness of flowering is key to the

economic effectiveness of all orchards, because there appears

to be a close correlation between heaviness of flowering and

ontogenetic earliness.

Physical management of orchards

The traditional seed orchard is relatively straight forward to

manage, apart from issues such as graft incompatibility (e.g.,

Copes 1970) and protection against fungal pathogens andinsect pests (Bramlett 1987); however, the management of

hedged orchards in clonal blocks is more complex. Much of

the basic data needed to make effective management decisions

does not exist but, as pointed out by Giertych (1987), the

horticultural industry has considerable experience in intensive

orchard management, much of which is relevant to forest tree

seed orchards.

In New Zealands CP orchards, it has been determined (e.g.,

Arnold 1990) that it is profitable to increase the stocking of

ramets per hectare to the level of a meadow orchard (up to

10,000 ramets per ha). However, optimal meadow orchard

528 SWEET


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stocking, in terms of seed production per hectare or returns per

kg of seed, is not known, and returns from fertilizer, shelter or

irrigation have not been evaluated. A pruning schedule has

been developed for meadow orchards (Sweet 1992). There are

particular difficulties in optimizing yield and financial return

in orchards ofPinus, because pruning in the early years of a

meadow orchard involves a constant trade-off between retain-

ing existing immature cones and sacrificing them with the

prospect of getting more cones in their place the next year.

Quantitatively optimizing rotation age is also difficult.

Chemical management of orchards

Gibberellins A3 and A4/7 have been effective in enhancing the

flowering of several genera and species in the Cupressaceae,

Taxodiaceae and Pinaceae (Pharis et al. 1987). Paclobutrazol

has also been identified as a reliable tool for increasing flower

bud production in a range of species (AFOCEL 1992). In

some orchards, chemical pollen emasculation is important.

Because the optimal application time for chemicals is depend-ent on ramet size, clone, season and orchard location, it is

desirable to develop a simple biological model that will inte-

grate these variables (Bonnet-Masimbert and Doumas 1992).

Pollination and pollen management in CP orchards

With CP orchards, the opportunity exists to reduce clonal

numbers and thereby increase genetic gains. In New Zealand,

single parent pollination was initially associated with conelet

abortion and low seed yields per cone. These difficulties have

been overcome by the development of new methods for pollen

extraction, storage and application technology (Sweet et al.

1992, Siregar 1994). Liquid pollination has proved effective inproducing seeds that are larger and have higher germination

capabilities than seed produced from normal (dry) pollinations

(Setiawati 1994).

There is considerable interest in carrying out liquid pollina-

tion without isolation, because it appears to be able to produce

seed of the same genetic quality as obtained with isolation, but

with considerable economic and logistic savings (Sweet et al.

1992). Also, it obviates the large reduction in seed yields per

cone associated with the use of isolation bags (Setiawati 1994).

Physical seed quality

There has been little emphasis in seed orchards on producing

seed of a specific physical quality. Studies in New Zealand

have shown that seed collected from 3-year-old meadow or-

chard ramets is comparable in size and germination capacity

to seed collected from 6-year-old hedged ramets. The size of

orchard seed can be increased by carefully timed irrigation

treatments (Setiawati 1994). Rimbawanto et al. (1988) showed

that by curing cones ofP. radiata in a warm, low humidity

environment, they could be harvested about 6 months before

maturity and matured at a faster rate, which enables seed to be

sown 12 months earlier.

Conclusions

This article has concentrated on clonal seed orchards, but it

should not be overlooked that determining the nature of output

systems is an integral part of planning a breeding program

(White 1987). The decision whether to use clonal or seedling

seed orchards, or polycross seed orchards (Baradat et al. 1992)

must be made on the basis of economic and genetic considera-tions. The principles established for clonal seed orchards are

readily transferable to other types of orchard.

References

Adams, G.W., J.C. Irving and M.S. Greenwood. 1992. Optimizations

of environmental regimes for flowering in an indoor breeding hall

for black spruce, white spruce and Jack pine.In Proc. AFOCEL/IU-

FRO Conference, Bordeaux, France. 1:219--227.

AFOCEL. 1992. Mass production technology for genetically im-

proved fast growing tree species. Proc. AFOCEL/IUFRO Confer-

ence, Bordeaux, France. Vol. 1, 441 p, Vol. 2, 532 p.

Arnold, R.J. 1990. Control pollinated radiata pine seed----a comparison

of seedling and cutting options for large-scale deployment. N.Z.

