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Session1 – Overview of poplar breeding programs in Europe

Breeding and selection of poplar in Netherlands Sven M.G. de Vries Alterra, Wageningen University and Research Centre, PO BOX 47, 6700 AA Wageningen, The Netherlands mailto:[email protected]

Poplars are common in The Netherlands, both in roadside plantations and in forestation. The resent past production of poplar wood of approx. 245,000 m3 was derived from an area of approx. 16,000 ha poplar forest and approx. 15,000 ha of roadside- and borderline plantations. Before World War II selection within existing Poplar material was commonly used in The Netherlands. Since 1948 breeding was added. Collections throughout the entire distribution ranges of P. nigra, P. deltoides and P. trichocarpa took place. New variability was created through controlled crossings. All together a total of about 500,000 seedlings were produced from which about 10,000 survived selection criteria concerning healthiness and growth. Many comparative trials all over the country were established with these 10,000 clones and many of those showed their significance for practical use through the years. The main part of the work has been the hybridizing by controlled crosses of pure species, primarily female P. deltoides with male P. nigra and/or male P. trichocarpa. Occasionally other poplar species like P. maximowiczii or hybrids were used. In a later stage also back crosses and triple crosses were carried out. The main traits that decided about the continuation with every of the individual seedlings were the tolerance for leaf diseases as poplar rust (Melampsora larici-populina) and Marssonina brunnea. Seedlings that passed both these criteria and grew satisfactory were cloned and evaluated in a test for bacterial canker (Xanthomonas populi). Clones that successfully passed the canker test were grown in comparative trials for final evaluations on growth, form, and branch behaviour and wind tolerance. After about 15 to 20 years some of these clones that proved to be really good in all aspects were released to practice, but only after a final test in trials with bigger blocks per clone. For commercial reasons and because some of these clones also proved to be good to very good in other European countries they have been released all over Europe including the protection of European breeders rights. The latest application for European breeder’s rights on four new clones dates from 2006. This concerns four Euramerican clones (P. deltoides x P. nigra in different combinations) named: ‘POLARGO’, ‘ALBELO’, DEGROSSO’ and ‘SANOSOL’. The previous clone ‘KOSTER’ that was introduced to Europe from the Dutch breeding program dated from 1989 and is still a great success in many European countries.

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Session1 – Overview of poplar breeding programs in Europe

Poplar Breeding Programme in Flanders, Belgium Bart De Cuyper INBO, Research Institute for Nature and Forest, Gaverstraat 4, 9500 Geraardsbergen, Belgium mailto: [email protected]

From an economical point of view, poplar is by far the most important hardwood tree species in Flanders, covering about 21,750 ha (i.e. 13.8 % of the forest area) and accounting for 50 % of the hardwood timber production. Afforestation with poplar amounts to 300 ha per year, leading to a permanent demand for high quality reproductive material. The poplar breeding programme, which was started in 1948, aims at meeting this demand through the production and commercialization of poplar clones with high growth potential, disease resistance, superior wood quality and high rooting capacity. The essence of the breeding strategy is the performance, on a yearly basis, of controlled crossings, initially between three species, viz P. nigra, P. deltoides and P. trichocarpa. In 1960, P. maximowiczii was introduced in the breeding programme. Non-recurrent F1 breeding, intrainterspecific breeding and backcross breeding were adopted as main breeding systems, applying single-pair mating and nested mating design simultaneously. Genitors for controlled crossings are selected within a large basic collection, mainly constituted by genotypes selected within the full-sib progeny of crossings, completed by vegetative material of genotypes selected within the natural distribution area, genotypes selected within the half-sib progeny of the existing basic collection and through international exchange programmes of seeds and pollen. Selection is based on the principle of independent culling levels, focusing on disease resistance, rooting capacity, adaptation to climate, soil and photoperiod, vigour, form and wood quality as main selection criteria. Since the mid-nineties, the poplar breeding programme was increasingly supported by biotechnological research. Between 1972 and 1995 the breeding programme resulted in the selection and commercialization of 15 cultivars. Selection for complete resistance to Melampsora larici-populina caused the breakdown in the 80’s and 90’s of rust resistance due to emergence of new pathotypes This major setback led to a radical change in the former selection strategy aiming at complete rust resistance: inter- and intraspecific crossings were performed with genitors marked by a durable, partial resistance and tolerance to rust. Major outcome was the selection and commercialization in 1999 and 2005 of six cultivars displaying tolerance towards rust. Recent research aspires to assess the potential of a “non-classical” polyclonal poplar culture, characterized by the use of selected seedlings, planted at short distances and subject to a traditional type of forest management of successive thinnings.

