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Breeding of fast growing forest tree species for biomass production in Greece
b i o m a s s a n d b i o e n e r g y 3 4 ( 2 0 1 0 ) 1 5 3 1 e1 5 3 7
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Review
Breeding of fast growing forest tree species for biomass production in Greece F.A. Aravanopoulos* Laboratory of Forest Genetics & Tree Breeding, Faculty of Forestry and Natural Environment, PO Box 238, Aristotle University of Thessaloniki, 54124 Thessaloniki, Greece
article info
abstract
Article history:
The purpose of this review is to provide a critical analysis of the literature regarding the
Received 13 July 2009
breeding of fast growing forest tree species dedicated to biomass production in Greece and
Received in revised form
to identify future goals. The main genera employed in pertinent research which show the
30 April 2010
most promising results for operational plantations belong to Populus spp. and Platanus spp.
Accepted 17 June 2010
The best poplar clone (P. x euramericana I-455) produced 16.54 t ha1 y1 dry weight averaged over different experimental plantations and rotation periods, while the best clone derived from the Greek breeding program (Populus deltoides var. missouriensis Populus nigra
Keywords:
var. pubescens He-X/3) produced 14.23 t ha1 y1 respectively. The best results of Platanus
Biomass
species and hybrids were at the vicinity of 10 t ha1 y1. Clones selected under a combi-
Breeding
nation of higher temperature and drier condition regimes reflecting the Mediterranean
Greece
field conditions will be valuable in future breeding under a changing climate and increased
Populus
energy needs. The high genetic diversity of the virtually unattached local genetic reserve
Platanus
can provide even from the initial breeding cycles great opportunities for genetic improvement and significant genetic gains. ª 2010 Elsevier Ltd. All rights reserved.
1.
Introduction
In the current environment of renewable energy development one option is the production of energy from fast growing forest trees in short rotation intensive culture plantations (SRIC), called bioenergy feedstocks. SRIC poplar plantations for example can produce 18e20 MJ kg1, an equivalent of about 4.30 m3 of oil per hectare [1]. Based on the commitments of the Kyoto protocol, the White Paper of the European Commission (EC) states that the European (EU15) bioenergy share should grow by 8.5% by the year 2010 and at least half of this increase is expected to come from SRIC energy crops. Exploitation of Europe’s biomass potential is one of the critical
points for the accomplishment of the EU objectives [2]. Furthermore bioenergy feedstocks can also provide chemical and pharmaceutical products and be used in carbon sequestration and phytoremediation. The potential of fast growing forest trees high productivity, coppice ability and ease of vegetative propagation in SRIC plantations has been recognized for over twenty-five years [3]. In Greece, pertinent research followed international trends swiftly [4]. As in other countries it capitalized on an earlier well-developed poplar breeding program [5]. Over this quarter of a century period notable results have been achieved in various facets of pertinent research. Unfortunately though, most of them have been published in what is being
* Tel.: þ30 2310 992778; fax: þ30 2310 344693. E-mail address: [email protected] 0961-9534/$ e see front matter ª 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.biombioe.2010.06.012
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collectively known as ‘grey literature’. In this case it involves mainly publications in national conference proceedings, or university scientific annals, international conference proceedings of restricted circulation, independent publications of research institutes, university laboratories, state agencies, etc. Most of these publications have been written in Greek introducing an additional difficulty in the communication of research results to an international scientific audience. The objective of this review is to provide a critical analysis of this literature and identify future goals.
1.1.
Present state of energy balance in Greece
Greece is heavily dependent on an offshore energy supply. The energy import dependency reaches 72.7% compared to 50.1% of EU-27. Domestic production is heavily dependent on solid fuels (84%), mainly lignite for electricity production, which is leading to high CO2 intensity values. Renewable sources account for about 15% of total domestic production, two-thirds of which is based on major hydroelectric power stations [6]. Biomass covers about 4% of the remaining renewable energy portion or 0.2% of the total domestic energy supply [7]. The EU renewable Energy Sources Directive 2001/ 77/EC asserts that Greece must produce 20.1% of its total electricity production from renewable sources including hydroelectricity [8]. The EC directive also mandates that by 2010 at least 5.75% of transport fuel used in Greece and 1.2% of generated electricity originate from biomass. Greece is behind reaching this goal, but according to a recent study [9], this target could be met if some 3700 km2 are cultivated with energy plants. This area can be secured as a result of the EU Common Agricultural Policy crop restructuring directives; however some form of subsidies may be needed in order to ensure long-term economic viability [9]. The contribution of fast growing forest species to the above goal can be significant. Abandoned and marginal agricultural lands could be employed in addition to agricultural areas under crop conversion.
1.2.
Fast growing forest tree species in Greece
The most important fast growing forest tree species in Greece are poplars, willows, plane trees, the naturalized black locust and exotic eucalypt species. There are three native poplar species in Greece, Populus alba, Populus nigra, P. tremula and one interspecific hybrid P. alba x tremula (P. x canescens). In addition, two exotic species (Populus deltoides, P. trichocarpa) and one interspecific hybrid (P. x euramericana) important for biomass production have been introduced. All of the native and introduced species and hybrids are interesting for biomass production especially as parents of highly productive interspecific clones. The distribution of the native species is country-wide, mainly in riparian ecosystems. The total area planted with poplars in Greece is about 17,600 ha, of which 16,100 ha (91%) in plantations and the rest is devoted to soil stabilization or amenity purposes [10]. Poplar culture is mainly dedicated thus far to lumber production. Eleven willow species are native in Greece: Salix alba, Salix. amygdalina, Salix. caprea, Salix. cinerea, Salix. incana, Salix. fragilis, Salix. pentandra, Salix. purpurea, Salix. aurita, Salix.
xanthycola and Salix. viminalis. They are mainly found in riparian ecosystems and messic sites, while most species have a country-wide distribution. In addition, Salix babylonica has been introduced. Among the native species, interest for biomass production present S. viminalis and S. purpurea, while S. cinerea and S. caprea are interesting as parents in highly productive hybrids [11,12]. There is one native plane tree species, Platanus orientalis. The species presents a country-wide distribution, located mainly in riparian ecosystems and messic sites. Platanus occidentalis has been introduced. Both species and their interspecific hybrid Platanus x acerifolia are interesting for biomass production [13]. Black locust (Robinia pseudoacacia L.) was introduced in Greece more than 200 years ago and today it has become a naturalized species. Originally it was used for ornamental and soil stabilization purposes. Currently it is being used for wood and fodder biomass production, soil improvement and restoration of disturbed ecosystems. As a very hardy species it has the advantage as possibly being the only option in areas having very poor conditions. The total planted area is about 11,000 ha; approximately 9000 ha form plantations and afforestations. Eucalypt species have been introduced in Greece in the middle of the 19th century. About 50 species, varieties and clones have been evaluated primarily for wood production, but also for biomass [14]. Eucalypts have been planted as amenity trees for landscaping purposes and are also present in experimental plantations, but are neither considered a naturalized, nor a plantation species in the country.
2.