For., November, pp 12--17.

Baradat, P., C.E. Durel and P. Pastuszka. 1992. The polycross seed

orchard: an original concept. In Proc. AFOCEL/IUFRO Confer-

ence, Bordeaux, France. 1:181--188.

Bonnet-Masimbert, M. and P. Doumas 1992. Physiological approach

to flowering induction in conifers.In Proc. AFOCEL/IUFRO Con-

ference, Bordeaux, France. 1:51--59.

Bramlett, D.L. 1987. Protection of pine orchards in the South-eastern

United States. For. Ecol. Manage. 19:199--208.

Carson, M.J., T.G. Vincent and A. Firth. 1992. Control-pollinated and

meadow seed orchards of radiata pine.In Proc. AFOCEL/IUFRO

Conference, Bordeaux, France. 2:13--20.

Copes, D.L. 1970. Graft incompatibility and union formation on

Douglas-fir. Silvae Genet. 19:101--106.Enescu, V. 1987. Climate and the choice of seed orchard sites. For.

Ecol. Manage. 19:257--265.

Fashler, A.M.K. and W.J.B. Devitt. 1980. A practical solution to

Douglas-fir seed orchard pollen contamination. For. Chron.

56:237--241.

Franklin, E.C. 1971. Pollen management in Southern seed orchards.In

Proc. 11th South. Conf. For. Tree Improv., Atlanta, GA, USA, pp

218--223.

Faulkner, R. 1975. Seed orchards. Forestry Commission Bulletin 54,

149 p.

Giertych, M. 1987. Seed orchards in crisis. For. Ecol. Manage. 19:1--7.

Koski, V. 1987. Long geographic transfers as a possible way of

eliminating pollen contamination in advanced generation orchards

ofPinus sylvestris. For. Ecol. Manage. 19:267--271.Larsen, C.S. 1956. Genetics in silviculture. Oliver & Boyd, Edin-

burgh, U.K., 224 p.

Libby, W.J. 1991. Opening comments.In Proc. Clonal For. Workshop,

Rotorua, New Zealand. FRI Bulletin No. 160, pp 11--12.

Pharis, R.P., J.E. Webber and S.D. Ross. 1987. The promotion of

flowering in forest trees by gibberellin A4/7and cultural treatments:

a review of the possible mechanisms. For. Ecol. Manage. 19:65--84.

Rimbawanto, A., P. Coolbear and A. Firth. 1988. Artificial ripening of

prematurely harvested cones of New Zealand Pinus radiata and its

effect on seed quality. N.Z. J. For. Sci. 18:149--160.

Schmidtling, R.C. 1987. Locating pine seed orchards in warmer cli-

mates: benefits and risks. For. Ecol. Manage. 19:273--283.

SEED ORCHARDS IN DEVELOPMENT 529


4/4

Sedgley, M. and A.R. Griffin. 1989. Sexual reproduction of tree crops.

Academic Press, London, U.K., 378 p.

Setiawati, Y.G.B. 1994. Study of seed yield and physical quality in

Pinus radiata D. Don seed orchards. M.S. Thesis. University of

Canterbury, New Zealand, 152 p.

Shelbourne, C.J.A., M.J. Carson and M.D. Wilcox. 1989. New tech-

niques in the genetic improvement of radiata pine. Commonw. For.

Rev. 68:191--201.Siregar, I.Z. 1994. Management of pollen, pollination and gibberellin

A4/7in Pinus radiata D. Don seed orchards. M.S. Thesis. University

of Canterbury, New Zealand, 144 p.

Sweet, G.B. 1975. Flowering and seed production.In Seed Orchards.

Ed. R. Faulkner. Forestry Commission Bulletin 54, pp 72--82.

Sweet, G.B. 1992. Seed orchard research and management in the

1990s----a New Zealand case study.In Proc. AFOCEL/IUFRO Con-

ference, Bordeaux, France. 2:65--72.

Sweet, G.B., R.L., Dickson, B.D. Donaldson and H. Litchwark. 1992.

Controlled pollination without isolation----a new approach to the

management of radiata pine seed orchards. Silvae Genet. 41:95--99.

Sweet, G.B. and S.L. Krugman 1977. Flowering and seed production

problems----and a new concept of seed orchards.In FAO/IUFRO 3rdWorld Consultation on Forest Tree Breeding, Canberra, Australia.

2:749--759.

White, T.L. 1987. A conceptual framework for tree improvement

programs. New For. 4:325--342.

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Seed Orchards in Development