Báo cáo khoa học: "Tree improvement programs for European goals and strategies"

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Review article oaks: Tree improvement programs for European goals and strategies PS Savill, PJ Kanowski Oxford Forestry Institute, Department of Plant Sciences, University of Oxford, South Parks Road, Oxford OX1 3RB, UK Most work concerned with the improvement of European oaks is concentrated on Summary — Quercus robur and Q petraea. Improvement is constrained by limited knowledge of the extent and pattern of genetic variation, the long period to reproductive maturity, levels of seed production rela- tive to demand and difficulties in vegetative multiplication. The goals of improvement activities have focused on straightness, vigor and desirable branching; on wood anatomy, shrinkage, density and color, and susceptibility to problems such as frost cracks, shakes and defoliation. Three aspects of breeding are currently receiving attention: 1) in vitro methods for regeneration, flower induction and genetic manipulation; 2) technologies for clonal multiplication, and 3) elements of classical breeding programs. Recent conceptual and technological advances and greatly increased research activity have raised expectations of genetic progress, which will need to be accompanied by developments in associated topics such as silviculture, pathology and wood science. oak / Quercus / breeding / genetic conservation / improvement Résumé — Programmes d’amélioration des chênes La européens : objectifs et stratégies. plu- part des travaux concernant l’amélioration des chênes européens est concentrée sur Quercus robur et Q petraea. L’amélioration est rendue difficile du fait de la connaissance limitée des variations gé- de la longue période pour atteindre la maturité reproductive, de la quantité de graines pro- nétiques, duites par rapport à la demande et des problèmes rencontrés concernant la multiplication végéta- tive. Les buts de l’amélioration ont été concentrés sur la rectitude, la vigueur et la ramification ainsi que l’anatomie du bois, le retrait, la densité, la couleur et la sensibilité à des problèmes tels que les gélivures, les fissures et la défoliation. Trois aspects de l’amélioration génétique sont actuellement abordés : 1) les méthodes de régénération in vitro, d’induction florale et de manipulations généti- ques; 2) les techniques de multiplication clonale; et 3) les éléments de programmes d’amélioration classique. De récentes avancées technologiques et conceptuelles ainsi qu’une activité accrue de la recherche, ont apporté de nouveaux espoirs d’amélioration génétique qui devront s’accompagner de progrès en sylviculture, pathologie et science du bois. reproduction / conservation génétique / amélioration chêne / Quercus /
establishment of only between 2 and 7.5 INTRODUCTION ha/year of plantations at the typical Ger- man stocking of 10 000 trees/ha (Kleinsch- Of the 27 European species of oak, only 3 mit, 1986). are of major economic significance: Quer- cus petraea, Q robur and Q suber. The first 2 are important components of the for- Goals: breeding objectives ests of Europe north of the Mediterranean and selection criteria region, and their timber is highly valued. We concentrate on them in this paper. The third species, Q suber, produces most of Breeding objectives describe the goals of the world’s commercial cork and is the ba- genetic improvement and selection criteria sis of an important industry, especially in as the traits by which this improvement will be realized (Cotterill and Dean, 1990). In Portugal. theory, breeding goals include all traits of Despite their economic importance, a economic importance; selection criteria comprehensive set of constraints the — usually comprise a more restricted set, long rotations, the delay in the onset of chosen for their genetic control and rela- flowering, uncertainty as to the timing of tionship with the breeding objective. Typi- heavy fruiting (good seed years occur at cally traits which influence size and quality 2-10-yr intervals in most regions), impossi- at harvest are included as breeding objec- bility of storing seed for extended periods, tives and weighted according to their rela- and difficulties in vegetative propagation tive economic importance. Selection crite- have made oaks relatively difficult sub- — ria are likely to include those juvenile jects for geneticists and tree breeders, par- growth, quality and resistance traits which ticularly in comparison to shorter-rotation, can easily be assessed, and are known or more promiscuous and more easily propa- expected to correlate well with mature per- gated species, such as poplars, eucalypts formance. and many conifers. We have assumed that quality timber oak At present, there large-scale are no veneer and sawn wood will production for improvement programs in Europe, due continue to be the primary goal of breeding partly to the limited financial support for Quercus robur and Q petraea. Selection breeding long-rotation hardwoods. Conse- criteria are therefore likely to include fast quently, the many seed stands which do growth, especially during the early stages exist will continue to provide the main of development, straightness and lack of source of reproductive material both for forking in the stem, self-pruning, disease nursery production and direct sowing. resistance and wood quality traits. The They are considered by many to represent latter are probably the most difficult to a considerable improvement over the pre- nominate and include shrinkage and aes- vious situation when none existed be- thetic appeal. Available genetic parameter cause seeds are now harvested from well- estimates for oak are summarized in table adapted, phenotypically superior stands I. They are generally consistent with ex- and, in France at least, seed transfers be- pectations from more comprehensive tween regions are restricted. Even when studies in other species; specific results seed orchards have been established, are discussed below and are dealt with their contribution is limited under current more comprehensively elsewhere in this silvicultural practice: a 1-ha seed stand or orchard will produce enough seed for the volume.