Materials and methods
Greece presents a very wide and diverse range of landscapes, climatic and soil conditions. For an optimal use of all available areas, different species have to be employed. Five genera have been the focus of pertinent research: Populus, Platanus, Robinia and Salix and Eucalyptus [13e15]. Field test evaluations in pertinent studies employed a variety of parameters and various units of measurements: dry weight (g, kg, t), height (m, cm), DBH (cm, mm), growth increment (cm), stem number, volume (m3), mean circular area at DBH (cm2, m2), area (ha, test site total), time (per year, per rotation period). Rotation periods ranged from 2 to 5 years and spacing varied between 0.5 0.5 m and 4.0 4.0 m. Clonal mix plantations were primarily of the monoclonal block type. Production has been estimated as weight on a plant or test site basis, or by a combination of weight and area parameters. In order to achieve a uniform presentation of the results that would allow direct comparisons wherever possible, all available data have been converted to t ha1 y1. Weight in all cases refers to a bone dry tonne, i.e. biomass without moisture. Field test sites were representative of typical areas available for the respective species plantations. No fertilization was used. Irrigation was generally not employed and was restricted to dry sites and mostly to the first summer after plantation establishment. Therefore, test results in principal reflect the potential of these species and clones in operational plantations.
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When plant material was evaluated in different tests and/ or at subsequent harvests of the same plantations, mean values and associated standard deviations are given. In Populus and Platanus only clones or families evaluated in more than one experimental plantation and/or for more than one rotation period are reported. This rule was not followed for Salix, Robinia and Eucalyptus, because available results were more limited. In total, 27 experimental plantations (10 poplar, nine plane tree, two black locust, one willow and five eucalypt) established and evaluated in the period of the past four decades have been considered.
3.
Results and discussion
3.1.
Populus L.
period and stump replacement is suggested [13]. A total of 20 clones that came out of the Greek breeding program have been released; nine clones are currently in production nurseries: HeX/3, He-X/10, He-K/7, He-90 (“Thessaloniki-1”), He-X/34, R-440, R-75, He-Axios-1 and He-Sparta-1 [10,15]. These clones have been included in a static ex-situ conservation plantation (Table 1) and their DNA fingerprints have been identified [27]. The meta-analysis performed in this communication (Table 2), suggests that two clones of the Greek breeding program (He-X/ 3, He-X/10), that besides biomass also performed well in wood volume evaluations [16], should be used more extensively. In addition, some of the released clones should be phased out of production and replaced by new ones.
3.2.
More than 100 intra and interspecific crosses that included more than 40 genetic entries (species, varieties and clones) had taken place [16]. Species, clones and interspecific hybrids (F1, F2 and backcrosses) have been tested in multisite experiments. A total of 121 clones are currently tested in eight clonal field experiments for biomass or wood production, while 163 clones are present in a gene bank and a clonal archive (Table 1). The clones tested originated from: P. alba, P. deltoides, P. x euramericana, P. nigra P. nigra cv. italica, P. nigra var. thevestina P. nigra cv. italica, P. nigra var. pubescens P. nigra cv. italica, P. alba x tremula P. tremula cv. spartiatica, P. deltoides var. missouriensis P. nigra cv. italica and P. deltoides P. trichocarpa. Some well known and extensively used, on an international basis, poplar clones were also included in these tests. The reason was two-fold: to compare their performance with the Greek clones and to assess their potential and growth under the local climatic and soil conditions. Results presented herein concern only clones with an average production of more than 10 t ha1 y1 (Table 2). The best clone was the well known P. x euramericana I-455 with an average production of 16.54 t ha1 y1, followed by I-214 with an average production of 14.40 t ha1 y1. Two clones of the Greek breeding program also performed very well. Both were crosses of P. deltoides var. missouriensis and P. nigra cv. italica: He-X/3 produced 14.23 t ha1 y1 and He-X/10 produced 11.13 t ha1 y1 (Table 2). Clonal differences were statistically significant in individual tests; however their average performance differences were less pronounced (Table 2). In total, eight clones produced more than 10 t ha1 y1. Two of these clones originated from the Greek breeding program (Table 2). Besides production, several other facets of a breeding program have been advanced. Clones that perform best under particular spacing (ranging from 1 m 1 m to 4 m 4 m) have been selected [13]. The increased production from coppice versus seedling plantations of the same clone has been demonstrated and reached up to 40% [17]. Inter-genotypic competition studies identified clones that perform better when in iso-competition (in monoclonal block plantations) and clones better performing in allo-competition (in clonal mix plantations) [18]. These plantations produced more biomass than the respective sum of monoclonal plantations, while this performance was maintained after three subsequent harvests [18,19]. In general, production falls after the fourth rotation
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Platanus L.
Breeding efforts on the plane tree have started in late 1970s [24]. Breeding was concentrated on biomass production. It involved development of full-sib and open-pollinated families of P. orientalis, P. occidentalis and P. x acerifolia and subsequent testing in multisite experiments for family and clonal selection [13]. At present, nine experimental plantations and one gene bank feature a total of 47 families and 135 clones (Table 3). Results presented herein concern clonal mix and family tests with an average production of more than 6.50 t ha1 y1 (Table 2). P. orientalis family production ranged from 9.79 t ha1 y1 (family POR26) to 6.58 t ha1 y1 (family POR53). The former family presented the highest biomass production compared to family and clonal mix results across both species and hybrids. The second best production was of a P. x acerifolia clonal mix (9.55 t ha1 y1; Table 2). A P. x acerifolia family (PAC01) produced 8.21 t ha1 y1 and ranked in the middle of the respective P. orientalis families (Table 2). Hybrid vigour for P. x acerifolia has been reported [21]. It appears from the present meta-analysis that any heterotic effects are probably the results of overdominance in specific parental combinations. In general, family differences in biomass production were statistically significant in individual tests however their average performance differences across sites and rotation periods were less pronounced (Table 2). The biomass production of coppice versus seedling plantations of the same family was tested for three subsequent rotation periods. Biomass production was increased by an average of about 60% for the first coppice rotation period and by an additional 14% at the second coppice rotation period [13].
3.3.
Salix L.
Breeding efforts on willows focused in the introduced species S. babylonica, where after clonal selection a biomass production experimental plantation was established (Table 2). The production of this plantation at 30 t ha1 y1 [21,28] was very high, comparable to the best clones of major producing European and North-American clones [29]. In effect it was the highest production on a per year and hectare basis reported for all different species and hybrids used in the Greek breeding programs. Nevertheless, in the absence of any additional data, it is not known if this value is reliable. Willows have a high potential for future development of biomass producing clones: they are more tolerant than poplars in a wide variety of
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Table 1 e Clonal tests and ex-situ conservation plantations for poplars (Populus L.) in Greece. Location
Description of plantation
Year of Establishment
No. of clones
Species/hybrids present
Remarks
P. nigra P. nigra var. italica, P. nigra var. thevestina P. nigra var. italica, P. deltoides var. missuriensis P. nigra var. italica, P. deltoides, P. x euramericana P. nigra P. nigra var. italica, P. nigra var. thevestina P. nigra var. italica, P. deltoides P. nigra var. italica, P. deltoides, P. x euramericana P. nigra P. nigra var. italica, P. nigra var. thevestina P. nigra var. italica, P. deltoides var. missuriensis P. nigra var. italica, P. deltoides, P. euramericana P. nigra P. nigra var. italica, P. nigra var. thevestina P. nigra var. italica, P. deltoides var. missuriensis P. nigra var. italica, P. deltoides, P. tremula P. alba cv. spartiatica P. nigra var. thevestina P. nigra var. italica, P. deltoides, P. alba, P. simonii, P. nigra var. pubescens P. nigra var. italica,, P. deltoides var. missuriensis P. nigra var. italica, P. tremula P. alba cv. spartiatica P. deltoides P. nigra var. italica, P. x euramericana P. alba, P. nigra, P. tremula, P. nigra P. nigra var. italica, P. nigra var. thevestina P. nigra var. italica, P. deltoides P. nigra var. italica, P. deltoides, P. x euramericana, P. deltoides P. trichocarpa, P. x euramericana P. x euramericana, Populus deltoides var. missuriensis P. nigra cv. italica P. x euramericana P. nigra P. nigra var. italica, P. nigra var. thevestina P. nigra var. italica, P. deltoides var. missuriensis P. nigra var. italica, P. deltoides, P. x euramericana P. x euramericana, Populus deltoides var. missuriensis P. nigra cv. italica
Growth evaluations
Axios - I
Clonal test
1991
18
Axios - II
Clonal test
1992
18
Axios - III
Clonal test
1993
16
Axios - IV
Clonal test
2000
7
Mikra
Clonal gene bank
1988
19
Peponia Polykastro (Populetum)
Clonal test Clonal test
1989 1967
5 163
Serres
Clonal test
1977
5
Strymon - I Strymon - II
Clonal test Clonal test
1977 1977
5 18
Strymon - III
Clonal test
1997
10
climatic and soil conditions an attribute particularly important under the ensuing climatic change, they present favourable biological attributes and an intact genetic reserve [15,29]. Willow breeding in Greece is in urgent need to explore the local gene pool of species important to biomass production and to investigate further the potential of S. babylonica. The potential through genetic improvement is very promising, since the apparent tremendous genetic diversity distributed over a plethora of willow species provides unique opportunities for genetic manipulation, and intensive breeding.
