Báo cáo khoa học: "A critical review of larch hybridization and its incidence on breeding strategies"

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Review article A critical review of larch hybridization and its incidence on breeding strategies L.E. Pâques INRA, Station dAmelioration des Arbres Forestiers, Centre de Recherches Foresti6res, Ardon, F-45160 Olivet, France (received 28-2-1988, accepted 26-10-1988) Summary &horbar; Hybrid larch (Larix X eurolepis Henry) superiority over the parental species (Larix decidua Mill. and Larix kaempferi (Lamb.) Carr.) has been described by many tree breeders. This superiority concerns not only growth characteristics but also several economically important traits. In the literature, there is some ambiguity regarding the 3 following concepts : hybridization, hybrid superiority and heterosis. In particular, the superiority of hybrid larch has been claimed in many studies as due to heterosis. A detailed review of published results does not permit a decisive opinion on the subject as most of the results are based on punctual and limited observations. The interest in hybridization is not restricted to hybrid vigor but also includes combination and transfer of favorable characteristics. Several larch improvement strategies based on inter- and intra- specific hybridization are discussed. Reciprocal recurrent selection seems particularly attractive. Nevertheless, none of the present strategies, including the F, generation as a breeding population, can be excluded. Precise knowledge on genetic properties of traits selected for are required before any firm recommendation can be made. There is an urgent need for well designed, long-term experiments set up on several sites to obtain more insight into these delicate questions. Use of a two-level factorial mating design is recommen- ded, in particular to avoid some of the approximations made in past experiments. Moreover, valuable information on genetic parameters, e.g. combining ability, heterosis, will be gained at both intra- and inter-species and intra- and inter-population levels and may help tree breeders in their choice of a more efficient hybridization strategy for the improvement of larch. larch - hybridization - improvement strategies - heterosis Résumé &horbar; Hybridation des mélèzes : revue critique et incidence pour l’amélioration. L a supériorité du mélèze hybride (Larix X eurolepis Henry) sur ses espèces parentes (Larix decidua Mill. et Larix kaempferi (Lamb.) Carr.) a été reconnue et décrite par de nombreux auteurs. Elle ne se limite pas à la croissance mais concerne aussi divers caractères économiques importants. Une confusion existe cependant dans la littérature entre trois notions : hybridation, supériorité de l’hybride et hétérosis. En particulier, cette supériorité du mélèze a été assimilée dans de nombreux cas à un effet d’hétérosis. Une revue minutieuse de la littérature ne permet pas cependant dans l’état actuel de nos connaissances de confirmer ou d’infirmer ce rapprochement car les résultats publiés résultent souvent d’observations ponctuelles et partielles. Il est rappelé que l’intérêt de l’hybridation ne se limite pas à la seule vigueur hybride. Diverses stratégies d’amélioration des mélèzes par hybridation inter-spécifique (et intra-spécifique) sont briè-
vement discutées. La sélection récurrente de nombreux avantages. Cepen- réciproque présente voie, y compris celle utilisant la génération F dant population d’amélioration ne I aucune comme peut être a priori rejetée tant qu’une connaissance précise des pro,oriétés génétiques du matériel étudié (en particulier, le rapport dominanceladditivité) n’est acquise sur les caractères concernés par l’amélioration. En vue de répondre aux diverses questions posées, la mise en place de dispositifs expérimen- taux rigoureux, multisites et conçus pour des observations à long terme apparaît comme une prio- rité. Afin d’éviter certains écueils d’expériences antérieures (choix du matériel parental de référen- ce), le recours à un plan de croisement factoriel à 2 niveaux est recommandé. Des informations précieuses sur les paramètres génétiques (capacités à la combinaison, hétérosis, etc.) pourront être obtenues aux niveaux intra- et inter-spécifiques et intra- et inter-populations et devraient per- mettre d’orienter le travail des améliorateurs. mélèze - hybridation - stratégies d’amélioration - hétérosis received Introduction sis, it has subsequently been with by European countries. some reserve results have been published Contradictory The transfer of European larch (Larix its heterotic response. on decidua Mill.) seed sources from their nati- This paper will first discuss the results ve range (the Alps) to more lowland areas published on hybrid larch with special has not been successful in France. Sev- reference to hybrid vigor, and then will eral provenance tests have shown its poor consider possible alternative hybridization adaptation, slow growth, and canker sus- strategies which could benefit from the ceptibility (Lacaze and Birot, 1974; Fer- heterotic response. rand and Bastien, 1985, Schober, 1985) when cultivated at lower elevations. On the other hand, Japanese larch Larix kaempferi (Lamb.) Carr., an exotic species Hybrid larch and hybrid vigour from Hondo Island, Japan, initially