Vigor, form and branching Wood properties Growth rate is usually under weaker ge- In general, wood properties are under rela- netic control than stem straightness, which tively strong genetic control (eg, Zobel and is typically moderately heritable (see, for Van Buijtenen, 1989). Their assessment example, Zobel and Talbert, 1984). Both and manipulation are likely to be important usually sufficiently variable and geneti- elements of programs directed at oak are cally determined to allow substantial breeding and propagation. progress; the relationship between them Nepveu (1984a) determined for Q robur has usually been of more concern to that the width of the earlywood is under breeders. In some species, eg Pinus cari- strict genetic control and the percentage of baea, adverse correlations between vigor vessels in the earlywood under moderate and form have constrained simultaneous control. In contrast, environmental effects progress in both traits (Dean et al, 1986). both of individual tree and year large- — — However, it may be possible to achieve determine the width of the latewood and ly sufficient gains in straightness in the first the percentage of fibres within it. Broad- generations of breeding to relax selection sense heritabilities of wood density and for this trait in subsequent generations, as shrinkage have been estimated by Nepveu with P caribaea (Kanowski and Nikles, (1984b) for Q robur, Q petraea and Q ru- 1989). Data for oak are quite limited. Sig- bra. In all 3 species, they are high for den- nificant improvement in stem form was re- sity, medium for volume shrinkage and low ported by Irgens-Moller (1955) for Q robur for the ratio of tangential to radial shrink- selected in The Netherlands. Clonal vari- age, as detailed in table I. Shrinkage char- ability in terms of vigor and form has been acteristics are further discussed by Nep- estimated in 1-year-old plants from cop- veu (1982, 1990), Deret-Varcin (1983), pice shoots (Nepveu, 1982) and is sum- Eyono Owoundi (1991), Huber (1991a) marized in table I. and Nepveu and Huber (1991).Wood ba- Many branch characteristics are more sic density varies greatly between trees, as influenced by the environment than is do the numbers of rays; these variations stem straightness, and gains made could, it is thought, account for differences through selection are generally much more in shrinkage. modest. However, branch angle and, at In the more continental parts of Europe, least in the case of some tropical pines frost crack in Q robur and Q petraea be- (RD Barnes, personal communication) comes a serious problem and susceptibility branch diameter and distribution are highly may have some genetic component. Cinot- heritable. There is some evidence that ti (1987, 1989a,b, 1990a,b; and manuscript these generalities apply to oaks: many of in preparation) and Cinotti and Tahani the commonly propagated cultivars of (1988) support this contention. In compari- Q robur are raised from seed collected son with sound trees, and amongst other from parents selected for, eg, branch an- factors, frost-cracked individuals tend to gle characteristics (McArdle and Santa- have different grain angles, specific gravi- mour, 1985). In their study, a very high ties, radial and tangential shrinkages, proportion of the open-pollinated progeny moisture contents, rays, proportions of ear- exhibit the required branch angle trait: fas- lywood and a differing proportion of ves- tigiate trees tend to produce fastigiate off- sels in the early-wood. Many of these char- spring, and pendulous trees, pendulous acters are known to have high heritabilities offspring.