3.4.
R. pseudoacacia L.
The black locust breeding program has also been limited. A total of 30 clones were evaluated in a R. pseudoacacia, clonal mix experiment and biomass production reached 9.75 t ha1 y1 [26], which was the best result among R. pseudoacacia tests in Greece from a total of three similar tests [26,30,31]. In R. pseudoacacia var. monophylla 9 open-pollinated families and 12 clones were tested [32]. Results presented consider only clones with an average production of more than 3.50 t ha1 y1 (Table 2). Biomass production of the R. pseudoacacia var. monophylla clones ranged between 8.98 t ha1 y1 and 3.98 t ha1 y1 (Table 2).
3.5.
EucalyptusL0 Her. spp.
The first eucalypt experimental trials in Greece, established more than 40 years ago, included about 50 species, varieties and
Growth evaluations
Growth evaluations
Growth evaluations
RAPD fingerprinting
Growth evaluations Growth evaluations
Growth evaluations Growth evaluations Growth evaluations
Growth evaluations
clones that have been evaluated primarily for wood production, but also for biomass [14]. Results indicated as most promising six species: Eucalytpus bicostata, Eucalytpus camaldulensis, Eucalytpus cladocalyx, Eucalytpus dalrympleana, Eucalytpus saligna and Eucalytpus viminalis [21]. A clonal mix multi-species plantation produced an average of 12.00 t ha1 y1 [24]. Further growth evaluations and studies on species ecological requirements taking into account potentially available lands for eucalypt plantations in Greece, have resulted in the selection of three species that combine fast growth and suitability under local conditions: E. bicostata, E. dalrympleana and E. viminalis [14]. A biomass trial that compared the above species, as well as provenances within species depicted significant differences among species and provenances [14]. Other authors propose the use of E. camaldulensis and E. globulus [31,33]. The use of the latter may be questioned since very poor performance has been reported, especially in areas of poor drainage and high pH [14]. The former, according to one report [33], attained a production of 28.00 t ha1 y1 (Table 2); nevertheless this value should be viewed with caution, since it concerns results of a single field test evaluated in three consecutive 2-year rotation periods. As species and clonal selection has not been well advanced, available published results refer to multi-species clonal mix plantations with a production that varies between 8.40 t ha1 y1 and 25.00 t ha1 y1 and an average of 15.13 t ha1 y1 (Table 2). It should be noted that out of the seven species for which biomass production results in Greece are available, four are being considered as serious invasive plants (E. camaldulensis, E. cladocalyx, E. globulus and E. saligna) [35]. Exotic and potentially
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Table 2 e Mean biomass production (t haL1 yL1) of fast growing Populus, Platanus, Robinia, Salix and Eucalyptus tested in experimental plantations in Greece (standard deviation in parentheses). Origin
Production (t ha1 y1)
References
Populus spp. Populus deltoides var. missuriensis P. nigra cv. italica Populus. deltoides var. missuriensis P. nigra cv. italica Populus x euramericana Populus x euramericana Populus x euramericana Populus deltoides Populus deltoides Platanus orientalis Platanus occidentalis Platanus x acerifolia P. orientalis P. orientalis P. orientalis P. orientalis P. orientalis P. orientalis P. orientalis P. orientalis P. orientalis Platanus x acerifolia Robinia pseudoacacia R. pseudoacacia var. monophylla R. pseudoacacia var. monophylla R. pseudoacacia var. monophylla R. pseudoacacia var. monophylla Salix babylonica Eucalytpus camaldulensis Eucalytpus spp.
14.29 (7.29) 14.23 (6.47) 11.13 (5.42) 14.40 (9.24) 10.31 (8.58) 16.54 (3.76) 12.40 (2.26) 10.99 (5.92) 8.74 (3.05) 9.31 (3.18) 9.55 (2.27) 8.33 (2.66) 9.33 (2.10) 9.79 (3.89) 7.87 (1.83) 7.54 (3.05) 8.62 (2.12) 7.94 (1.42) 7.46 (1.48) 6.58 (1.48) 8.21 (2.55) 7.75 (1.70) 8.98 5.82 3.98 2.90 30.00 28.00 15.13 (8.73)
[13,17e20] [10,13,15,17,19,21,22] [13,15,17,19,22] [13,17,19e22] [13,17,19,22] [21] [13,18,19,22] [13,18,19,22] [13,21,23,25] [13,21,23,25] [13,21,24,25] [13,23] [13,23] [13,23] [13,23] [13,23] [13,23] [13,23] [13,23] [13,23] [13,23] [26,30,31] [32] [32] [32] [32] [32] [33] [14,24,30,31,34]
Genetic entry/code Clonal mix He-X/3 He-X/10 I-214 I-262 I-455 R-440 R-75 Clonal mix Clonal mix Clonal mix POR20 POR23 POR26 POR29 POR38 POR39 POR45 POR50 POR53 PAC01 Clonal mix A-7B(6) B-2B(3) A-B(3) A-8A(3) Clonal mix Clonal mix Clonal mix
invasive species, which have not become naturalized in the country, such as eucalypts, may be considered for biomass production in the future only in areas where other options have failed and should be employed with caution.
3.6.