ap- peared to be a promising successor to European larch with fast juvenile growth on larch has mainly Hybridization work and canker resistance. However, its requi- been concerned with inter-specific crosses; only minimal interest has been rement for moisture during the vegetative shown in intra-specific crosses. Various period restricts it to more limited oceanic sites. Even so, the Larix genus remains possible crosses between species of the Larix genus have been reported through- very attractive for its silvicultural advan- out the world, but the most economically tages, namely light-tolerant species, no ones currently concern hybrids plantation problems, fast juvenile growth, important between European larch and Japanese relatively short rotation, and the high quali- ty of its timber. larch, and between the Japanese larch and the Korean larch (Larix gmelinii A hybrid between the European and Rupr.). In Europe, only the former is culti- Japanese larch (Larix X eurolepis Henry) vated and will be discussed. first described in 1919 by Henry and Flood Hybrid larch has been extensively plan- (1919) opened new perspectives for larch ted in regions such as Scotland (> 55,000 tree improvement programes. The hybrid ha. by 1980) (Destremau, 1987) and Den- was advocated for its outstanding growth mark, but at present it is nearly absent in performance, usually described as hetero-
rial to which they are compared. These French forests for various reasons, the include either provenances (natural or arti- cause being the lack of reforesta- principal tion material. ficial) or families. The results are normally positive, though highly variable, irrespecti- Inter-specific hybridization of larch has of the various ages of the tested mate- ve long been cited for its positive heterotic rial and contrasting regions in Europe that effect, a property it shares with other they originate from. When Hybrid larch forest trees such as poplars, eucalyptus height growth is generally found to be and pines. The superiority of hybrid larch much more significant vis-a-vis European as regards morphological and phenologi- larch than vis-a-vis Japanese larch. cal characteristics, growth traits, wood properties and physiological parameters hybrid larch other than Positive traits in has been illustrated (Matyssek, 1986). In also outlined in Table II. growth are addition, it seems to be much more resis- Results are presented as the relative ran- tant to larch canker (Lachnellula willkom- king of the hybrid when compared to the mii (Hartig) Dennis) (Keiding, 1980) than parental species. The hybrid generally many of the European larch populations. ranks higher for several important charac- TableI presents some of the most teristics such as stem form and wood significant results presented in the literatu- mechanical properties. However, the re on hybrid larch growth performance hybrid ranks only intermediate for several wood physical properties. Wood volume involving various types of hybrid progenies shrinkage and heterogeneity in particular (control or open pollinated families), as well as diverse sources of parental mate- could well be negative aspects of hybrid Table1. Superioritv (expressed in %) of hybrid larch parental species for total height. over
parents (Falconer, 1960) is (Bastien and Keller, 1980). Some often larch more contradictory results (e.g., for stem form, redefined by tree breeders as its superiori- its best parent. Moreover, while branching habit, wood density) also exist ty over breeders take pure inbred lines as between experiments. These will be dis- crop cussed later. their reference point, forest tree breeders work if not at the species level, actually larch’sreciprocal, Larix X lep- Hybrid then at least at the population level or at toeuropea Dengler, has not received the best with individuals which are presum- same amount of attention, although the ably highly heterozygous. Dunkeld hybrid from which all the hybridi- zation work on larch originates was produ- Two criticisms may be levelled at these ced from this formula. In a German experi- different concepts. First, by only com- ment, (Gothe, 1987), at 33 years this paring hybrids to the best parent, it is clear hybrid showed a slight advantage in that several hybrid families will be neglec- height growth but a slight loss in diameter ted and only part of the potential gain growth compared to its reciprocal Larix X connected with heterosis will be obtained eurolepis. Results from other published (Schmitt, 1973). Second, study at the spe- studies do not permit a conclusion to be cies or population level might be sufficient made regarding the superiority of one over to show advantages of hybridization, but is the other. Nevertheless, the success of of little use for advanced selection and the hybrid X eurolepis seems more due to above all for interpretation of heterosis. favorable conditions of artificial pollination As mentioned previously, results pre- than to its real superiority over its recip- sented in Talbles I and II show some rocal. inconsistency in the observed level of &dquo;heterosis&dquo; for height growth-rate; in addi- Heterosis or hybrid vigor, commonly defined as the superiority of the hybrid tion there are some contradictory results over the mean performance of both for various traits.