and so might eventually be used as selec- basic and technological properties of the tion criteria, but correlations with other ma- wood of oak, and the work now underway ture traits are not yet sufficiently deter- to address this topic should be most use- mined to make their immediate application ful. possible. The breeder’s interest in juvenile- Another defect to which Q petraea and correlations, in terms of the rela- mature Q robur are peculiarly susceptible is ring tionship between selection criteria and and star shake. This has been investigated breeding objective, is complicated in the by Henman (1984) and at the University of case of wood properties by their changes Oxford where Savill (1986) found that trees from juvenility to maturity. Studies to inves- with large vessel cross-sectional areas are tigate the feasibility of juvenile selection for particularly predisposed to shake; Kanow- specific wood characteristics in mature ski et al (1991) reported vessel size to be trees by F Huber (1991 b; and manuscript under relatively strong genetic control and in preparation) and Nepveu and Huber therefore amenable to genetic improve- (1991) suggest a high level of variability ment; and Savill and Mather (1990) discov- between trees for several characteristics, ered that large vessels are often associat- eg, vessel diameter, superimposed on a ed with late flushing trees, providing a substantial increase with age for about the relatively easy way of determining shake- first 20 years. The amount of earlywood prone trees at the time of leaf emergence changes with age; fiber percentages de- in the spring. The prospects for breeding crease with age and, in adult wood, seem against shake therefore seem reasonable. to be affected by climate. The proportion of rays is relatively constant within a tree, but To those less skilled than the French varies greatly between trees. The authors and Germans at growing clean stems of stress the preliminary nature of these re- oak, the problem of controlling epicormic sults, and note that further work will be shoot growth can be serious. This charac- necessary before any strategies for juve- teristic has been found by Mather (person- nile selection can be formulated. al communication) to be under reasonably strong genetic control (table I), and there- Gebhardt et al (1989) have suggested fore amenable to selective breeding. that it should be possible to screen aseptic shoot cultures for resistance to various The significance of wood aesthetics has pests and diseases; however, to our been investigated by Flot (1988), Mazet knowledge, no successful applications of (1988), Janin et al (1989, 1990a,b), Fra- such work have yet been demonstrated. mond (1990), Klumpers (1990), Mazet and Toscano Underwood and Pearce used tis- Janin (1990) and Janin and Eyono Owoun- sue explants to screen for fungal invasions di (1991). Studies by several of these au- in Picea sitchensis and their results sug- thors and others such as that by Scalbert gested genetic differences in resistance et al (1989), provide more basic informa- (Toscano Underwood and Pearce, submit- tion on wood chemistry. Early studies es- ted); although the screening was empirical tablished that light-colored oak is particu- without presupposing any mechanisms, it larly valued by most professional users. may serve as a model for work with oak. Investigations of the wood itself indicated that there are significant correlations be- In an attempt to reduce defoliation of tween color, basic density and volumetric Q robur by insect larvae, Roest et al shrinkage. Results suggest that color char- (1991) have attempted to develop an Agro- acteristics might be used as indicators of bacterium-mediated transformation proce-
northern European oaks is that reported by dure with the aim of transferring Bacillus Kremer et al (1991) who had as one of thuringiensis toxin genes and, consequent- their aims the development, for seed iden- ly of increasing resistance. They achieved tification purposes, of a large-scale genetic apparently induced transformation an map based on variation in both allozyme which, in principle, indicates that the spe- and chloroplast DNA markers. In some re- cies is amenable to Agrobacterium gene gions of Europe, at least, this might be dif- transfer for the ultimate production of ficult because of the long history of plant- transgenic plants. To date, however, they ing and sowing with imported seed which have been unable to achieve regeneration must have confused patterns of natural of shoots and plantlets. variation. Nevertheless, Kremer et al Another approach to reducing defolia- (1991) found that these 2 species maintain tion by insects soon after leaf flush in the levels of allozyme diversity that are among spring is to desynchronize the emergence the highest of any woody species so far of leaves and larvae, and this has been in- studied, but that little differentiation is evi- vestigated by Leffef (1988). It should be dent at the molecular level. possible to select and propagate trees, The results of their work led them to de- perhaps the latest-flushing ones (Jovanov- i&jadnr; and Tucovi&jadnr;, 1975), to minimize this risk scribe Q robur and Q petraea as "broadly sympatric species occupying distinct eco- and that of late spring frost damage. How- logical niches with extensive potential ever, as noted above, such