Báo cáo khoa học: "The article in possible status of wood quality oak breeding programs (Quercus petraea Liebl and Quercus robur L)"

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article Original possible status of wood quality The oak breeding programs (Quercus petraea Liebl in and Quercus robur L) G Nepveu INRA, Station de Recherches sur la Qualité des Bois, Champenoux 54280 Seichamps, France Summary — The first part of the paper presents experimental results illustrating the very high level of phenotypic variability of the anatomical and physical characteristics of the wood (Quercus petraea and Quercus robur) (density, shrinkage, color, etc) and technological properties, namely suitability for slicing. Then some studies are reviewed, which show that a large part of the phenotypic variabil- ity in the wood of oak is likely to be under genetic control (individual level). In the second part of the paper, 3 kinds of studies which are still needed for optimum selection of wood quality are proposed: 1) defining realistic selection criteria for wood quality; 2) confirming genetic control of wood quality criteria; and 3) defining conditions for performing optimum selection for wood quality. This last point is treated in the context of possible developments in oak silviculture and regeneration. Quercus / wood / quality / breeding / selection Résumé — Place possible de la qualité du bois dans les programmes d’amélioration généti- que des chênes (Quercus petraea Liebl et Quercus robur L). Dans une première partie, l’auteur présente des résultats expérimentaux témoignant d’une variabilité phénotypique très forte pour les caractéristiques anatomiques, physiques (densité, retrait, couleur du bois, etc) et technologiques, notamment l’aptitude au tranchage, des bois de chênes rouvre et pédonculé. Il poursuit en faisant état des résultats de quelques études qui montrent qu’une partie importante de la variabilité phéno- typique serait sous contrôle génétique (variabilité génétique intraprovenance). Dans une seconde partie, les études préalables à la prise en compte de la qualité en matière de sélection des chênes sont évoquées : 1) définition de critères réalistes de sélection pour la qualité; 2) confirmation de la réalité du contrôle génétique sur les critères de qualité et 3) définition des conditions de réalisation de la sélection. Ce dernier point est traité en tenant compte des évolutions possibles de la sylvicul- ture appliquée aux chênes. Quercus / bois / qualité / amélioration génétique / sélection
INTRODUCTION WHY TAKE WOOD QUALITY INTO ACCOUNT IN AN OAK BREEDING PROGRAM? The aim of this paper is to examine the im- portance of wood quality in an oak breed- ing program. Two questions arise: why take wood quality into account? How can it High level of phenotypic variability be taken into account? for basic and technological properties in wood of oak Only Quercus petraea Liebl and Quercus robur L are considered here. In France, these are the only oaks of economic interest. All studies devoted to oak have shown that First of all, it seems to be useful to define the phenotypic variability of the wood prop- realistic criteria for the wood quality of oak. erties of Q petraea and Q robur is very Furniture and joinery are uses of primary high. TableI gives some examples of such interest for oak. The decreasing availability variability observed on some wood ana- of high-grade tropical timbers will empha- tomical characteristics, basic and techno- size the economic significance of oak for logical properties. such uses. For these purposes, the follow- In oak, high levels of phenotypic vari- ing characteristics are necessary (Nepveu, ability have also been detected for spiral 1990), in addition to suitably shaped logs: grain (Birot et al, 1980) and sensitivity to 1) low wood shrinkage; 2) no internal frost cracks (Miller, 1987). cracks, namely frost shakes; 3) straight If the priority of wood quality for some grain; 4) suitable color and other esthetic traits (especially regularity of radial forest species is sometimes discussed, growth); and 5) small amount of sapwood. these data clearly show that in oak, wood
properties cannot be neglected because First experimental results they are too important for the use in joinery about genetic control and furniture making. Because of the small number of experi- In addition, only part of the large pheno- mental plots available, there is little infor- typic variability of oak wood properties is mation about the genetic control of wood explained by ring width. This means that properties in oak. In spite of this, results trees of good quality and relatively high obtained by Nepveu (1982, 1984a, b) and rates of radial growth can be found. In Kanowski et al (1990) on juvenile to very many cases, between-tree variabilities are juvenile clonal or progeny material clearly given for mixed Q robur and Q petraea demonstrate that individual genetic (geno- trees. However, it should be noted that the typic) control is: 1) very strong for individu- amount of phenotypic variability remains al vessel area in the earlywood (h 0.6- 2 = in each species. high very 0.9); 2) strong for basic density (h 0.3- 2 = 0.6); 3) interesting for wood shrinkage and earlywood width (h 0.3-0.4); and 4) low 2 = Presumption and first experimental but significant for vessel percentage in the results about genetic control earlywood, latewood width and fiber per- of wood quality in oak cent in latewood (h 0.1-0.25). These re- 2 = sults were obtained for Q robur and Q pe- traea separately. about genetic control Presumption Nepveu’s results (1984a) the rela- For Presumptions about the genetic control of tively low heritabilities observed for some wood quality are based on 3 facts: 1) in anatomical traits are explained by low ac- other tree species, the genetic control of curary of image analysis results at that most wood properties is high at the indi- time. vidual tree level (Nepveu, 1986); 2) in oak, between-tree variability for wood properties appears to be high even if HOW SHOULD WOOD QUALITY BE these trees are even-aged, have the TAKEN INTO ACCOUNT IN A POSSIBLE same ring widths, have grown in the same OAK BREEDING PROGRAM? stand. So, between-tree variability cannot be explained by silviculture and environ- As described below, taking wood quality ment but only by microsite and/or genetic into account in an oak breeding program differences; and 3) in oak, even if be- has 3 requirements. tween-tree variability is high, many wood properties do not vary significantly within the tree (when ring width and age from Define realistic criteria the pith are fixed). As mentioned above, for selection of wood quality this fact has to be related to microsite and genetic effects. However, taking into ac- count the rotation length in oak silvicul- Selection for quality against, for example, ture, it is doubtful that microsite differenc- shrinkage, frost cracks, spiral grain, for es- es could explain the observation that the thetic appeal and a high proportion of cambium of a 200-year-old tree has pro- heartwood cannot be realistically per- duced earlywood vessels of the same di- formed directly: easily measurable criteria ameter during most of its life! have to be found for this purpose.