Apart from the restrictions of some of (1980) support this view that the and Reck the experimental designs from which growth superiority of the hybrid is at its these results were obtained, it should be greatest during the first 10 yr. This opinion stressed that the parental material with is also upheld by Scamoni (1977) but data which the hybrid progenies are compared collected from a French experiment (Fer- is, in several cases, represented by prove- rand and Bastien, 1985) is not in agree- nances to which the parents of the hybrid ment with these results. At age 26, the do not even belong or by full-sib families hybrids retained not only their absolute but with which the hybrid families share no also their relative superiority in volume common parent. This raises the question production over the parental species. of the choice of the reference parental There is at present no clear answer to material, which in many cases can only be the question of a durable superiority over considered to be the best material avail- time of the hybrid over its parents. This able and not necessarily adapted to the uncertainty, however, points to urgent specific test sites. need for proper experimental designs for In comments made by Schmitt addition, long-term observations. Nevertheless, cited by Reck (1977) concern the (1973) without taking into consideration other hybrids themselves. He points out that possible advantages of the hybrid, it due to the difficulties of control pollination, seems clear that a faster initial growth rate hybrid heterosis has very often been de- with a consequently shorter rotation and a scribed on an individual basis rather than hypothetical final higher total wood pro- for a population of individuals, so that duction should be sufficient to justify a general conclusions on heterosis of larch hybridization program for larch. can hardly be drawn. Another question for which no relevant The majority of the results given in information has been presented so far Table II concern young material, with the concerns heterotic stability over a range of oldest data available from plantations of environments. Most of the results presen- mid-rotation age. The question should be ted in TablesI and 11 are from experiments raised as to whether this early superiority on one site only. It would be necessary to of hybrid material continues and therefore test for genotype X environment interac- constitutes true heterosis, or whether it is tion to define conditions in which hybrid just a temporary faster initial phase of superiority occurs and to interpret its growth. An illustration of the latter situation causes (combination of characteristics, was given by Namkoong (1963) for a hybrid habitat). Several examples in the hybrid between Loblolly and Longleaf forestry literature illustrate this problem. pines. The answer to this question has not Hyun’s results on poplar hybridization been clearly determined but is of prime (Hyun, 1974) show that the hybrids tested importance in tree breeding. show heterosis only in certain specific Analysis of periodic growth increments environmental conditions. Inter-provenance by Gothe et al. (1980) and Gothe made hybridization work with Norway spruce in (1987) in a German experiment indicated Sweden also indicated that the hybrid that from an age of 20 yr, the hybrid (between Central European and Swedish = shows a slight reduction in its absolute populations) was superior in growth to production advantage, but a strong reduc- both parents only at the latitudes of the tion in its relative production advantage northern parent. This was attributed to the over the progenies of the pure parent spe- combination of better growth ability of the cies. Results presented by Keiding (1980) southern parent with the frost hardiness of
the northern parent (Nilsson, 1974). Simi- ted although F seedlings are widely used 2 lar behavior could also be observed in in Scotland. Difficulties encountered in the larch hybrids including Larix siberica (Nils- production of F, generation reproductive son, 1959). On the other hand, several material on a commercial scale necessi- studies can be cited in which no relation- tate this option. Rohmeder and Schonba- ship between heterosis and environmental ch (1959) found &dquo;that F and backcross 2 quality could be found (Owino and Zobel, hybrids of Japanese X European larch 1977; Roman-Amat, 1984). grew vigorously but did not possess the same degree of hybrid vigor as F hybrids&dquo; 1 As suggested by Keiding (1962), part of (cited from Wright, 1976). Other examples the superiority of hybrid larch could be have been given by Vincent and Fer explained by its greater drought resistance (1965) and Lacaze and Birot (1974). and in general by its higher degree of &dquo;fit- Although they compare F, and F proge- 2 ness&dquo;. Its advantage over the parental nies derived in a different fashion, it is species would therefore &dquo;show