trees are more gene flow between them". Natural intro- likely to be susceptible to shake; different gression occurs between Q robur and breeding populations may be necessary to Q petraea to the extent that van Valen address these potentially conflicting breed- (1976) has questioned "the reproductive ing objectives. species concept" among some oaks. Hy- A few investigators (eg, Harmer, this bridization has been reported in many volume) are working on aspects of the studies, as described by Rushton (this vol- physiology and phenology of oaks. None ume). of this work has yet been framed in strict genetic terms, but it is providing informa- The existence of triploids has been re- corded (Johnsson, 1946; Jones, 1959) in tion which may eventually be of value to polyembryonic individuals. These exhibit oak breeders. superior growth to that of diploid trees (Bu- torina et al, 1983, 1986). Both hybrid and non-diploid types may offer possibilities for STRATEGIES breeding and propagation. Activity in artifi- cial hybridization of oaks is discussed else- where in this volume. The extent and pattern of genetic diversity Provenance and progeny tests Recent advances in allozyme and molecu- lar technologies (see, for example, reviews Substantial differences have been ob- by Brown et al, 1990; Soltis and Soltis, served between provenances of Quercus 1990; Neale and Williams, 1991) have rev- petraea and Q robur in terms of growth, olutionized our ability to investigate the ex- flushing and flowering times, lammas and tent and pattern of genetic diversity within epicormic shoot growth, and bud set a taxon. The definitive work to date on
incompatibilities; and of the small number (Krahl-Urban, 1957; Kleinschmit, 1986). Some of these traits are linked to suscepti- of clones used in most seed orchards re- stricting further selection (Kleinschmit, bility to frost damage and defoliation by in- 1986). These limitations, and the relative sect larvae. Differences in stem form, vari- inflexibility of clonal orchards compared to ation in susceptibility to mildew and other other propagation options, have prompted factors have also been found. However, no a reassessment of their role in many obvious geographical (clinal) trends have breeding programs, including those with been apparent at any test site (Jovanovi&jadnr; oak. We consider below the conceptual and Tucovi&jadnr;, 1975), probably reflecting — framework of genetic improvement as a the long history of plant- at least in part — necessary background to the exploration ing and artificial sowing of oaks in parts of of alternative breeding and multiplication Europe. In Germany, at least, human inter- options. vention has been sufficiently strong to lead Kleinschmit (1986) to conclude that oaks should be tested by stand rather than by OPTIONS FOR OAK BREEDING region. Progeny trials have only been estab- lished relatively recently and results from The tree breeding cycle them are therefore more limited. Plus-tree selection and the establishment of seed or- chards began in Germany in 1949 The process of genetic improvement is (Kleinschmit et al, 1975a,b) and progeny best represented as a cycle; figure 1 tests were subsequently installed with presents one such depiction. The selection open-pollinated families of selected trees. of genetically superior trees and the re- combination of their genes in mating are Given the long rotation period of oaks, in- formation from progeny trials on juvenile- mature correlations will be of particular im- portance to breeding strategies. Seed orchards Clonal seed orchards have been estab- lished in many locations; the earliest substantial ones were those in Germany, progressively established since 1949 (Kleinschmit, 1986). Seed orchards are es- tablished primarily for the production of seed for use in operational forestry; how- ever, the low rate of seed production of oak and the limited supply of seed from all sources relative to demand have limited the utility of seed orchards. There are also the usual problems of different clones con- tributing differentially to the seed crop, due to their different flowering patterns, of graft
the essential elements of any breeding pollinated mating returns optimum genetic program. The means by which the gains gains per unit of time and resources. realized in breeding are transferred to op- Open-pollinated mating is easily achieved erational production are also critical in the and effective where the selected trees can practical application of genetic improve- be isolated from outside sources of pollen. ment. Each of these activities results in the Efficient selection requires information assembly of particular groups or popula- from genetic tests and the development of tions of trees. Although not explicit in fig- a selection index; the necessary genetic in- ure 1, genetic testing of these populations formation is easily obtained from genetic is fundamental to successful breeding. tests and the requisite computer software is easily available and readily applicable. There are a number of choices for each of these key elements of genetic improve- Evidence from breeding programs with ment and its operational implementation. tropical and subtropical species demon- Selection may be based on either pheno- strates that simple, robust and cost- type or genotype: the former is essentially effective means of genetic improvement