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Session1 – Overview of poplar breeding programs in Europe

Poplar Breeding in Germany : State of art and future perspectives Dr. Karl Gebhardt1 and FD Dr. Heino Wolf2 1

Northwest German Research Station, Department of Forest Genetic Resources, Prof. Oelkers-Str. 6, D-34346 Hann.Muenden 2 Staatsbetrieb Sachsenforst , Abt. Ressourcenmanagement, Referat Forstgenetik/Forstpflanzenzüchtung, Bonnewitzer Str.34, D-01796 Pirna mailto: [email protected]

mailto: [email protected]

Beside the utilization of woody biomass for pulp and paper, particle boards and combustion new technologies create an increasing demand of wood. The biomass to liquid technologies led to the establishment of new industries. The pellet production for automatic combustion increased exponentially with in the last five years. There is also a technology which allows the formation of tubes (dimensions above 50 cm) from solid wood without loss of material. Effective production systems in short rotation can be established with certain poplar cultivars but the Act on forest reproductive material allows only to use material of the category tested. Examples are given for the approval of newly tested aspen cultivars. The reproductive material must be true to type and the cultivars must be kept separate during the course of propagation. It should become a common sense to apply DNA techniques in order to identify clones and to proof their trueness to type. Breeding objectives and selection criteria are related to the wood products and perspective rotation periods. The knowledge of the inheritance of phenotypic growth characters would allow more effective selection and the shortening of breeding cycles. The current situation at the market of forest reproductive material in Germany is described. Many recommended clones are available only in small quantities. The increase of propagation capacities takes time and possibly only less favourable material becomes available. The suitability of tested material from other European countries is mostly not known and not tested under German site conditions. A proposed German research program entitled “FastWood” is described.

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Session1 – Overview of poplar breeding programs in Europe

Poplar Breeding Activities at GIS « Peuplier » in France: A. Berthelot, Pdt of GIS Peuplier, FCBA- Charrey sur Saöne C. Bastien, B. Thoirain, M. Ménard, P. Poursat,, INRA (Orléans, Nancy, Angers) P.Baldet, V. Bourlon, CEMAGREF Nogent sur Vernisson O.Forestier, Pépinière forestière de l’Etat de Guéméné-Penfao mailto: [email protected]