Future breeding
Different species presented notably diverse results with regards to their biomass production. The best poplar clone
Table 3 e Clonal tests and ex-situ conservation plantations for plane tree (Platanus L.) in Greece. Location
Axios - I
Plantation description
Establishment No. of No. of year families clones
1972
Axios - II
Open-pollinated family test Clonal test
1991
24
Axios - III Axios - IV Makrakomi - I Makrakomi - II
Clonal Clonal Clonal Clonal
1992 2000 1972 1972
3 6 124 41
Makrakomi - III Makrakomi - IV
1973 1973
Mikra - I
Clonal biomass test Open-pollinated family test Clonal gene bank
Micra - II
Family test
1991
test test test test
30
22 10
1988
10 9
Species/hybrids present (no. of families/ clones in parentheses)
Remarks
P. orientalis (17), P. occidentalis (11), P. x acerifolia (2) P. orientalis (20), P. orientalis cv. regini (1), P. x acerifolia (3) P. x acerifolia (3) P. orientalis (3), P. x acerifolia (3) P. orientalis (159), P. occidentalis (90) P. orientalis (21), P. orientalis var. cretica (1), P. occidentalis (19) P. orientalis (12), P. occidentalis (10) P. orientalis, (3), P. occidentalis (7)
Growth evaluations
P. orientalis (7), P. orientalis cv. regini (1), P. x acerifolia (3) F2 P. acerifolia (cntrl. poll.; 3), F1 P. x acerifolia (open poll.; 2), P. orientalis (open poll.; 1), P. occidentalis (open poll.; 1), P. orientalis cv. cyprus-larnaka (open poll.; 2)
RAPD fingerprinting
Growth evaluations Growth Growth Growth Growth
evaluations evaluations evaluations evaluations
Growth evaluations Growth evaluations
Growth evaluations
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produced 16.54 t ha1 y1 on the average and the respective values were 9.79 t ha1 y1 for the plane tree and 8.98 t ha1 y1 for black locust. When clonal mix tests were concerned poplar clones produced 14.29 t ha1 y1; plane trees 9.55 t ha1 y1, willows 30 t ha1 y1 and black locust 9.75 t ha1 y1 and eucalypts 28.00 t ha1 y1. All species present a range of biological attributes which are to a large extend complementary. Given the great climatic and soil diversity of Greece, it would be desirable to use most of the available gene pool in biomass breeding programs. Because of the environmental variability described above, clonal deployment strategies form an important and delicate issue. Some key questions that have to be considered include: (a) plantation biological stability and genetic diversity (recourse exploitation, eco-certification, best practise requirements), (b) biotic factors such as resistance or tolerance to diseases and insects, (c) resistance or tolerance to abiotic extremes (climatic change effects), (d) financial viability compared to crop species in marginal or under conversion agricultural lands, (e) plantation energy input/output ratio and carbon balance and (f) ecologically acceptable and environmentally friendly plantation management. The establishment of mixed operational plantations in monoclonal blocks, with 10 genetically different clones, a minimum size of 1 ha/clone at a spacing of 1.0 m 1.0 m has been suggested [36]. Genetic diversity of superior clones should be checked as a means to deduce future multiclonal plantations stability under environmental change [37]. Clone characteristics described as above should be developed through ideotype breeding [38,39]. The use of molecular markers and genomics would be paramount both in DNA fingerprinting [27] and in the early selection of high-yielding clones [40]. Several specific breeding goals have to be addressed in the future, such as: (a) breeding strategies in order to associate under a single genome several gene complexes, (b) study of hybridization, crossabilities and phylogenies, (c) identification of genes associated with growth and biomass production; gene mapping, QTL mapping, association mapping, (d) estimation of standing biomass via non-destructive sampling or allometric measurements, (e) breeding for heavy metal tolerance, use of waste-water sludge in irrigation systems, phytoremediation, (f) relationship among heterozygosity, heterosis, growth and biomass production and (g) functional genomics of biomass production.
4.
Conclusions
In conclusion, the Greek breeding programs have resulted in the development of several poplar, plane tree, black locust, willow and eucalypt clones that have been selected under a combination of higher temperature and drier condition regimes reflecting the Mediterranean field conditions. Two high-yielding poplar clones from the local breeding program present growth comparable to the widely used Euramerican clones. Biomass breeding under a changing climate and increased energy needs can employ this genetic material in new comparative tests or utilize it in new crossing schemes. At the same time these clones can be used in operational plantations at a higher rate. Evidently the concept of
establishing SRIC biomass plantations at a notable scale involves a significant amount of multifaceted research, which should be based, but not limited, to the development and maintenance of a strong breeding program. The high genetic diversity of the effectively intact local plant material can present even from the initial breeding cycles great opportunities for genetic improvement and significant genetic gains.
references
[1] Dickmann DI, Isebrands JG, Eckenwalder JE, Richardson J. Poplar culture in North America. Ottawa: NRC Research Press, National Research Council of Canada; 2001. 539 pp. [2] Eriksson K, Nilsson LJ. Assessment of the potential biomass supply in Europe using a resource focused approach. Biomass Bioenerg 2006;30:1e15. [3] Siren G. Present stage of energy forestry research in Sweden. In: Proceedings international forestry energy meeting, Umea, Sweden; 1981. pp. 106e17. [4] Panetsos KP. Maximization of biomass production from forest species plantations. In: Proceedings 1st national renewable energy conference, Thessaloniki. Thessaloniki: Institute of Solar Technology; 1982. p. 209e19. [5] Panetsos KP. Artificial hybrids between native Populus nigra L. var. pubescens Parlat and introduced species and clones. Athens: Athens Forest Research Institute No. 18; 1967. 49 pp. [6] Energy fact sheet e Greece, http://ec.europa.eu/energy/ energy_policy/facts.en.htm>; 2009 (March 10, 2010). [7] Biofuels in Greece, final report. Thessaloniki: Biofuels Technology Platform Advisory Committee, Thessaly Regional Innovation Pole; 2008. 42 pp. [8] Journal of the European Union (OJL283/27.10.2001). Electricity production from RES. Directive 2001/77/EC of the European Parliament and the Council on the promotion of the electricity produced from renewable energy sources in the international electricity market. Brussels; 2001. 8 p. [9] INASO-Institute for rural development and cooperative economy study, http://www.paseges.gr/portal/cl/tn/INASO/ co/; 2009 (May 30, 2009). [10] Avtzis N, Diamantis S, Koukos P, Panetsos KP, Tsiontsis A. Poplar culture manual. Athens: Hellenic Ministry of Agriculture; 1999. 96. [11] Larsson S. Genetic improvement of willow for short rotation coppice. Biomass Bioenerg 1998;15:23e6. [12] Hofmann-Schiele C, Jug A, Makeschin F, Rehfuess KE. Short-rotation plantations of balsam poplars, aspens and willows on former arable land in the Federal Republic of Germany. I. Site-growth relationships. For Ecol Manag 1999;121:41e55. [13] Panetsos KP, Alizoti PG, Scaltsoyiannes AB, Aravanopoulos FA. Biomass production results from fast growing forest species. In: Panayiotou PH, editor. Proceedings national renewable energy network conference. Thessaloniki: National Agricultural Research Foundation; 1996. p. 23e32. [14] Panetsos KP. The biomass production potential of fast growing forest species plantations for energy purposes. In: Panayiotou PH, editor. Proceedings national renewable energy network conference. Karpenisi: Institute of Rural Economy; 1998. p. 87e100. [15] Aravanopoulos FA. Panetsos KP. Contribution of genetics in the breeding of poplars and willows. In: Proceedings 7th national conference Hellenic forestry society, Thessaloniki; 1996. pp. 173e84.