subjective and relatively imprecise; the lat- are applicable to temperate species, and ter is accurate but demands some genetic we contend that their use is long overdue. information. Mating between selected We now discuss options for the major ele- trees may be unrestricted or limited to par- ments of breeding programs, and their po- ticular crosses. While the latter can be ex- tential application in oak breeding. pected to produce greater gains, it is more expensive and usually takes longer to ac- complish. Multiplication of genetically su- Selection, mating and genetic testing perior material to an operational scale may be based on seed production, clonal repro- We suggest that for each region, whether duction or a combination of the two. defined on a genetic or geographical basis, The particular combination of selection, the elements of efficient breeding de- and multiplication options, and the mating scribed above may best be integrated into physical arrangement of populations and a single physical population, described by genetic tests is described by the breeding Barnes (1986) as the "breeding seedling strategy. The optimum breeding strategy orchard". The implementation of this con- for a particular species and circumstances cept in the breeding of various species, in will depend upon the biology of the spe- environments as diverse as Australia, Flor- cies, its genetic characteristics, the level of ida and Zimbabwe (Reddy et al, 1986; resources available and the objectives of Barnes and Mullin, 1989; Cameron et al, breeding. An objective implicit in most tree 1989) has demonstrated it to be simple, ro- improvement programs is the maximiza- bust and genetically- and cost-efficient. Ka- tion of genetic gain, usually for a number nowski and Savill (1989) proposed its ex- of traits, per unit of time and resources. As tension temperate species and to Cotterill (1986a) noted, tree breeding pro- estimated costs only marginally greater grams have tended to emphasize compli- than those incurred in routine woodland cated mating designs, which are theoreti- establishment and management. cally advantageous but practically difficult In essence, application of the breeding and expensive, at the cost of efficient se- seedling orchard methodology involves the lection. Further, Cotterill (1986a,b) demon- strated that a combination of genetically establishment of genetic tests of the spe- effective selection and simple, open- cies of interest, the assessment of these
breeding population to enlarge the base of tests for genetic information, the use of existing seed orchards. He also suggested that information to select genetically super- the development of both macro- and mi- ior trees and progressive thinning of the cro-propagation technologies for clonal test to form an orchard for the production production, and it is to these elements of improved seed. Efficient and effective of operational genetic improvement that we selection, using index (eg, Baradat, 1989; Cotterill and Dean, 1990) or BLUP (best turn. now linear unbiased predictor) methodologies (White and Hodge, 1989) and relatively short generation intervals are essential to In vitro regeneration its success because of the smaller genetic and clonal multiplication gains made with each selection cycle when using simple mating designs. Al- Propagation via in vitro plantlets or cuttings though Barnes’ original concept was based allows the multiplication of superior individ- on the establishment of seedlings, vegeta- uals or families; it provides an essential tive propagules could be used if neces- means of multiplication in circumstances sary. Similarly, the outstanding individuals such as those commonly found in oak, or genetically improved families generated where seed production is inadequate for by breeding may be vegetatively propagat- operational requirements. Successful veg- ed; this may be particularly important for etative propagation of most trees, including many oak species, in which seed produc- oaks, must be cheap and depends upon tion is limited. Details of management re- the development of the right growing medi- gimes for breeding seedling orchards of um and the degree of juvenility of the ma- subtropical species are well documented terial used. As with many woody species, elsewhere (eg, Barnes, 1986; Barnes and propagation from trees more than 6-8 Mullin, 1989); adaptation for temperate years old from seed is difficult, necessitat- conditions should not be too problematic, ing rejuvenation. Large differences be- as Cameron et al (1989) have demonstrat- tween clones in terms of rooting success ed. In summary, the breeding seedling or- and subsequent growth exist. Coppice and chard methodology offers the advantages epicormic shoots are the most amenable of genetic improvement for little more than sources of material (Harmer, 1988; Harmer the cost of woodland establishment. In- and Baker, 1991). deed, we are currently establishing such orchards of Fraxinus excelsior in Britain on Although micropropagation has the ad- this basis. vantage of high multiplication rates over short periods, it has a high requirement for Our approach is consistent with relatively skilled labor and micropropagat- Kleinschmit’s (1986) proposed revision of ed plants can be very expensive in com- classical breeding methods as applied to parison to those produced from seed or oak. He concluded that more efficient prop- cuttings. A degree of automation is there- agation techniques are needed if genetic fore desirable, especially for inducing gains are to be transferred to field applica- branching in embryo cultures and for re- tion and advocated a number of strategies plenishing nutrients without subculturing. to overcome the limitations of clonal seed Systems have been developed in The orchards as the multiplication population. Netherlands by Vermeer and Evers He therefore proposed the establishment (1987a,b), which are successful both with of seedling seed orchards with families of Populus and Quercus cultures, and these orchard origin, using 200-500 trees per