up more interesting to note that F progenies still 2 clearly under more adverse conditions in show superiority over the pure parental respect of climate and site&dquo;. Experiments species but to a lesser degree than the F 1 on a range of sites currently being under- progenies and show a comparable variabi- taken in France by INRA will hopefully lity. answer some of the questions. The continuing superiority of hybrids The greater uniformity of the F genera- 1 due to &dquo;heterosis&dquo; over several genera- tion progeny over the parental progenies tions has received little attention in forest- has also been recognized as an advan- ry. Depending on which factors deter- tage in favor of hybrids. This was the main mined heterosis, reduction in hybrid vigor conclusion drawn by Lacaze and Birot (if the cause was dominance or overdomi- (1974) where the F, hybrid larch progeny nance) or continuation of vigor (combina- tested was characterized by a remarkable tions of genes with additive effects, hybrid homogeneity for most of the traits studied. habitat) in the F and following genera- 2 Similar conclusions were drawn by Fer- tions can be expected (Wright, 1976). rand (1986) for height measured at the Epistasis might, however, modify the nursery stage, but more recent observa- reduction in vigor. A greater variability in tions on the same hybrid families indicate the F compared to the F, material can be 2 that this conclusion should be modified expected. However, in a study with Pinus with respect to hybrid formula and charac- rigida X taeda, Hyun (1976) noted no teristics. Reck (1977) found a similar situa- significantly different performance in the tion amongst both the most homogeneous F compared to the F generation and no 2 1 and the most heterogeneous families. significant increase in variability. Similar Selection and breeding for uniformity of observations have been reported by growth do not have the same degree of Nikles (1981) for other species. The result importance as in crop breeding, since thin- led Hyun (1976) to recommend use of F 2 ning is a common practice in commercial generation material (wind pollinated prog- forestry. Nevertheless, breeding for unifor- eny from F plantations) for commercial 1 mity could be of importance in areas with plantations of this pine hybrid in lowland a low stocking intensity type of forestry. regions of South Korea. For other economic traits such as wood quality, homogeneity would constitute a The of F generation material of growth 2 larch has not been well documen- definite improvement. hybrid
larch and Hybrid laricina for its hybridization pro- presumably good adaptation to wet soils (Ferrand, 1986). grams Interest in lies in 3 main hybridization first, heterosis for a given char- Tree improvement programs for larch areas : acteristic; second, combination of traits benefit from several characteristics inher- leading, for example, to better adaptation ent in the Larix genus. Among those which (e.g., growth and drought resistance), are of special interest to the tree breeder including those traits which might be nega- are its great potential for inter-species tively associated through linkage or pleio- crossability (no major barriers), its relative- tropy; and lastly, transfer of a favorable ly precocious (10 yr) ability to produce characteristic, (e.g., pest resistance) from abundant flowering, its monoecious char- one population to another, where it might acter, its suitability for vegetative propaga- have been lacking. A higher degree of fit- tion, and the ease of its establishment in ness of the hybrids and uniformity can plantations. also be considered important properties Growth traits, stem and crown habits (Keiding, 1962). (basal sweep, stem straightness, branch- ing habits), wood quality, and pest resis- Most of the work larch inter-specific on tance (e.g., larch canker) are the main hybridization presented in the literature selection criteria. Wide soil adaptability describes heterotic success obtained from and growth uniformity are also of impor- mainly random crossing of individuals, and tance. its early evaluation through sexual or vegetative propagation. A short-term A great deal of genetic variability exists breeding strategy using early tests might for these traits in larch. Recent results give rapid and substantial gains (Table II, from 2 international European larch prove- with the previously-noted reservations). In nance experiments (Lacaze and Birot, this way, INRA is testing in France some 1974; Schober, 1985, 1987) have stressed 600 hybrid families over a range of poten- the importance of the choice of seed origin tial sites for larch. Preliminary results indi- for reforestation. Amongst the most promi- cate that there are several families with sing for cultivation at low elevations are juvenile growth rates comparable to other origins from the Sudetan mountains (280- vigorous species such as Douglas fir and 620 