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[16] Panetsos KP. Genetic improvement of poplar in Greece: achievements. In: Proceedings Hellenic forestry society meeting, Thessaloniki; 1994. pp. 93e100. [17] Panetsos KP, Scaltsoyiannes A. Biomass production of short rotation poplar clonal plantations. In: 2nd national renewable energy conference, Thessaloniki; 1985; 2:647e55. [18] Panetsos KP, Alizoti P, Scaltsoyiannes A. Biomass production of poplar clonal plantations under a two year rotation period. In: Proceedings 4th national renewable energy conference, Athens; 1992; 2:362e70. [19] Panetsos KP, Alizoti PG, Netsikas E, Foti DE, Alexandri AK. Biomass production of selected poplar clones. In: Proceedings 5th national renewable energy conference, vol. 3. Athens: Democritus National Research Centre; 1996. p. 204e16. [20] Spanos KA, Tsialtas I, Alizoti PG, Aravanopoulos FA. Biomass production from a short rotation poplar experimental plantation. Scientific Ann Fac For Nat Environ Aristotle Univ Thessaloniki 2003;40:863e72. [21] Panetsos KP, Kyritsis S. Short rotation biomass plantations in Greece. In: Hummel FC, Pulz W, Grassi G, editors. Biomass forestry in Europe: a strategy for the future. London: Elsevier; 1988. p. 373e401. [22] Panetsos KP, Alizoti PG. Biomass production from monoclonal and mixed clonal plantations. In: Proceedings 5th national renewable energy conference, vol. 3. Athens: National Research Centre Democritus; 1996. p. 201e4. [23] Panetsos KP. Biomass yield of short rotation Platanus species in Greece. In: Grassi G, Gosse G, dos Santos G, editors. Biomass for energy and industry. London: Elsevier; 1989. p. 10e6. [24] Panetsos KP. Biomass yield of short rotation Platanus species in Greece. In: Commercialization of production of Mediterranean climatic regions. The Hague: W. Junk Publ.; 1981. p. 235e8. [25] Panetsos KP, Zaragotas D. Biomass production from forest tree species plantations. In: Energy from biomass in Greece. Athens: NationalPolytechnic University of Athens; 1989. p. 67e80. [26] Kyritsis S, Dalianis K, Mellidis B. Biomass production from black locust. In: Proceedings 5th national conference Hellenic scientific society for plant breeding, Volos; 1994. pp. 256e9. [27] Vaxevanidou Z, Aravanopoulos FA. DNA fingerprinting of selected poplar clones based on randomly amplified DNA (RAPD) markers. In: Proceedings 9th National conference Hellenic scientific society for plant breeding, Thessaloniki; 2002. pp. 420e6.
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[28] Panetsos KP. Biomass production from fast growing forest tree species. In: Proceedings 3rd national conference of renewable energy, vol. 2. Thessaloniki: Greek Productivity Centre; 1988. p. 29e36. [29] Zsuffa L, Aravanopoulos FA. Genetics and breeding of Salicaceae. In: Recent developments in poplar selection and propagation. Hann Munden: Institute of Forest Tree Breeding Publ.; 1989. p. 1e17. [30] Markidis M, Namatov I, Panoutsou C. Research and technology development in the field of energy crops in Greece. In: Proceedings 1st world conference on biomass for energy and industry, vol. 2. London: James and James Publ.; 2001. p. 1502e5. [31] Kittas K. Biofuels and energy crops. In: Proceedings 2nd national alternative fuels and biofuels conference, Plastira Lake, Karditsa; 2007. 41 p. [32] Dini-Papanastasi O. Effects of clonal selection on biomass production and quality of Robinia pseudoacacia var. monophylla Carr. For Ecol Manag 2008;256:849e54. [33] Christou M, Alexopoulou E, Mardikis M, Namatov I. Perspectives on the introduction of energy crops in Greek agriculture. In: Proceedings 3rd national renewable energy Congress, Athens; 2005. pp. 1e11. [34] Danalatos N. Biomass. In: Proceedings “Biofuel Production in the Thessaly Region” Conference, Volos; 2008. 23 p. [35] Anonymous. Invasive and exotic species, http://www. invasive.org/browse/genus.cfm?id¼Eucalyptus; 2010 (March 10, 2010). [36] Aravanopoulos FA, Alizoti PG, Scaltsoyiannes A. Mixed or pure clonal plantations for biomass production? How many clones and why. In: Panayiotou PH, editor. Proceedings national renewable energy network conference. Karpenisi: Institute of Rural Economy; 1998. p. 155e66. [37] Aravanopoulos FA, Kim KH, Zsuffa L. Genetic diversity of superior Salix clones selected for intensive forestry plantations. Biomass Bioenerg 1999;16:249e55. [38] Aravanopoulos FA. Poplar (Populus L.) ideotype breeding for employment in short rotation intensive forestry. Scientific Ann Fac For Nat Environ Aristotle Univ Thessaloniki 1997;40: 83e102. [39] Cheliak WM, Aravanopoulos FA, editors. Tree-Form Catalogue, international energy Agency/Bioenergy Agreement and Faculty of forestry. Toronto: University of Toronto; 1991. p. 50. [40] Aravanopoulos FA, Zsuffa L. Heterozygosity and biomass production in Salix eriocephala. Heredity 1998;81:396e403.
Available at www.sciencedirect.com
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Review
Breeding of fast growing forest tree species for biomass production in Greece F.A. Aravanopoulos* Laboratory of Forest Genetics & Tree Breeding, Faculty of Forestry and Natural Environment, PO Box 238, Aristotle University of Thessaloniki, 54124 Thessaloniki, Greece
article info
abstract
Article history:
The purpose of this review is to provide a critical analysis of the literature regarding the
Received 13 July 2009
breeding of fast growing forest tree species dedicated to biomass production in Greece and
Received in revised form
to identify future goals. The main genera employed in pertinent research which show the
30 April 2010
most promising results for operational plantations belong to Populus spp. and Platanus spp.
Accepted 17 June 2010
The best poplar clone (P. x euramericana I-455) produced 16.54 t ha1 y1 dry weight averaged over different experimental plantations and rotation periods, while the best clone derived from the Greek breeding program (Populus deltoides var. missouriensis Populus nigra
Keywords:
var. pubescens He-X/3) produced 14.23 t ha1 y1 respectively. The best results of Platanus
Biomass
species and hybrids were at the vicinity of 10 t ha1 y1. Clones selected under a combi-
Breeding
nation of higher temperature and drier condition regimes reflecting the Mediterranean
Greece
field conditions will be valuable in future breeding under a changing climate and increased
Populus
energy needs. The high genetic diversity of the virtually unattached local genetic reserve
Platanus
can provide even from the initial breeding cycles great opportunities for genetic improvement and significant genetic gains. ª 2010 Elsevier Ltd. All rights reserved.
1.
Introduction
In the current environment of renewable energy development one option is the production of energy from fast growing forest trees in short rotation intensive culture plantations (SRIC), called bioenergy feedstocks. SRIC poplar plantations for example can produce 18e20 MJ kg1, an equivalent of about 4.30 m3 of oil per hectare [1]. Based on the commitments of the Kyoto protocol, the White Paper of the European Commission (EC) states that the European (EU15) bioenergy share should grow by 8.5% by the year 2010 and at least half of this increase is expected to come from SRIC energy crops. Exploitation of Europe’s biomass potential is one of the critical
points for the accomplishment of the EU objectives [2]. Furthermore bioenergy feedstocks can also provide chemical and pharmaceutical products and be used in carbon sequestration and phytoremediation. The potential of fast growing forest trees high productivity, coppice ability and ease of vegetative propagation in SRIC plantations has been recognized for over twenty-five years [3]. In Greece, pertinent research followed international trends swiftly [4]. As in other countries it capitalized on an earlier well-developed poplar breeding program [5]. Over this quarter of a century period notable results have been achieved in various facets of pertinent research. Unfortunately though, most of them have been published in what is being
* Tel.: þ30 2310 992778; fax: þ30 2310 344693. E-mail address: [email protected] 0961-9534/$ e see front matter ª 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.biombioe.2010.06.012
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collectively known as ‘grey literature’. In this case it involves mainly publications in national conference proceedings, or university scientific annals, international conference proceedings of restricted circulation, independent publications of research institutes, university laboratories, state agencies, etc. Most of these publications have been written in Greek introducing an additional difficulty in the communication of research results to an international scientific audience. The objective of this review is to provide a critical analysis of this literature and identify future goals.
1.1.