have the potential for wider commercial genome increases, the prospects for wid- application will become apparent, as application. er Peacok (1989) has discussed in general Regardless of the propagation method- terms. ology, maintenance of genetic diversity is essential; relevant considerations have been well summarized by Burdon (1989). Seed production and storage The risks of limiting production to relatively few genotypes are accentuated by the long rotations under which oaks are In most parts of Europe, oak seed produc- grown, and emphasize the need for multi- tion is characterized by occasional years of plication of a minimum of around 20 geno- surplus, interspersed by several years with types from each breeding population (Lib- little or no seed. Until recently, few at- by, 1982; Burdon, 1989). tempts at storing acorns for long periods have come to much. Acorns are recalci- trant seeds which lose their capacity to Flower induction, grafting germinate if too dry and do not survive and gene transfer very low temperatures. However, Evers et al (1990), Muller and Bonnet-Masimbert (1984), and Suszka and Tylkowski (1980) at artificial induction of flowering Attempts have demonstrated that they can be stored which have worked well in many other — with acceptable levels of germination over are being developed in Ger- species — 3 winters (ie 30 months) if they are main- many. They involve treatment with growth tained at a temperature of -1 °C and at a regulators or grafting to selected rootstock moisture content of not less than about genotypes. Gebhardt and Goldbach 40%. They require soaking in water at 41 (1988) think that, as with, for example, ap- °C for 3 h before storage to prevent dam- ples and cherries, it should be possible to age by the fungus Ciboria batschiana. find rootstock genotypes which induce ear- ly fruiting and cause dwarf growth in graft- ed seed orchards. QUERCUS SUBER, MEDITERRANEAN The establishment of clonal orchards or AND OTHER OAKS conservation banks requires development of reliable grafting techniques, which are There is little in the forestry literature on now reasonably established, and have European oaks other than Q robur and been described by Chalupa and others in Q petraea; Q suber and Q ilex are the oth- this volume. The technique of micrograft- er species which have received more than ing shoots in vitro from shoot-tip cultures passing attention. onto seedlings, and vice versa (Gebhardt and Goldbach, 1988) could be valuable if it is successful with oaks. Quercus suber The rapid development of techniques in molecular genetics suggests that they could, in time, be used in oak breeding Despite its importance and several exhor- programs. In the short term, it seems like- tations as to the necessity of research, ge- ly that the focus of such work will remain netic improvement of cork oak received lit- on pest and disease resistance. As our tle attention until 1988 (Sardinha, personal knowledge and understanding of the oak communication). Natividade (1954, 1958)
described cork oak as exceedingly variable cies’ mating system and found that trees in terms of vigor, form and the characteris- not necessarily pollinated by neigh- were tics and production of cork tissue. It there- boring individuals, but by those which are fore appears well suited to selective breed- phenologically synchronous and which are ing; Natividade (1954) proposed a predominantly pollen producers. As this breeding program, detailing traits which temporal isolation reduces the effective should be sought or discouraged, both for population size, they proposed that it also the production and technical properties of contributed to the current population struc- cork, and the acorns, which were much ture. valued as animal feed. He suggested the establishment of clonal seed orchards, in- vestigations into vegetative propagation CONSERVATION OF GENETIC and other now familiar methodologies for RESOURCES improvement. Current work aims to devel- op breeding methodologies, particularly The consequence of erratic seeding and those which will take account of genotype- inability to store seed has, for centuries, environment interactions. This approach been a major reliance on planting with im- has involved characterization of the trees ported stock, with the associated risks of and selection of plus trees (especially for genetic erosion. An extreme case is that of cork quality) in selected stands; investiga- Great Britain, where it is now virtually im- tions into the genetics of cork production; possible to be certain that any oak is of na- estimation of the correlations between cork tive origin. In areas less contaminated with quality