In France, poplar area (constituted mostly by cultivated plantations) amounts to about 250,000 hectares. Poplar plantations with rotations about 15-20 years and low density of plantation are found in four main regions of production: Aquitaine-Midi-Pyrénées, Pays de Loire-Charente, Bourgogne and Picardie-Nord. Pedoclimatic conditions and severity of pests and insects attacks vary significantly between the different regions. Despite increasing promotion of poplar as a bioenergy crop with high potential, no more than 200 ha of Short Rotation Coppice plantations have been inventoried. During the last five years, average annual wood production was1.5 million cubic meters. The less favourable poplar market of the last few years explains a significant reduction of establishment of new plantations (number of poplar plants sold in 2007: 830,000). Since 2001, FCBA (ex-AFOCEL), CEMAGREF and INRA are joining their efforts of research and development under a collaborative structure called GIS “Genetics, Breeding and protection of poplar”. They are assisted by the national forest nursery of Guéméné-Penfao. GIS “Peuplier” programme has two main objectives: (1) the evaluation of performances of new cultivars created in France and in foreign countries to deploy the best adapted material to French conditions, (2) management of short and long term breeding programmes for different uses of poplar in France. Short term activities are developed according three directions: (1) Selection of best clones from intraspecific controlled crosses done by INRA and AFOCEL during the eighties, (2) Selection of P. ×canadensis clones using the best P. deltoides and P. nigra parents available in breeding populations with as main objective to diversify genetic diversity used in both parental species and to identify clones with high plasticity and high productivity level even in northern part of France, (3) Selection of P. ×interamericana clones with high tolerance to pests and disease, especially to Melampsora laricipopulina. Selection is done according to a multistage procedure on rooting ability, growth rate, resistances to Melampsora spp, branchiness, Marssonnina brunnea, Xanthomonas populi, stem form and wood properties. In order to get precise estimation of genetic values, evaluation of performances combine clonal nursery tests at high density, laboratory tests for rust resistances, specific field tests for rust tolerance, resistances to Marssonnina and bacterial canker and multisite field plantations with single tree plot or multiple tree plots. Current status of selection process for P. x canadensis and P.x interamericana are presented. Long term activities are focusing on control of genetic diversity in parental breeding populations and possibility of prediction of favourable allelic combinations in both intra and inter-specific hybrids. Important investments were done in clonal evaluation of large breeding populations of the three species (P. deltoides, P. trichocarpa and P.nigra). More over, neutral diversity of these populations is under evaluation with microsatellites markers (and in the near future with SNP markers) and will participate in breeding population sub-structuring. Intra-specific crossings followed by individual selection have been carried out in the three parental gene pools in order to create elite parental populations. Three limiting factors of selection efficiency have been identified: (1) duration of the selection cycle which needs more efficient tools especially during the first stages of selection, (2) limitation in field evaluation when plasticity over sites and years is more and more required, (3) possibility of developing durable resistances to pest and diseases in clonal cultivation with exotic genetic resources.

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Poplar Breeding at CRA-PLF in Italy Lorenzo Vietto CRA-PLF, Consiglio per la ricerca e sperimentazione in agricoltura, Unità di ricerca per le produzioni legnose fuori foresta, Casale Monferrato, Italy mailto: [email protected]