Present state of energy balance in Greece
Greece is heavily dependent on an offshore energy supply. The energy import dependency reaches 72.7% compared to 50.1% of EU-27. Domestic production is heavily dependent on solid fuels (84%), mainly lignite for electricity production, which is leading to high CO2 intensity values. Renewable sources account for about 15% of total domestic production, two-thirds of which is based on major hydroelectric power stations [6]. Biomass covers about 4% of the remaining renewable energy portion or 0.2% of the total domestic energy supply [7]. The EU renewable Energy Sources Directive 2001/ 77/EC asserts that Greece must produce 20.1% of its total electricity production from renewable sources including hydroelectricity [8]. The EC directive also mandates that by 2010 at least 5.75% of transport fuel used in Greece and 1.2% of generated electricity originate from biomass. Greece is behind reaching this goal, but according to a recent study [9], this target could be met if some 3700 km2 are cultivated with energy plants. This area can be secured as a result of the EU Common Agricultural Policy crop restructuring directives; however some form of subsidies may be needed in order to ensure long-term economic viability [9]. The contribution of fast growing forest species to the above goal can be significant. Abandoned and marginal agricultural lands could be employed in addition to agricultural areas under crop conversion.
1.2.
Fast growing forest tree species in Greece
The most important fast growing forest tree species in Greece are poplars, willows, plane trees, the naturalized black locust and exotic eucalypt species. There are three native poplar species in Greece, Populus alba, Populus nigra, P. tremula and one interspecific hybrid P. alba x tremula (P. x canescens). In addition, two exotic species (Populus deltoides, P. trichocarpa) and one interspecific hybrid (P. x euramericana) important for biomass production have been introduced. All of the native and introduced species and hybrids are interesting for biomass production especially as parents of highly productive interspecific clones. The distribution of the native species is country-wide, mainly in riparian ecosystems. The total area planted with poplars in Greece is about 17,600 ha, of which 16,100 ha (91%) in plantations and the rest is devoted to soil stabilization or amenity purposes [10]. Poplar culture is mainly dedicated thus far to lumber production. Eleven willow species are native in Greece: Salix alba, Salix. amygdalina, Salix. caprea, Salix. cinerea, Salix. incana, Salix. fragilis, Salix. pentandra, Salix. purpurea, Salix. aurita, Salix.
xanthycola and Salix. viminalis. They are mainly found in riparian ecosystems and messic sites, while most species have a country-wide distribution. In addition, Salix babylonica has been introduced. Among the native species, interest for biomass production present S. viminalis and S. purpurea, while S. cinerea and S. caprea are interesting as parents in highly productive hybrids [11,12]. There is one native plane tree species, Platanus orientalis. The species presents a country-wide distribution, located mainly in riparian ecosystems and messic sites. Platanus occidentalis has been introduced. Both species and their interspecific hybrid Platanus x acerifolia are interesting for biomass production [13]. Black locust (Robinia pseudoacacia L.) was introduced in Greece more than 200 years ago and today it has become a naturalized species. Originally it was used for ornamental and soil stabilization purposes. Currently it is being used for wood and fodder biomass production, soil improvement and restoration of disturbed ecosystems. As a very hardy species it has the advantage as possibly being the only option in areas having very poor conditions. The total planted area is about 11,000 ha; approximately 9000 ha form plantations and afforestations. Eucalypt species have been introduced in Greece in the middle of the 19th century. About 50 species, varieties and clones have been evaluated primarily for wood production, but also for biomass [14]. Eucalypts have been planted as amenity trees for landscaping purposes and are also present in experimental plantations, but are neither considered a naturalized, nor a plantation species in the country.
2.
Materials and methods
Greece presents a very wide and diverse range of landscapes, climatic and soil conditions. For an optimal use of all available areas, different species have to be employed. Five genera have been the focus of pertinent research: Populus, Platanus, Robinia and Salix and Eucalyptus [13e15]. Field test evaluations in pertinent studies employed a variety of parameters and various units of measurements: dry weight (g, kg, t), height (m, cm), DBH (cm, mm), growth increment (cm), stem number, volume (m3), mean circular area at DBH (cm2, m2), area (ha, test site total), time (per year, per rotation period). Rotation periods ranged from 2 to 5 years and spacing varied between 0.5 0.5 m and 4.0 4.0 m. Clonal mix plantations were primarily of the monoclonal block type. Production has been estimated as weight on a plant or test site basis, or by a combination of weight and area parameters. In order to achieve a uniform presentation of the results that would allow direct comparisons wherever possible, all available data have been converted to t ha1 y1. Weight in all cases refers to a bone dry tonne, i.e. biomass without moisture. Field test sites were representative of typical areas available for the respective species plantations. No fertilization was used. Irrigation was generally not employed and was restricted to dry sites and mostly to the first summer after plantation establishment. Therefore, test results in principal reflect the potential of these species and clones in operational plantations.
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When plant material was evaluated in different tests and/ or at subsequent harvests of the same plantations, mean values and associated standard deviations are given. In Populus and Platanus only clones or families evaluated in more than one experimental plantation and/or for more than one rotation period are reported. This rule was not followed for Salix, Robinia and Eucalyptus, because available results were more limited. In total, 27 experimental plantations (10 poplar, nine plane tree, two black locust, one willow and five eucalypt) established and evaluated in the period of the past four decades have been considered.
3.
Results and discussion
3.1.
Populus L.
period and stump replacement is suggested [13]. A total of 20 clones that came out of the Greek breeding program have been released; nine clones are currently in production nurseries: HeX/3, He-X/10, He-K/7, He-90 (“Thessaloniki-1”), He-X/34, R-440, R-75, He-Axios-1 and He-Sparta-1 [10,15]. These clones have been included in a static ex-situ conservation plantation (Table 1) and their DNA fingerprints have been identified [27]. The meta-analysis performed in this communication (Table 2), suggests that two clones of the Greek breeding program (He-X/ 3, He-X/10), that besides biomass also performed well in wood volume evaluations [16], should be used more extensively. In addition, some of the released clones should be phased out of production and replaced by new ones.
3.2.
More than 100 intra and interspecific crosses that included more than 40 genetic entries (species, varieties and clones) had taken place [16]. Species, clones and interspecific hybrids (F1, F2 and backcrosses) have been tested in multisite experiments. A total of 121 clones are currently tested in eight clonal field experiments for biomass or wood production, while 163 clones are present in a gene bank and a clonal archive (Table 1). The clones tested originated from: P. alba, P. deltoides, P. x euramericana, P. nigra P. nigra cv. italica, P. nigra var. thevestina P. nigra cv. italica, P. nigra var. pubescens P. nigra cv. italica, P. alba x tremula P. tremula cv. spartiatica, P. deltoides var. missouriensis P. nigra cv. italica and P. deltoides P. trichocarpa. Some well known and extensively used, on an international basis, poplar clones were also included in these tests. The reason was two-fold: to compare their performance with the Greek clones and to assess their potential and growth under the local climatic and soil conditions. Results presented herein concern only clones with an average production of more than 10 t ha1 y1 (Table 2). The best clone was the well known P. x euramericana I-455 with an average production of 16.54 t ha1 y1, followed by I-214 with an average production of 14.40 t ha1 y1. Two clones of the Greek breeding program also performed very well. Both were crosses of P. deltoides var. missouriensis and P. nigra cv. italica: He-X/3 produced 14.23 t ha1 y1 and He-X/10 produced 11.13 t ha1 y1 (Table 2). Clonal differences were statistically significant in individual tests; however their average performance differences were less pronounced (Table 2). In total, eight clones produced more than 10 t ha1 y1. Two of these clones originated from the Greek breeding program (Table 2). Besides production, several other facets of a breeding program have been advanced. Clones that perform best under particular spacing (ranging from 1 m 1 m to 4 m 4 m) have been selected [13]. The increased production from coppice versus seedling plantations of the same clone has been demonstrated and reached up to 40% [17]. Inter-genotypic competition studies identified clones that perform better when in iso-competition (in monoclonal block plantations) and clones better performing in allo-competition (in clonal mix plantations) [18]. These plantations produced more biomass than the respective sum of monoclonal plantations, while this performance was maintained after three subsequent harvests [18,19]. In general, production falls after the fourth rotation
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Platanus L.