Selection against percent sapwood Selection against shrinkage and spiral grain The first results gained by Eyono Owoundi Possibilities other than direct selection are (1991) show that wood density combined difficult to imagine for these 2 important with ring width and age from the pith are characteristics. Spiral grain is known to be good predictors of wood shrinkage: if both genetically controlled but patterns of within- of the other two characteristics are main- variability are confused and seem to be tree tained constant, shrinkage increases when closely dependent upon individual trees. wood density and ring width increase and For these 2 characteristics, phenotypic age from the pith decreases. and within-tree variabilities will have to be Additional information on shrinkage ob- studied intensively before any decisions tained by measurements of wood anatomy about selection strategies can be made. are expensive to carry out and yield little a possible consequence of In addition, further information. the percentage of sapwood decreasing has to be evaluated in terms of tree physi- ology, namely the role of sapwood thick- Selection against sensitivity ness and water content during drought. to frost cracks Some basic properties and anatomical General comments characteristics of the wood have been realistic criteria for identified as having value in identifying In attempting to identify wood quality, one im- selection based frost-cracked trees (Savill, 1986; Cinotti, on be stressed: recent pre- portant point 1991) namely: individual vessel area in the can liminary results (Eyono Owoundi, 1991; earlywood, wood density, wood ray num- Huber, 1991 b) appear to show that wood ber, wood shrinkage, spiral grain and stem density versus ring width curves in oak water content. could provide synthetic information about research is needed to At present, more wood properties and anatomy. In addition, identify realistic and certain selection crite- parameters of such curves depend upon ria for sensitivity to frost cracks. individual trees and seem to be under ge- netic control, as shown in figures 1 and 2. It can be noted too that: figure 1 con- Selection for wood esthetics firms the previous intuition and results of Polge and Keller (1973), who found that for Because of its high variability and, as a the same ring width, 2 oak trees can exhib- consequence, large variability in prices of it very large differences in wood density; the final products, esthetics cannot be ne- figure 2 indicates that clones with low den- glected in selection. However, in spite of sity (and probably as a ’statistical’ conse- initial work in this field performed on oak quence, low shrinkage) can be found in veneers (Mazet and Janin, 1990), end- spite of wide ring widths. This type of tree, user’s needs still have to be identified if not susceptible to frost cracks and es- clearly in terms of wood structure and thetically acceptable, could be valuable for properties. farm forestry and to complete the natural regeneration in ’classical’ silviculture. Such studies will probably have to in- hope that quantitative and qualitative measure- The results show that clude we can ring width for giving density wood extractives. ments versus curves on
the chosen breeding program (see below); individual trees might provide information and 4) special attention has to be given to other wood properties and anatomy, on juvenile-mature genetic correlations. and on the genetic value of the tree. If veri- fied, their use for effective and realistic se- lection, even on phenotypes in the forest, Define conditions of performance could be valuable. in selection for wood quality Such selection could be non-destructive in accordance with developments using X-ray scanning of increment cores. in oak silviculture and regeneration Estimate or confirm the level of genetic Two conditions should be considered: 1) control on wood criteria identified continuation of ’classical’ silviculture based as realistic predictors of wood quality on natural regeneration, in which case, genetic improvement would consist of cutting down trees which are not desirable following points are considered impor- The as parents; and 2) development of artificial 1) Q robur and Q petraea must be tant: regeneration in existing stands or planta- considered separately; 2) genetic gain for tions of new ones (farm forestry, etc) in wood quality has to be sought at the indi- which case, genetic improvement could be vidual tree level (ie genetic or genotypic use progenies ’classical’, ie, namely level within the provenance); 3) estimation more testing and multiplication. and clone of genetic parameters must be adapted to