The poplar plantations area in Italy amounts to 118,533 hectares, 70,000 of which are situated in the Northern plains (2005, last update). The total area has remained rather stable since the early nineties. In 2006 poplar wood production was 0.86 million cubic metres (70 % related to the clone ‘I-214’), that is nearly 50% of total domestic wood production. Particularly in the Po river plain, poplar cultivation is going through an economic and technical crisis as regards management planning and methods of cultivation. The main cause is an unfavourable poplar market which as settled at a very low level. Establishing low density plantations (270-280 plants per hectare instead of 300-330), with relatively short rotations (about 9 to 13 years) is the trend to obtain trunks of higher quality and greater flexibility in the cultivation cycle. To minimize the risks of the singlecrop system and to obtain high quality wood, plantations where poplar was mixed with noble broadleaves and shrubby species (cycle of cultivation 20 years) were successfully tested in Lombardy. In this Region, where biomass thermoelectric power plants are under construction and the Program for Rural Development included a series of financial incentives to support the establishment and maintenance of SRF plantations, about 6,000 hectares of SRF have been planted over the last 5 years. Since 1999, new poplar clones which have been positively evaluated by the Technical Committee of the National Poplar Commission on the basis of preliminary experimental trials can be provisionally registered in the National Register of Basic Forest Material; breeders can commercialise clones in an advanced phase of selection which have demonstrated to be productive and resistant to diseases. A Legislative Decree (n. 386/2003) that includes the Directive 1999/105/CE on the marketing of FRM has been approved by the Italian Government. Regions are at present the official Control Board of the marketing and quality of FRM. Since 2005 to date 17 new poplar clones have been registered in the category “monitored” in the National Register of basic Forest Material for wood production and other 2 new clones have been provisionally registered (category “qualified”) for short rotation coppice; 6 new clones have been submitted to the National Poplar Commission by the Alasia Franco Vivai Company (other 8 clones, submitted in 2002 by the CRA-PLF, are still under examination). At the CRA-PLF the poplar breeding program set up in the early eighties is running. A systematic breeding approach where long-term and short-term breeding are integrated is considered. In long term breeding the aim is to maintain genetic variation to create options for the future, whereas in the short term the effort is to reach economic goals (production and selection of new hybrids for intensive poplar cultivation and short rotation coppice). The program is based on a semi-reciprocal recurrent selection of P. deltoides and P. nigra. The aim is to produce improved populations of both species and to obtain parents of high breeding value to produce valuable P. xcanadensis hybrids. Inter-specific crossings have been carried out in the first stage of the program using poly-cross and common tester methods to evaluate P. deltoides females and P. nigra males respectively (incompatibility between P. deltoides males and P. nigra females); a breeding program using F1 P. ×canadensis clones selected within the population originated from the progeny test is going on; parents are grouped in subpopulations according to their characteristics of resistance to Melampsora, Marssonina, Venturia, Phloeomyzus passerinii, Discosporium populeum. The best individuals (8 clones) have been submitted to the National Poplar Commission. Intra-specific crossings have been carried out in the second stage of the program; a pool of intra-specific hybrids is at present in an advanced stage of selection. A second cycle of intra-specific crossings among the selected parents within the original P. deltoides and P. nigra populations is planned for the coming years. Growth rate and rooting ability will be considered for the first species; growth rate, branchiness, resistance to Marssonnina brunnea and Melampsora spp. for the second one. TREEBREEDEX Activity n°5

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A breeding program for commercial purposes started at the beginning of the 1990’s using the best P. deltoides and P. nigra parents selected on the basis of progeny tests and combining ability; at present, 34 P. ×canadensis clones are in an advanced stage of selection. The use of biotechnology and DNA markers to speed up selection and breeding programs is considered too. Protocols for the genetic transformation of poplar clones (P. ×canadensis, P. deltoides, P. nigra , P. alba) have been set up to obtain transgenic plants with enhanced and durable resistance to insect pest and to confer tolerance or resistance to non selective herbicides. As regards the application of molecular markers, a high number of micro satellites have been evaluated on plant material from the on-going breeding program. Highly polymorphic, consistent and co-dominant markers, such as micro satellites or simple sequence repeats (SSR), provided excellent markers for clone and cultivar identification in poplars. Molecular markers will be employed for mapping and characterizing natural genetic resources. Marker assistance selection (MAS) for useful agronomics traits (i.e. abiotic and biotic genetic resistance) and quantitative characters will be applied in conventional breeding programs in order to reduce selection time and optimize work. The weak point of population breeding is the long time required for the selection cycles and the main problem will always be the allocation of limited resources. Moreover the advanced techniques that should support population breeding compete for research funds. The flexibility of a multiple-population breeding strategy, an effort to create cooperative breeding programs within and across national boundaries and a cooperation with growers’ organizations for the clonal selection could be the answer for a sustainable poplar breeding effort.