Breeding efforts on the plane tree have started in late 1970s [24]. Breeding was concentrated on biomass production. It involved development of full-sib and open-pollinated families of P. orientalis, P. occidentalis and P. x acerifolia and subsequent testing in multisite experiments for family and clonal selection [13]. At present, nine experimental plantations and one gene bank feature a total of 47 families and 135 clones (Table 3). Results presented herein concern clonal mix and family tests with an average production of more than 6.50 t ha1 y1 (Table 2). P. orientalis family production ranged from 9.79 t ha1 y1 (family POR26) to 6.58 t ha1 y1 (family POR53). The former family presented the highest biomass production compared to family and clonal mix results across both species and hybrids. The second best production was of a P. x acerifolia clonal mix (9.55 t ha1 y1; Table 2). A P. x acerifolia family (PAC01) produced 8.21 t ha1 y1 and ranked in the middle of the respective P. orientalis families (Table 2). Hybrid vigour for P. x acerifolia has been reported [21]. It appears from the present meta-analysis that any heterotic effects are probably the results of overdominance in specific parental combinations. In general, family differences in biomass production were statistically significant in individual tests however their average performance differences across sites and rotation periods were less pronounced (Table 2). The biomass production of coppice versus seedling plantations of the same family was tested for three subsequent rotation periods. Biomass production was increased by an average of about 60% for the first coppice rotation period and by an additional 14% at the second coppice rotation period [13].
3.3.
Salix L.
Breeding efforts on willows focused in the introduced species S. babylonica, where after clonal selection a biomass production experimental plantation was established (Table 2). The production of this plantation at 30 t ha1 y1 [21,28] was very high, comparable to the best clones of major producing European and North-American clones [29]. In effect it was the highest production on a per year and hectare basis reported for all different species and hybrids used in the Greek breeding programs. Nevertheless, in the absence of any additional data, it is not known if this value is reliable. Willows have a high potential for future development of biomass producing clones: they are more tolerant than poplars in a wide variety of
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Table 1 e Clonal tests and ex-situ conservation plantations for poplars (Populus L.) in Greece. Location
Description of plantation
Year of Establishment
No. of clones
Species/hybrids present
Remarks
P. nigra P. nigra var. italica, P. nigra var. thevestina P. nigra var. italica, P. deltoides var. missuriensis P. nigra var. italica, P. deltoides, P. x euramericana P. nigra P. nigra var. italica, P. nigra var. thevestina P. nigra var. italica, P. deltoides P. nigra var. italica, P. deltoides, P. x euramericana P. nigra P. nigra var. italica, P. nigra var. thevestina P. nigra var. italica, P. deltoides var. missuriensis P. nigra var. italica, P. deltoides, P. euramericana P. nigra P. nigra var. italica, P. nigra var. thevestina P. nigra var. italica, P. deltoides var. missuriensis P. nigra var. italica, P. deltoides, P. tremula P. alba cv. spartiatica P. nigra var. thevestina P. nigra var. italica, P. deltoides, P. alba, P. simonii, P. nigra var. pubescens P. nigra var. italica,, P. deltoides var. missuriensis P. nigra var. italica, P. tremula P. alba cv. spartiatica P. deltoides P. nigra var. italica, P. x euramericana P. alba, P. nigra, P. tremula, P. nigra P. nigra var. italica, P. nigra var. thevestina P. nigra var. italica, P. deltoides P. nigra var. italica, P. deltoides, P. x euramericana, P. deltoides P. trichocarpa, P. x euramericana P. x euramericana, Populus deltoides var. missuriensis P. nigra cv. italica P. x euramericana P. nigra P. nigra var. italica, P. nigra var. thevestina P. nigra var. italica, P. deltoides var. missuriensis P. nigra var. italica, P. deltoides, P. x euramericana P. x euramericana, Populus deltoides var. missuriensis P. nigra cv. italica
Growth evaluations
Axios - I
Clonal test
1991
18
Axios - II
Clonal test
1992
18
Axios - III
Clonal test
1993
16
Axios - IV
Clonal test
2000
7
Mikra
Clonal gene bank
1988
19
Peponia Polykastro (Populetum)
Clonal test Clonal test
1989 1967
5 163
Serres
Clonal test
1977
5
Strymon - I Strymon - II
Clonal test Clonal test
1977 1977
5 18
Strymon - III
Clonal test
1997
10
climatic and soil conditions an attribute particularly important under the ensuing climatic change, they present favourable biological attributes and an intact genetic reserve [15,29]. Willow breeding in Greece is in urgent need to explore the local gene pool of species important to biomass production and to investigate further the potential of S. babylonica. The potential through genetic improvement is very promising, since the apparent tremendous genetic diversity distributed over a plethora of willow species provides unique opportunities for genetic manipulation, and intensive breeding.
3.4.
R. pseudoacacia L.
The black locust breeding program has also been limited. A total of 30 clones were evaluated in a R. pseudoacacia, clonal mix experiment and biomass production reached 9.75 t ha1 y1 [26], which was the best result among R. pseudoacacia tests in Greece from a total of three similar tests [26,30,31]. In R. pseudoacacia var. monophylla 9 open-pollinated families and 12 clones were tested [32]. Results presented consider only clones with an average production of more than 3.50 t ha1 y1 (Table 2). Biomass production of the R. pseudoacacia var. monophylla clones ranged between 8.98 t ha1 y1 and 3.98 t ha1 y1 (Table 2).
3.5.
EucalyptusL0 Her. spp.
The first eucalypt experimental trials in Greece, established more than 40 years ago, included about 50 species, varieties and
Growth evaluations
Growth evaluations
Growth evaluations
RAPD fingerprinting
Growth evaluations Growth evaluations
Growth evaluations Growth evaluations Growth evaluations
Growth evaluations
clones that have been evaluated primarily for wood production, but also for biomass [14]. Results indicated as most promising six species: Eucalytpus bicostata, Eucalytpus camaldulensis, Eucalytpus cladocalyx, Eucalytpus dalrympleana, Eucalytpus saligna and Eucalytpus viminalis [21]. A clonal mix multi-species plantation produced an average of 12.00 t ha1 y1 [24]. Further growth evaluations and studies on species ecological requirements taking into account potentially available lands for eucalypt plantations in Greece, have resulted in the selection of three species that combine fast growth and suitability under local conditions: E. bicostata, E. dalrympleana and E. viminalis [14]. A biomass trial that compared the above species, as well as provenances within species depicted significant differences among species and provenances [14]. Other authors propose the use of E. camaldulensis and E. globulus [31,33]. The use of the latter may be questioned since very poor performance has been reported, especially in areas of poor drainage and high pH [14]. The former, according to one report [33], attained a production of 28.00 t ha1 y1 (Table 2); nevertheless this value should be viewed with caution, since it concerns results of a single field test evaluated in three consecutive 2-year rotation periods. As species and clonal selection has not been well advanced, available published results refer to multi-species clonal mix plantations with a production that varies between 8.40 t ha1 y1 and 25.00 t ha1 y1 and an average of 15.13 t ha1 y1 (Table 2). It should be noted that out of the seven species for which biomass production results in Greece are available, four are being considered as serious invasive plants (E. camaldulensis, E. cladocalyx, E. globulus and E. saligna) [35]. Exotic and potentially
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Table 2 e Mean biomass production (t haL1 yL1) of fast growing Populus, Platanus, Robinia, Salix and Eucalyptus tested in experimental plantations in Greece (standard deviation in parentheses). Origin
Production (t ha1 y1)
References
Populus spp. Populus deltoides var. missuriensis P. nigra cv. italica Populus. deltoides var. missuriensis P. nigra cv. italica Populus x euramericana Populus x euramericana Populus x euramericana Populus deltoides Populus deltoides Platanus orientalis Platanus occidentalis Platanus x acerifolia P. orientalis P. orientalis P. orientalis P. orientalis P. orientalis P. orientalis P. orientalis P. orientalis P. orientalis Platanus x acerifolia Robinia pseudoacacia R. pseudoacacia var. monophylla R. pseudoacacia var. monophylla R. pseudoacacia var. monophylla R. pseudoacacia var. monophylla Salix babylonica Eucalytpus camaldulensis Eucalytpus spp.