In either case, the time between gener- Early results have been encouraging. grams. ations will be high. Therefore, research will However, significant work remains, have to be focused on methods of selec- mainly in: 1) defining realistic criteria for tion which provide rapid genetic gain for wood selection: this point certainly repre- wood quality. In this event, estimation of sents the major part of the work; 2) con- the genetic value of mature parent trees firming the level of genetic control on (for sexual or vegetative reproduction) above-mentioned criteria; and 3) devising through minute evaluation of their pheno- strategy(ies) for wood selection which are type will be a crucial operation. effective and adapted to oak silviculture. CONCLUSION ACKNOWLEDGMENTS Much in wood be improvement quality can expected if wood properties are taken into A substantial part of the results mentioned here consideration in possible oak breeding pro- have been made possible thanks to the financial
Marchal R (1983) Intérêt de la prise en compte MA 1B/ support of the EEC DE XII Programme de caractéristiques physiques et anato- 0009-0016, 0037-0038 ’Genetics and Breeding miques simples du bois de chêne pour of Oaks’. l’appréciation de la qualité des placages d’ébénisterie. DEA thesis, Université de Nan- cy, 105 p REFERENCES Mazet JF, Janin G (1990) La qualité de l’aspect des placages de chênes: mesures de couleur Birot Y, Dufour J, Ferrandes P, Teissier du Cros et critères d’appréciation des professionnels E, Az&oelig;uf P, Hoslin R (1980) Variabilité de français et italiens. Ann Sci For 47, 255-268 l’angle du fil du bois chez quelques feuillus: Miller P (1987) La gélivure des chênes pédoncu- hêtre, chêne et Eucalyptus dalrympleana. lé et sessile dans le centre de la France. As- Ann Sci For 37, 19-36 pects descriptif, stationnel, technologique et (1991) Recherche de propriétés in- Cinotti B sylvicole. 3rd year thesis, ENITEF, 70 p trinsèques du bois pouvant expliquer la sen- G (1982) Variabilité clonale de Nepveu sibilité à la gélivure de Quercus petraea l’infradensité chez Quercus petraea. Pre- (Liebl) et Q robur (L). Ann Sci For 48, 453- miers résultats obtenus sur boutures d’un an. 468 Ann Sci For 39, 151-164 Eyono Owoundi R (1991) Modélisation de la ré- G (1984a) Déterminisme génotypique Nepveu tractibilité du bois par la largeur de cerne, de la structure anatomique du bois chez l’âge médullaire et la densité du bois des Quercus robur. Silvae Genet 33, 91-95 chênes indigènes (Quercus robur L et Quer- cus petraea Liebl). Appendix to the final re- la Nepveu G (1984b) Contrôle héréditaire de port for EC contract: Genetics and Breeding densité et de la rétractabilité du bois de trois of Oaks. Station de Recherches sur la Qua- espèces de chênes (Quercus petraea, Quer- lité des Bois, CRF, INRA Nancy, 23 p cus robur et Quercus rubra). Silvae Genet Flot JL (1988) La couleur du chêne de tranch- 33, 110-115 age français. Méthodologie de la mesure, va- Nepveu G (1986) Faut-il se préoccuper des pro- riabilité géographique, classement industriel priétés du bois dans le cadre des pro- et incidences économiques. 3rd year thesis, grammes d’amélioration génétique des ar- ENITEF, Station de Recherches sur la Qual- bres forestiers ? Rev For Fr 38 (special ité des Bois, CRF, INRA Nancy issue) 221-227 (1991a) Variabilité et liaisons phénoty- Huber F Nepveu G (1990) Les facteurs influençant la piques juvénile-adulte pour la structure anat- qualité du bois de chêne (chêne rouvre, omique du bois des chênes indigènes (Quer- chêne pédonculé). Rev For Fr42, 128-133 cus robur L et Quercus petraea Liebl) Nepveu G, Huber F (1991) Variabilité inter- et in- Appendix to the final report on EC contract: tra-arbre du nombre de rayons ligneux chez Genetics and Breeding of Oaks, Station de les chênes indigènes (Quercus robur L et Recherches sur la Qualité des Bois, CRF, Procédure Quercus Liebl). petraea INRA Nancy, 89 p d’échantillonnage. Appendix to the final re- Huber F (1991b) Modélisation de l’infradensité port on EC contract: Genetics and Breeding du bois en fonction de la largeur de cerne et of Oaks, Station de Recherches sur la Qua- de l’âge médullaire chez les chênes in- lité des Bois, CRF, INRA Nancy, 14 p digènes (Quercus robur L et Quercus pe- Polge H, Keller R (1973) Qualité du bois et lar- traea Liebl). Appendix to the final report on geur d’accroissement en forêt de Tronçais. EC contract: Genetics and Breeding of Oaks, Ann Sci For 30, 91-126 Station de Recherches sur la Qualité des Bois, CRF, INRA, Nancy, 21 p Savill PS (1986) Anatomical characters in the wood of oak (Quercus robur L and Q petraea Kanowski PJ, Mather RA, Savill PS (1990) Ge- Liebl) which predispose trees to shake. Com- netic control of oak shake: some preliminary monw For Rev 65, 109-116 results. Silvae Genet 40, 166-168