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Session1 – Overview of poplar breeding programs in Europe

Parental line improvement and breeding of elite poplar in a short rotation tree improvement program in Italy Maurizio Sabatti1 and Fabrizio Nardin2 1

DISAFRI, Università della Tuscia - Via San C. de Lellis snc, 01100 Viterbo, Italy Alasia Franco Vivai, Str. Solerette 5/a, 12038 Savigliano (Cuneo), Italy mailto: [email protected] mailto: [email protected] 2

Producing green energy through the use of woody biomass from short rotation coppice (SRC) gives to farmers an interesting alternative to traditional crops reducing reliance on fossil fuels. In addition, woody biomass can be used as raw material for the manufacture of various bio-based products like bioethanol. The cultivation of hybrid poplars for woody biomass in SRC (2 to 5 years) combine the use of very productive poplar clones and appropriate agricultural practices giving high yields. Italy, with an area of more than 6,000 hectares, is actually the European country with the widest land area planted with poplar in SRC. In the last years emphasis has been placed by Alasia Franco Vivai, in collaboration with DISAFRI-University of Tuscia and IBAF-CNR, in the selection and evaluation of fast growing poplars. In parallel, new equipments have been developed for planting, cultivating and harvesting operations in SRC applying novel specific agricultural techniques. The breeding program for the selection of fast growing poplars is composed of intra-specific breeding for parental line improvement and inter-specific breeding for F1 hybrid generation. Germplasm collections of P. alba (in cooperation with DISAFRIUniversity of Tuscia), P. nigra, P. deltoides, P. trichocarpa and P. maximowiczii have been established in the last 20 years. Parental line improvement starts with the evaluation of growth and susceptibility to rust of half sib progenies for two years and about 5% of the seedlings are selected for placement in a breeding archive. Some of these selections will flower at age 4-5, allowing additional intraspecific crosses to be made primarily within P. deltoides and P. nigra according to an assortative mating scheme. Production of elite F1 hybrid begins with inter-specific crosses following an incomplete factorial mating design. Hybrid progenies are evaluated at the end of the first year for growth and rust attack and about 70% of the seedlings are selected and tested in the nursery for two years. The top 10% clones are selected for placement in a clonal archive. Ten replicates per genotype of the selected hybrid poplars at this stage are further evaluated for 2 years in the nursery for rooting, form, sensitivity to pest and insect and growth. Only the top 1-2% poplar passing this stage are presented to the field evaluation prescribed by the National Poplar Council authorizing the commercial deployment of the poplar clones.

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Experiencies of Hungarian Forest Research Institute in the field of poplar breeding Attila Borovics FRI, Forest Research Institute, Department of Breeding, H-9600 Sarvar, Varkerulet 30/A, Hungary mailto: [email protected]

Today 56% of the Hungarian forest area is covered by indigenous tree species. The rest (44%) is occupied either by introduced and domesticated species (such as black locust, red oak and conifers) or by improved poplars. Poplar forests comprise 10% of the total forest area of Hungary (7% improved poplar, 3% native poplar), approximately 190,000 hectares. The most popular varieties have been produced through the artificial crossing of Populus deltoides (American eastern cottonwood) and Populus nigra (Eurasian black poplar) (Populus × euramericana) in Hungary. As a result of international relations almost 800 poplar clones have been introduced into Hungary. Only 14 clones of these have been registered, because a special site situation of Hungary. This assortment has been expanded, as a result of Hungarian poplar breeding activity over the last years, by 4 registered varieties and 5 candidate varieties. Domestic varieties (Pannonia♀, Koltay♂, Kopecky ♂) have some major advantages in Hungarian ecological condition: • • •

frost resistance tolerance of sites resistance to diseases and pests.

Together with the varieties already registered and brought into cultivation a number of promising domestic clones are waiting for registration. It is mainly these promising clones which are tested in the clonal and variety selection tests carried out on nearly 230 hectares managed by Forest Research Institute. The tests are meant to study the performance of the clones, their pest resistance and site requirements.