m), Central Poland (150-650 m), and an apparent wide soil adaptability. some northeastern Austrian alpine origins. The first two are favored for their growth Rational use of the parental populations capacity and canker resistance, while the and their evaluation through hybridization third shows excellent stem form. as described above will depend on basic Japanese larch also shows variability knowledge of gene action for the but particular recommendation as characteristics used in selection. Manage- no regards origin has been made. Fast juve- ment of the F, hybrid generation as a nile growth and high resistance to larch breeding population and its possibly suc- canker are two of its most valuable char- cessful exploitation through F generation 2 acteristics. Experiments with other larch also depends on these genetic properties. species have usually been limited in Systematic studies of general and specific combining abilities of the genetic material Europe to arboreta. Potential advantages for the main traits of interest, through well through hybridization could be obtained designed multisite experiments will be from crosses with Larix sibirica for cold resistance (Nilsson, 1959) and with Larix necessary to determine the relative pro-
portion of dominance to additivity of the which are canker-susceptible, would be traits, their level of inheritance and corre- recommended. lations, and their stability over time and According ta the mode of gene action, space. alternative strategies have been proposed for the development of hybridization pro- There would appear to be no such stud- grams, and in particular to take advantage ies for larch. It is, however, currently assu- of heterosis (Namkoong, 1979; Falconer, med but without any rigorous proof that 1981When much of the genetic variance &dquo;heterosis&dquo; for growth traits is unpredic- is additive for the traits selected, classical table unless specific crosses are made, recurrent selection should be most effi- suggesting they would depend on non- cient. Selectioin could occur either in the additive gene action (Keiding, 1980; Reck, parental popul;ations prior hybridization, to 1977; Vincent and Machanicek, 1972). used in this for trait combinations or Nilsson’s conclusions (1959) suggest, case transfer, or after hybridization in the F 1 however, that the action may be predomi- generation or most likely a combination of nantly additive. Stem form, on the other both levels. When non-additive gene hand, would depend on additive effect action effects prevails, inbreeding- according to Keiding (1980). No informa- outcrossing methods could be more effi- tion is available for other traits. cient than selection methods without A strategy using complete or partial fac- inbreeding. torial designs with or without reciprocal Investigations on inbreeding!utcros- crosses would be recommended. The size sing possibilities in larch hybridization of the breeding populations (hundreds of have been conducted in Denmark by Kei- trees) and their structure (as mentioned ding (1968). His results, based on a limi- above, at least 3 European larch popula- ted number of crossings between two non- tions are of interest to us) as well as tech- inbred European larch parents and a few nical constraints connected with artificial number of first-generation selfed (S1) control pollination (e.g., irregularity of flow- parents of Japanese larch, show that non- flower damage by frost, non- ering, negligible supplementary gains (5-10%) matched flowering times, pollen conserva- and uniformity for total height can be tion, low full seed set per cone) will obtained in this manner compared to nor- definitely restrict the mating design to a mal (no selfing) inter-specific crossing. manageable number of parents. A two- However, this approach requires extensive level diallel (Hinkelmann, 1974) or better and systematic: progeny testing. suited to our purposes, a nested popula- tion diallel or factorial mating design such However, inbreeding of larch through as that used by Park and Gerhold (1986) self-pollination is usually expressed by in a Scotch pine inter-population hybridi- deleterious effects such as reduc- severe zation study seem promising. These desi- tion of full seed set, low seed germination, gns could give valuable preliminary infor- high mortality, reduced vigor, crooked mation on combining abilities and growth, lack of apical dominance and heterosis at both family and population reduced fertility (Dieckert, 1964) though some progenies show remarkable unifor- levels. Moreover, some important trends mity and contain some fast-growing trees. intra-specific hybridization potential on could also be obtained. A restricted selec- Development of the technique requires tion of widely contrasting parents (e.g., 5) continuous inbreeding over several gener- ations to increase genetic divergence be- per population, so as to avoid any a priori elimination of individuals, except those tween parental populations. Selfing up to