14.29 (7.29) 14.23 (6.47) 11.13 (5.42) 14.40 (9.24) 10.31 (8.58) 16.54 (3.76) 12.40 (2.26) 10.99 (5.92) 8.74 (3.05) 9.31 (3.18) 9.55 (2.27) 8.33 (2.66) 9.33 (2.10) 9.79 (3.89) 7.87 (1.83) 7.54 (3.05) 8.62 (2.12) 7.94 (1.42) 7.46 (1.48) 6.58 (1.48) 8.21 (2.55) 7.75 (1.70) 8.98 5.82 3.98 2.90 30.00 28.00 15.13 (8.73)
[13,17e20] [10,13,15,17,19,21,22] [13,15,17,19,22] [13,17,19e22] [13,17,19,22] [21] [13,18,19,22] [13,18,19,22] [13,21,23,25] [13,21,23,25] [13,21,24,25] [13,23] [13,23] [13,23] [13,23] [13,23] [13,23] [13,23] [13,23] [13,23] [13,23] [26,30,31] [32] [32] [32] [32] [32] [33] [14,24,30,31,34]
Genetic entry/code Clonal mix He-X/3 He-X/10 I-214 I-262 I-455 R-440 R-75 Clonal mix Clonal mix Clonal mix POR20 POR23 POR26 POR29 POR38 POR39 POR45 POR50 POR53 PAC01 Clonal mix A-7B(6) B-2B(3) A-B(3) A-8A(3) Clonal mix Clonal mix Clonal mix
invasive species, which have not become naturalized in the country, such as eucalypts, may be considered for biomass production in the future only in areas where other options have failed and should be employed with caution.
3.6.
Future breeding
Different species presented notably diverse results with regards to their biomass production. The best poplar clone
Table 3 e Clonal tests and ex-situ conservation plantations for plane tree (Platanus L.) in Greece. Location
Axios - I
Plantation description
Establishment No. of No. of year families clones
1972
Axios - II
Open-pollinated family test Clonal test
1991
24
Axios - III Axios - IV Makrakomi - I Makrakomi - II
Clonal Clonal Clonal Clonal
1992 2000 1972 1972
3 6 124 41
Makrakomi - III Makrakomi - IV
1973 1973
Mikra - I
Clonal biomass test Open-pollinated family test Clonal gene bank
Micra - II
Family test
1991
test test test test
30
22 10
1988
10 9
Species/hybrids present (no. of families/ clones in parentheses)
Remarks
P. orientalis (17), P. occidentalis (11), P. x acerifolia (2) P. orientalis (20), P. orientalis cv. regini (1), P. x acerifolia (3) P. x acerifolia (3) P. orientalis (3), P. x acerifolia (3) P. orientalis (159), P. occidentalis (90) P. orientalis (21), P. orientalis var. cretica (1), P. occidentalis (19) P. orientalis (12), P. occidentalis (10) P. orientalis, (3), P. occidentalis (7)
Growth evaluations
P. orientalis (7), P. orientalis cv. regini (1), P. x acerifolia (3) F2 P. acerifolia (cntrl. poll.; 3), F1 P. x acerifolia (open poll.; 2), P. orientalis (open poll.; 1), P. occidentalis (open poll.; 1), P. orientalis cv. cyprus-larnaka (open poll.; 2)
RAPD fingerprinting
Growth evaluations Growth Growth Growth Growth
evaluations evaluations evaluations evaluations
Growth evaluations Growth evaluations
Growth evaluations
1536
b i o m a s s a n d b i o e n e r g y 3 4 ( 2 0 1 0 ) 1 5 3 1 e1 5 3 7
produced 16.54 t ha1 y1 on the average and the respective values were 9.79 t ha1 y1 for the plane tree and 8.98 t ha1 y1 for black locust. When clonal mix tests were concerned poplar clones produced 14.29 t ha1 y1; plane trees 9.55 t ha1 y1, willows 30 t ha1 y1 and black locust 9.75 t ha1 y1 and eucalypts 28.00 t ha1 y1. All species present a range of biological attributes which are to a large extend complementary. Given the great climatic and soil diversity of Greece, it would be desirable to use most of the available gene pool in biomass breeding programs. Because of the environmental variability described above, clonal deployment strategies form an important and delicate issue. Some key questions that have to be considered include: (a) plantation biological stability and genetic diversity (recourse exploitation, eco-certification, best practise requirements), (b) biotic factors such as resistance or tolerance to diseases and insects, (c) resistance or tolerance to abiotic extremes (climatic change effects), (d) financial viability compared to crop species in marginal or under conversion agricultural lands, (e) plantation energy input/output ratio and carbon balance and (f) ecologically acceptable and environmentally friendly plantation management. The establishment of mixed operational plantations in monoclonal blocks, with 10 genetically different clones, a minimum size of 1 ha/clone at a spacing of 1.0 m 1.0 m has been suggested [36]. Genetic diversity of superior clones should be checked as a means to deduce future multiclonal plantations stability under environmental change [37]. Clone characteristics described as above should be developed through ideotype breeding [38,39]. The use of molecular markers and genomics would be paramount both in DNA fingerprinting [27] and in the early selection of high-yielding clones [40]. Several specific breeding goals have to be addressed in the future, such as: (a) breeding strategies in order to associate under a single genome several gene complexes, (b) study of hybridization, crossabilities and phylogenies, (c) identification of genes associated with growth and biomass production; gene mapping, QTL mapping, association mapping, (d) estimation of standing biomass via non-destructive sampling or allometric measurements, (e) breeding for heavy metal tolerance, use of waste-water sludge in irrigation systems, phytoremediation, (f) relationship among heterozygosity, heterosis, growth and biomass production and (g) functional genomics of biomass production.
4.
Conclusions
In conclusion, the Greek breeding programs have resulted in the development of several poplar, plane tree, black locust, willow and eucalypt clones that have been selected under a combination of higher temperature and drier condition regimes reflecting the Mediterranean field conditions. Two high-yielding poplar clones from the local breeding program present growth comparable to the widely used Euramerican clones. Biomass breeding under a changing climate and increased energy needs can employ this genetic material in new comparative tests or utilize it in new crossing schemes. At the same time these clones can be used in operational plantations at a higher rate. Evidently the concept of
establishing SRIC biomass plantations at a notable scale involves a significant amount of multifaceted research, which should be based, but not limited, to the development and maintenance of a strong breeding program. The high genetic diversity of the effectively intact local plant material can present even from the initial breeding cycles great opportunities for genetic improvement and significant genetic gains.
references
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