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Hybrid aspen and Poplar breeding in Sweden Lars-Göran Stener Skogforsk, the Forest Research Institute of Sweden, Ekebo 2250, 26890 Svalöv, Sweden mailto: [email protected]

Aiming to produce superior hybrid aspen commercial material, a breeding project was initiated at Skogforsk in 1985. A total of 280 plus trees of hybrid aspen, Populus tremula. x P. tremuloides, were phenotypically selected from trials and stands at 20 to 40 years of age. All clones were vegetatively propagated and planted on 14 test sites in southern Sweden during the period 1986-1991. Genetic results from these clonal tests, each including 40 to 100 clones, replicated 8-20 times in randomised block design using single tree plots, showed 1) a great genetic variation for growth and stem quality traits 2) high broad-sense heritability, 3) weak genotype x environment interactions and 4) strong age x age correlations for growth traits. Overall, the results after 8-12 years of growth in field demonstrated possibilities of powerful clone selection after early evaluation of clone tests at just one or a few sites. The 15 genetically best out of the totally 280 tested clones have been selected for commercial use in southern Sweden. Other poplar species such as P. balsamifera, P. nigra, P. trichocarpa and P. deltoides and hybrids between some of them are also tested at three sites including totally 140 clones. All clones have been received from other breeding organisations in Europe, since Sweden does not have any domestic poplars. The tests were established in year 1991 and evaluated after approx. 10 years of growth. There was a high clonal variation for growth and stem quality traits. Climatic adaptation seems to be a major problem. For instance, trees with high biomass production during the first 10 years can suddenly die. The 15 best clones have been selected for commercial use in southern Sweden on sites not exposed to frost.

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Populus breeding strategies in Lithuania Rita Verbylaité, A. Pliüra, A. Gradeckas, S. Kuusiené LFRI, Lithuanian Forest Research Institute, mailto: [email protected]

The only naturally occurring Populus species in Lithuania is Populus tremula; therefore almost all research concerning this genus is made on European Aspen. Populus tremula research in Lithuania started in the middle of the last century. The work was carried out by Dr. R. Murkaitė. She was interested in phenology, phenotypical forms, pollination, vegetative and generative propagation of European Aspen. As well she made some test crosses between Populus tremula and two other species of this genus (e.g. P. alba, P. tremuloides). Dr. R. Murkaitė was followed by A. Pliūra, who made second series of crosses between above mentioned species. He extended number of trees involved and extracted some genetic parameters. Later on, Populus tremula haven’t gained much attention and interest. It was considered as „rubbish species“. In recent years this opinion changed and at the moment we are starting new projects on European aspen. Lithuanian Forest Research Institute Molecular genetics and biotechnology lab is creating methodologies for mass multiplication of selected best clones of hybrid aspen, which originates from early test crosses. As well we are interested in genetic diversity of naturally growing Populus tremula. For this purpose we have used RAPD to investigate genetic diversity of Lithuanian Populus tremula. As well we are trying to identify the least susceptible trees to Ph. tremulae, which is known as the major pathogen that causes stem rot in this species. Future plans. At the moment we are selecting best phenotypes in progeny test plantations of aspen hybrids, planning to propagate them by in vitro tissue culture. Afterwards we are planning to establish clonal trials and test best trees for short rotation plantations.

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Populus breeding program in Slovakia Roman Longauer NLC, TG Masaryka 22SK 960-92 SVOLEN, Slovakia mailto: [email protected]

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Towards durable tolerance of poplar to pest and insects in poplar cultivation Marijke Steenackers INBO, Research Institute for Nature and Forest, Gaverstraat 4, 9500 Geraardsbergen, Belgium mailto: [email protected]