is to be the third generation (S3) has proved to be parental species populations achieved. possible with Douglas fir (Orr-Ewing, 1976); but this is a rather unique example An important gain in time is obtained, - in forestry. Its feasibility with larch beyond since before release of selected hybrid the second generation of selfing is not material is made, an extra-generation for known far. so selfing is not required as for the inbreed- The Recurrent Selection Reciprocal ing-outcrossing strategy. has been little used in (RRS) strategy However, irrespective of the strategy forest tree breeding but was recommen- selected, biological constraints such as ded by Conkle (1970) and Hyun (1976) for the large number of crosses which must pine hybridization. Its efficiency for tree be made and tested and unpredictable breeding is not known, but promising flowering mean that improvement cycles results with maize have been obtained will be long (as with many other forest tree (Moll and Stuber, 1971; Eberhart, 1977). improvement programs). Early flower The RRS strategy combines several induction and development of reliable advantages which might be compatible juvenile tests especially for early detec- - with a general larch improvement pro- tion of heterosis could be very reward- - gram, as long as heterosis exists and is ing in shortening intervals. generation connected with non-additive gene effects. The advantages are the following : Development of crosses with high - Hybrid larch and its commercial utiliza- specific combining abilities; at each gener- tion ation, high performance specific crosses can be selected and regenerated for com- mercial forest application. F progenies 1 Selected hybrids can- be prepared for com- may be conserved for a further possible mercial utilization through mass prop- exploitation in F generation. 2 agation by either sexual or vegetative Parental species populations are methods. To take maximum advantage of - maintained separately and are simulta- . non-additive effects, bi-clonal orchards neously genetically improved. This aspect using parents which show a high degree is particularly important, as individual spe- of specific combining ability should be cies and the hybrid have their own inter- used. Direct vegetative multiplication of est, and separate individual programs specific crosses themselves can be used might not be developed because of limited as an alternative, especially when there is budgets and facilities. Intra-species selec- a shortage of seed. tion performed in this manner might not be Both methods are feasible and have as efficient as classical recurrent selection already been adopted by several breeding in each species, as illustrated by Moll and programs. Yet, to use them efficiently and Stuber {1971 ) with maize. to determine their place in breeding strate- Inbreeding deleterious effects due to gies first requires clear responses to seve- - selfing are avoided. ral important questions. The objective of this chapter is not to make a complete of intra-species Inbreeding depression - review of the literature on these two topics population crosses does not reduce gain as much of the work, especially on vegeta- in the hybrid product (Namkoong, 1979) tive propagation, is not published and is control of inbreeding level is though evolving rapidly, but to give an overview of recommended if continuous progress in
general question that the tree breeders around these problems as long as this faced with. solution meets selection objectives. are Vegetative propagation Sexual mass propagation Vegetative propagation by means of root- Bi- or pauci-clonal orchards have been ing cuttings has been attempted in several planted in most European countries with countries with variable results depending varying success (Keiding, 1970, Steinmetz on clone identity, age and treatment of the et al., 1987; Nanson, personal communi- stock plants and cultivation conditions cation). Failures are mainly attributed to (John, 1979; Mason, 1984; Cornu and frost damage of strobili (Ferrand, 1988), to Nanson, personal communication). Multi- irregular flowering, and most of all to plication of young seedlings from selected general non-overlapping phenology be- hybrid famines (bulk propagation) or of tween European and Japanese larch single individuals selected at a later stage (Mitchell, 1958) resulting in a low propor- are presented as alternative solutions tion of true hybrid seed. Low number of full (Bonnet-Masimbert et al., 1987). No seed per cone is also a major handicap. recommendation can be made as long as Poor results have been recorded in Fran- precise and concordant indications on with a hybridization orchard, which has ce genetic (i.e., feasibility of very early selec- been successful in Denmark. Separation of tion of heterolic families, level of intra- the two parent clones in different orchards, family