and leaf enzyme systems and the foreign seed, such as the Pyrenees development of grafting and macro- and (Cantegrel, 1984), strong concerns have micropropagation techniques. Several pa- been expressed about the possible degen- pers have already emerged from this work, eration of local races and the need for their including those by Nobrega et al (1990) on conservation. Both methodologies for seed isozymes, and Roldao (1990) and Roldao storage or plant preservation and identifi- et al (1990) on vegetative propagation. cation of the nature and pattern of genetic Current research in Portugal reveals that variation are necessary for effective con- many of the issues implicated in the genet- servation measures. ic improvement of cork oak are similar to those of Q robur and Q petraea described The results of recent work on conven- above. tional seed storage have been described above. Jörgensen (1990) reported results of attempts to find a means of conserving Quercus ilex genetic resources at very low tempera- tures. Gebhardt et al (1989) proposed the conservation of shoot-tip cultures at low Yacine and Lumaret (1988, 1989) used al- temperatures, but no such work has yet lozyme markers to investigate genetic di- been reported. versity in Quercus ilex over various parts Early results of the INRA-Bordeaux pro- of France, including Corsica, and North Af- gram, which is investigating oak genetic di- rica. They found substantial between- versity, have been reported by Kremer et population, but little within-population, di- al (1991); this program should provide versity, which they suggested resulted much of the information necessary for ef- from a number of evolutionary and anthro- fective genetic conservation. pogenic factors. They also studied the spe-
CONCLUSION ACKNOWLEDGMENTS We thank the many respondents to our request It is apparent that any program for the ge- for information on current work in Europe; were netic improvement of oaks is likely to be of it not for their helpful responses, this paper a much more long-term nature than similar could not have been written. We also thank two work for shorter rotation, less recalcitrant anonymous reviewers for their constructive com- species such as poplars. However, both ments. techniques and understanding have ad- vanced considerably in recent years and REFERENCES the immediate challenge is to continue the initial research work and consider the means by which it can integrate with prac- Baradat P (1989) Amélioration Génétique des tical forestry. Arbres Forestières : Eléments Méthodolo- giques. INRA-Recherches Forestières, La- Given the resource constraints of most boratoire d’Amélioration, Pierroton 33610 and individuals involved in fo- agencies Cestas, 204 pp the practical application of tree restry, Barnes RD (1986) Multiple population tree breeding depends upon simple, robust, breeding in Zimbabwe. In: Proceedings of the cost-efficient means of genetic improve- IUFRO Joint Meeting of Working Parties on ment. Fortunately, genetic theory is con- Breeding Theory, Progeny Testing and Seed Orchards. Williamsburg, VA, 13-17 October sistent with these 2 requirements. We be- 1986, 285-297 lieve that the two keys to this synthesis Barnes RD, Mullin LJ (1989) The multiple popula- are: 1) the integration of all key elements tion breeding strategy in Zimbabwe-five year of the breeding cycle in a single physical results. In: Breeding Tropical Trees: Popula- population, which serves as a genetic tion Structure and Genetic Improvement Strat- test, selection base, and source of im- egies in Clonal and Seedling For-estry (Gib- proved seed and propagules, and; 2) the son GL, Griffin AR, Matheson AC, eds) Oxford Forestry Institute, Oxford, UK and Winrock In- use of resource-efficient multiplication ternational, Arlington, VA, 148-158 methodologies. The breeding seedling or- Brown AHD, Clegg MT, Kahler AL, Weir BS chard approach is ideally suited to ad- (1990) Plant Population Genetics, Breeding dress the first requirement and we think and Genetic Resources. Sinauer Associates, that it can be successfully adapted to Sunderland, MA, 449 pp oaks. Its adoption adds few costs to those Burdon RD (1989) When is cloning on an opera- of conventional woodland establishment tional scale appropriate? In: Breeding Tropi- but can be expected to deliver substantial cal Trees: Population Structure and Genetic genetic gains. The considerable work al- Improvement Strategies in Clonal and Seed- ling Forestry (Gibson GL, Griffin AR, Mathe- ready under way on propagation tech- son AC, eds) Oxford Forestry Institute, Ox- niques gives us confidence that satisfac- ford, UK, and Winrock International, tory multiplication technologies will soon Arlington, VA, 9-27 be widely available. Progress towards the Butorina AK, levlev VV, Muraya LS (1983) Cy- more widespread and effective implemen- togenetics of the spontaneous triploid of oak tation of oak genetic conservation and im- (Quercus robur). Genetics 4, 647-658 provement therefore depends, in part, Vetkasov BK Butorina AK, Pletminceva TI, upon continuing research efforts, but (1986) Cytogenetic characteristics of pheno- equally upon our ability to communicate typically superior oak trees (Quercus robur) from ship Forest. Dokl Akad Nauk SSSR its prospects and promise to forest man- 298, 1241-1244 agers.
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