Poplar plantations began to cover Europe already at the beginning of the 20th century. Massive deployment of Populus nigra L. and some euramerican hybrids in south-central Europe heralded a new area of intensive poplar culture all over Europe. In order to increase yield and wood quality, poplar breeding programs were initiated in several European countries during the 40’s and 50’s, mainly producing vigorous F1 hybrids between P.deltoides and P.nigra, P.deltoides and P.trichocarpa or P.tremula x P.tremuloides. However, unceasing progress in terms of both quantity and quality was very soon accompanied by an exponential increase in the toll exacted by pests and insects. Due to introduction of exotic pathogens the situation was even growing worse. As in crop and animal breeding, poplar breeders very soon acknowledged the need for disease and insect resistance as one of the most important selection criteria. For some diseases, e.g. bacterial canker (Xanthomonas populi) and Marssonina brunnea blight, breeders were successful in selecting disease-tolerant varieties. For others such as Melampsora rust, a selection strategy for complete resistance was adopted. However, it soon became clear that selection for complete resistance was not the strategy to be followed. The attempt to completely control the pathogen obviously led to the emergence of more virulent pathotypes. Nowadays, the challenge of poplar breeders is to manage their breeding populations in a way that increases the frequency of interesting alleles for resistance. Introduction from new genepools is also a major concern of this strategy. An essential component of poplar breeding is the need for research on both the genetic variability of the pathogen and the available genetic variation within the host. The development of artificial infection methods to evaluate tree resistance towards the most harmful pests and insects will speed up the selection process. Besides resistance, tolerance (i.e. the ability of the host to maintain growth despite susceptibility to the pathogen) should be introduced as an important selection criterion in the breeding process. Further research is needed in order to identify phenological and physiological characteristics which are genetically related to tolerance and which therefore can be used as additional selection criteria.

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Diversity of traits associated with biomass production, water-use efficiency and water-stress tolerance in the Populus genus. Nicolas Marron1,2,3, SY. Dillen2, R. Monclus1,4,C. Bastien4, R. Ceulemans2, E. Dreyer3, M.Villar4 and F. Brignolas1 1

LBLGC, Laboratoire de Biologie des Ligneux et des Grandes Cultures, Université d’Orléans, 45067 Orléans, France Research Group of Plant and Vegetation Ecology – University of Antwerp – B-2610 Wilrijk, Belgium3 INRA-Université-EEF, UMR 1137 Écologie et Écophysiologie Forestières, 54280 Champenoux, France 4 INRA-UAGPF, UR588 Amélioration, Génétique et Physiologie Forestières, BP 20619,45166 Olivet cedex, France mailto: [email protected] 2 3

The increasing importance of bioenergy due to the present geopolitical and environmental context has promoted a renewal of interest for tree cultivation under short rotation regimes in Europe. For biomass production purposes, poplar has been shown to be particularly well adapted. The development of poplar cultivation in the context of climate changes has generated new requirements concerning the characteristics of the genotypes to be planted: trees need to be able to tolerate abiotic constraints (drought, high temperatures); they should combine a satisfactory biomass production and an optimum water-use efficiency. However, (i) the links between these three properties, (ii) their response to varying growth conditions, and (iii) their relationships with architectural (branchiness), phenological (bud set and bud burst) and leaf (growth, physiology and structure) traits, known as important growth determinants, are highly variable and would need to be organized into a hierarchy. As an illustration, five experiments* are presented. They all aimed at the same general objectives: (1) to assess the amplitude of the diversity available within the Populus genus in terms of productivity and water-use efficiency (WUE, as assessed from 13C isotope discrimination in leaves) and (2) to estimate the relevance of using leaf growth, physiological and structural traits as indicators of these two complex traits, i.e. productivity and WUE. All five experiments were composed of P. deltoides x P. nigra hybrids, but differed in terms of growth conditions, as well as age and nature of the plant material. The links between the traits and their range of variation were highly dependent on the growth conditions. However, some of the observed relationships among traits were valid irrespective of the conditions. The major result was that the tested cultivars display a large diversity in 13C discrimination which is at least partly due to a diversity in WUE, and that WUE was independent of the productivity of the cultivar. This opens an avenue for selection provided a few preliminary requirements are fulfilled. *Corresponding references: 1. Marron N., S.Y. Dillen and R. Ceulemans. 2007. Leaf determinants of productivity in poplar depend on environmental conditions and genetic background. Environmental and Experimental Botany. 61: 103-116. 2. Marron N. and R. Ceulemans. 2006. Genetic variation of leaf traits related to productivity in a Populus deltoides x P. nigra family. Canadian Journal of Forest Research. 36: 390-400. 3. Monclus R., E. Dreyer, M. Villar, F.M. Delmotte, D. Delay, J.-M. Petit, C. Barbaroux, D. LeThiec, C. Bréchet and F. Brignolas. 2006. Impact of drought on productivity and water use efficiency in 29 genotypes of Populus deltoides x Populus nigra. New Phytologist. 169: 765-777. 4. Monclus R., E. Dreyer, F.M. Delmotte, M. Villar, D. Delay, E. Boudouresque, J.-M. Petit, N. Marron, C. Bréchet and F. Brignolas. 2005. Productivity, leaf traits and carbon isotope discrimination in 29 Populus deltoides x P. nigra clones. New Phytologist. 167: 53-62. 5. Marron N., M. Villar, E. Dreyer, D. Delay, É. Boudouresque, J.-M. Petit, F.M. Delmotte, J.-M. Guehl and F. Brignolas. 2005. Diversity of leaf traits related to productivity in 31 Populus deltoides x P. nigra clones. Tree Physiology, 25: 425-435.