genetic variability, minimum require- mechanical pollen collection in one and ment of genetic diversity in forest mass-supplemental pollination in the other, plantations), physiological (i.e., influence is a solution that is currently being tested in of physiological age on rootability and cut- France (Steinmetz et al., 1987). Selection ting growth habit, rejuvenation opportuni- of parents with matching phenology could ties), technical, and economic (e.g., be another solution in the absence of any acceptable multiplication rates, size of clo- bad correlations with economic traits, and nal park) parameters are not known. in particular with heterosis. With the hypothesis that the hybrid X eurolepis and its reciprocal X leptoeuro- Conclusions pea are equivalent in terms of general per- fomance, one question remains on the respective role of both parental species as A hybridization strategy based on selec- genitors in the orchard. male female No or ting outstanding crosses showing up in general answer can be formulated. A pre- random matings amongst individuals cise knowledge of the individual clones might be suitable for short-term hybridiza- phenology and their ability to produce tion programs whose main objective is a male and female gametes is required as quick release of hybrid material for refor- well as their level of autosterility. A better estation. Such programs are under way in understanding of the incompatibility bar- many European countries for inter-specific riers resulting in the observed low rate of hybridization of larch. full seed is also needed. programs will Long-term improvement Use of F generation material from better management of genetic require 2 a selected F, generation hybrid plantations resources including breeding within pure would be an economical way of getting species populations. Several hybridization
P. (1987) Research on hybrid vigour and its use exist. It is not breeding strategies possible in the genus Larix : preliminary studies and to recommend any single strategy since methodological aspects. Proc. Eur. Seminar, there is still a lack of basic genetic infor- Wood Production and Harvesting, Bologna, mation. Initially studies of hybrid behavior Italy, June 1987, pp. 5 in long-term, multisite, well designed expe- Conkle M.T. (1970) Hybridization. Application to riments with appropriate parental refer- pine populations. Proc. IUFRO, Raleigh, NC, ences should be established. These would August 1969, Sect. 22, 131-133 investigate the role of heterosis in actual Deret E. & Keller R. (1979) Etude Compar6e hybrid growth superiority, conditions of its du Bois de M616ze d’Europe (Larix decidua manifestation, and its stability over sites Mill.), de M616ze du Japon (Larix leptolepis and time. Choice of an adequate mating Gord.) et de leur Hybride (Larix X eurolepis design (for example a nested population Henry). CNRF Stat. Rech. sur la Qualité des factorial) should give precise indications Bois, Doc. 3, pp. 20 on inheritance patterns. Destremau D.X. (1987) Un Gisement de Bois Inter-specific hybridization of larch might inattendu : I’Ecosse. Afocel-Armef, Informa- be interesting even in the absence of tions-Foret No. 2, pp. 105-120 heterosis but this consideration does not Dieckert H. (1964) Einige Untersuchungen zur preclude preliminary research on genetic Selbsterilitat und Inzucht bei Fichte und Larche. parameters. Silvae Genet. 13 (3), 77-86 options available number of There are a (1977) Quantitative genetics and Eberhart S.A. for the propagation of selected mass breeding. Proc. Int. Conf. Quanti- practical corn hybrids, and given the present state of our tative Genetics, Iowa State Univ., Ames, Iowa, knowledge none, even use of F genera- 2 pp. 491-502 tion material, can be rejected. Falconer D.S. (1960) Introduction to Quantitati- ve Genetics. Longman, 2nd edn, pp. 340 In many cases, economic considera- tions will be a limiting factor and any prog- Ferrand J.C. (1986) Melezes. Rev. For. Fr. (n° ress in reducing the generation interval spécial) 38, 142-145 through early flower stimulation and Ferrand J.C. (1988) Electric heating units in pol- development of juvenile tests for heterotic iination bags avoid damage to flowers by spring with quick vegetative coupled response frost. Ann. Sci. For. 45 (2}, 157-160 should be given the highest propagation Ferrand J.C. & Bastien J.C. (1985) Bilan à 26 priority. ans d’une plantation comparative de m6l6zes. Rev. For. Fr. 37 (6), 441-448 Gothe H. (1987) Ein Kreuzungsversuch mit Larix europaea D.C., Herkunft Schlitz, und References Larix leptolepis Gord. Alig. Forstztg. 158 (1 }, 1-3 Gothe H., Schober R. & Bork H. (1980) Ein Bastien J.C. & Keller R. (1980) lnt6r6ts compa- Kreuzungsversuch mit Larix europaea D.C., r6s du m6l6ze hybride (Larix X eurolepis Henry) Herkunft Schlitz, und Larix leptolepis Gord. avec les deux espèces parentes. Rev. For. Fr. 2 Allg. Forstztg. 151 (6-7), 101-112 32 (6), 521-530 A. & Flood M.G. (1919) The history of the Henry Bellon S. (1967) Winiki Badan nad wzrostem Dunkeld Larch. Proc. R. Irish Acad., Sec. B. 35 mieszanca modrzewia Larix eurolepis Henry w Hinkelmann K. (1974) Two-level diallel cross Lasach doswiadcza lnych sggw w rogowie. experiments. Silvae Genet. 23 (1-3), 18-22 FoGa For. Pol. Ser. Aesn. Zeszyt 13, 127-155 Hyun S.K. (1974) The expression of heterosis Bonnet-Masimbert M., Cornu D., Ferrand J.C., of improved hybrid poplars in Korea being Mellerowicz E., Said C., Villar M. & Zandonella