TREEBREEDEX Activity n°5

INRA-Orléans, 18-19 Sept 2008

Session 2 – Breeding Challenges for the next decades

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INRA-Orléans, 18-19 Sept 2008

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Session2 – Breeding challenges for the next decades

Poplar Breeding Strategies : How to improve them ? Catherine Bastien INRA-UAGPF, UR588 Amélioration, Génétique et Physiologie Forestières, BP 20619,45166 Olivet cedex, France mailto: [email protected]

Poplar breeding programs around the world have achieved substantial increases in growth and yield potential through careful combination of intra/interspecific hybridization and clonal selection. Major challenges of future poplar breeding include (1) continuous genetic gains for recognized economic traits while addressing new breeding goals, (2) optimization of large-scale deployment of the selected genetic variation to limit economical and environmental risks associated to clonal forestry, (3) bringing genomic technologies to application in conventional poplar breeding. Breeding strategies for poplar breeding programmes will be analysed in the light of significant developments done in different national and European research plans during the past ten years. Knowledge acquired in the following areas will be presented for discussion: (1) Intra/interspecific hybridization: performances and heterosis level in different hybrid combinations including Populus deltoides, P. trichocarpa and P. nigra; respective levels of among- and within-family variations for a suite of traits of interest; relationships between intra and interspecific combining abilities, relationships between clonal value and combining abilities. (2) Juvenile-Mature correlations, optimal selection ages for different selection objectives (3) GxE interaction, phenotypic plasticity for different traits of interest (growth, phenology, disease resistance, branching habit, water use efficiency, wood properties) (4) Optimal management of genetic diversity in breeding populations (5) Development of marker/gene-based selection: where do we stand? How could we progress? The breeder’s efforts will not stop at designing genetically improved trees, but need to define rational deployment strategies that do not neglect the potential impacts that improved material may have on the environment and for end-users in the context of climate change and diversification of poplar cultivation schemes.

TREEBREEDEX Activity n°5

INRA-Orléans, 18-19 Sept 2008

Session 2 – Breeding Challenges for the next decades

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INRA-Orléans, 18-19 Sept 2008

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Session2 – Breeding challenges for the next decades

Breeding for added values of poplar wood products Dries VanSteenkiste Laboratory of Wood Technology, Faculty of Bioscience Engineering (FBE), University of Ghent, Coupure Links 653, 9000 Gent, Belgium. mailto: [email protected]

TREEBREEDEX Activity n°5

INRA-Orléans, 18-19 Sept 2008

Session 2 – Breeding Challenges for the next decades

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INRA-Orléans, 18-19 Sept 2008