influenced by the site and the cultural method. Namkoong G. (1963) Comparative analyses of Proc. Joint IUFRO Meeting, S.02.04.1-3, Stock- introgression in two pine species. Ph.D. thesis, holm, Session III, pp. 167-196 School of Forestry, NCSU, Raleigh, NC Namkoong G. (1979) Introduction to Quantita- S.K. (1976) Interspecific hybridization in Hyun tive Genetics in Forestry. USDA Forest Service, with the special reference to pinus rigida pines Tech. Bull. No. 1 !¡88, pp. 342 X taeda. Silvae Genet. 25 (5-6), 188-191 Nanson A. & Sar.re E. (1978) A propos de I’h6- John A. (1979) Propagation of hybrid larch by t6rosis de Larix :< eurolepis, en particulier pour and winter cuttings. Silvae Genet. 28 summer les propri6t6s du bois. Bull. Rech. Agron. Gem- 220-225 (5-6), bloux 13 (4), 323-336 H. (1962) Krydsningsfrodigned hos Keiding Nikles D.G. (1981) Some successful hybrid laerk. Dansk. Skovforen. Tidsskr. 47, 139-157 breeds of forest trees and need for further Keiding H. (1968) Preliminary investigations of development in Australia. Proc. 7th Meeting inbreeding and outcrossing in larch. Silvae RWG, No. 1, Forest Genetics, Trafalgar, Victo- Genet. 17 (5-6), 157-200 ria H. (1970) Evaluation of seed orchards Keiding Nilsson B. (1959) Om LArkfr6 och ldrkhybrider established for the production of hybrid larch, for mellansverige. Sven. Skogsvardsfdren. Ti d- Larix eurolepis Henry. For. Tree Improv. 1, 1-24 skr. 57 (2), 309-324 Keiding H. (1980) Hybridlaerkens vaekst og til- Nilsson B. (1974.) Heterosis in an intraspecific pasningsevne i forhold til de rene arter. Dansk. hybridization experiment in Norway spruce Skovforen. Tidsskr. 65, 204-234 (Picea abies). Proc. Joint IUFRO Meeting, S. 02.04 1-3, Stockholm, Session III, pp. 197-205 Kiellander C.L. (1974) Some examples of hybrid vigour in Larix. Proc. Joint IUFRO Meet- Orr-Ewing A.L. (!! 976) Inbreeding Douglas fir to ing, S.02.04.1-3, Stockholm, Session III, pp. the S generation. Silvae Genet. 25 (5-6), 179- 3 207-2133 183 Lacaze J.F. & Lemoine M. (1965) Comporte- Owino F. & Zobel B. (1977) X Envi- Genotype ment de diverses provenances de m6l6zes en genotype stability in ronnement interaction and Bretagne. Ann. Sci. For. 22 (2), 321-351 Loblolly pine. Silvae Genet. 26 (2-3), 114-116 6 Lacaze J.F. & Birot Y. (1974) Bilan d’une exp6- Park Y.S. & Gerhold H.D. (1986) Population rience comparative de provenances de m6l6zes hybridization in Scotch pine (Pinus sylvestris à I’Age de 13 ans. Ann. Sci. For. 31 (3), 135- L.). I. Genetic variance components and hetero- 159 sis. Silvae Genet. 35 (4), 159-201 Mason W.L. (1984) Vegetative Propagation of Reck S. (1977) E:rgebnisse einer Versuchsanla- Conifers Using Stem Cuttings. II. Hybrid Larch. ge mit europaischen Larchen (Larix decidua Forestry Commission, Research Information Mill.) und Hybridtarchen (Larix eurolepis Henry). Note 91/84/SILN, pp. 3 Silvae Genet. 26 (2-3), 95-101 R. (1986) Carbon, water and nitrogen Matyssek Reck S. (1980) Untersuchung über das Holz relations in evergreen and deciduous conifers. der Hybridldrche. Alig. Forstztg. 151 (6-7), 117- Tree Physiol. 2 (1-3), 177-187 120 Mitchell A.F. (1958) Establishment of a seed Rohmeder E. & Schonbach H. (1959) Genetik orchard for the production of hybrid larch seed. Parey, Berlin und Zuchtung der Waldbaume. Forestry Commission, Rep. for year ending Roman-Amat B. (1984) Contribution à [’explora- March 1958, pp. 138-147 tion et a la valorisation de la variabiiite intraspé- Moll R.H. & Stuber C.W. (1971 ) Comparisons of cifique et individuelle du pin Laricio de Corse, response to alternative selection procedures ini- Pinus nigra Arn., ssp. Laricio var. corsicana Loud. These de Docteur lng6nieur, Univ. Paris- tiated with two populations of maize (Zea mays L.). Crop. Sci. 11, 706-711 Sud, pp. 144
Scamoni A. (1977) Uber Larchenhybriden aus Vincent G. & Fer F.(1965) Krizenci modrinu freier Bestaubung und über die weitere Ent- japonskeho na pokusn6 plose evropsk6ho a Lesniho zavodu Litovel. Lesn. Cas. 4, 367-378 wicklung gelenkter Larchenkreuzungen. Beitr. Forstwirtsch. 11 (1), 21-26 Machanicek J. (1972) Heterozni Vincent G. & krizenc u. Lesnictvi, (Prague) modrinovych rust Steinmetz G., Baldet P. & Rousselet M. (1987) (6), 523-536 Production de Graines Hybrides de M616ze : R6colte M6canis6e du Pollen. CEMAGREF, Wright J.W. (1976) Introduction Forest to Informations Techniques, cah. 68 (4), pp. 1-7 Genetics. Academic Press, pp. 463