Poplar is one of the most important forest trees because of its high economic value. Thanks to the fast-growing rate, easy vegetative propagation and transformation, and availability of genomic ...resources, poplar has been considered the model species for forest genetics, genomics, and breeding. Being a field-growing tree, poplar is exposed to environmental threats, including biotic stresses that are becoming more intense and diffused because of global warming. Current poplar farming is mainly based on monocultures of a few elite clones and the expensive and long-term conventional breeding programmes of perennial tree species cannot face current climate-change challenges. Consequently, new tools and methods are necessary to reduce the limits of traditional breeding related to the long generation time and to discover new sources of resistance. Recent advances in genomics, marker-assisted selection, genomic prediction, and genome editing offer powerful tools to efficiently exploit the Populus genetic diversity and allow enabling molecular breeding to support accurate early selection, increasing the efficiency, and reducing the time and costs of poplar breeding, that, in turn, will improve our capacity to face or prevent the emergence of new diseases or pests.
Salix
L. (willow) is the largest genus of the family Salicaceae and plays an important role in riparian habitats, wetlands and in shrub tundra. Due to the different implications for the species ...belonging to this family, it is fundamental to identify molecular tools characterizing relevant clones. A set of six multilocus and multiallelic simple sequence repeat (SSRs) markers are presented, leading to 390 polymorphic fragments considered as single dominant markers and able to discriminate successfully 92
S. alba
L. from 24
Salix
spp. The polymorphic fragments have been used to perform genetic diversity studies, and to investigate population structures and cluster analysis in a germplasm collection. The results highlight the capability of the six SSRs to be powerful genetic resources in applied forestry research, both to distinguish
S. alba
clones from
Salix
spp. and to perform genetic population studies for breeding programs.
The genus Populus represents one of the most economically important groups of forest trees. It is composed by approximately 30 species used for wood and non-wood products, phytoremediation and ...biomass. Poplar is subjected to several biological and environmental threats although, compared to annual crops, we know far less about the genetic bases of biotic stress resistance. Woolly poplar aphid (Phloeomyzus passerinii) is considered a main pest of cultivated poplars in European and American countries. In this work we present two high density linkage maps in poplar obtained by a genotyping by sequencing (GBS) approach and the identification of QTLs involved in Ph. passerinii resistance. A total of 5,667 polymorphic markers (5,606 SNPs and 61 SSRs) identified on expressed sequences have been used to genotype 131 plants of an F1 population P ×canadensis obtained by an interspecific mate between Populus deltoides (resistant to woolly poplar aphid) and Populus nigra (susceptible to woolly poplar aphid). The two linkage maps, obtained following the two-way pseudo-testcross mapping strategy, have been used to investigate the genetic bases of woolly poplar aphid resistance. One major QTL and two QTLs with minor effects (mapped on LGV, LGXVI and LG XIX) explaining the 65.8% of the genetic variance observed in the progeny in response to Ph. passerinii attack were found. The high density coverage of functional markers allowed the identification of three genes belonging to disease resistance pathway as putative candidates for P. deltoides resistance to woolly poplar aphid. This work is the first report on genetic of woolly poplar aphid genetic resistance and the resistant loci associated markers identified represent a valuable tool in resistance poplar breeding programs.
► Growth and production data on white poplar and willow clones for SRF. ► Selection of new hybrids of white poplar and willow for bioenergy feedstock crops. ► SRC with relative low densities suitable ...for marginal lands.
Although large amounts of residue from agriculture and forestry are presently available for the production of bioenergy, to ensure a sustainable, long-term supply of biomass, it is necessary to establish and grow perennial energy crops on marginal agricultural land that is specifically intended to produce biomass for energy. Preliminary research has identified several perennial crops as potential biofuel crops including perennial grasses, poplars and willows. The high content of cellulose in these species indicates that the materials could be a potential feedstock for bioethanol production too. To select highly productive white poplar and willow clones suitable for these purposes, progenies of Villafranca (Populus alba) and willow clones from different species, mainly Salix matsudana, Salix jessoensis, Salix fragilis and Salix alba, were tested. The preliminary results obtained from plantations set up with 1111 plants per hectare are presented. Higher than the average productivity has been obtained from half-sib progenies of the clone ‘Villafranca’. Among the families obtained with the willow breeding work, including intra-specific hybrids of S. alba, some crosses showed higher growth rates and biomass dry matter yields compared to their parents’ mean values.
Salix L.(willow) is the largest genus of the family Salicaceae and plays an important role in riparian habitats,wetlands and in shrub tundra.Due to the different implications for the species ...belonging to this family,it is fundamental to identify molecular tools characterizing rel-evant clones.A set of six multilocus and multiallelic simple sequence repeat (SSRs) markers are presented,leading to 390 polymorphic fragments considered as single dominant markers and able to discriminate successfully 92 S.alba L.from 24 Salix spp.The polymorphic fragments have been used to perform genetic diversity studies,and to investigate population structures and cluster analysis in a germplasm collection.The results highlight the capability of the six SSRs to be powerful genetic resources in applied forestry research,both to distinguish S.alba clones from Salix spp.and to perform genetic population studies for breeding programs.
► We review theoretical and practical aspects of genetic conservation in forest trees. ► We present pan-European requirements for genetic conservation units of forest trees. ► The requirements ...promote dynamic conservation of genetic diversity. ► The requirements are now used for managing tree populations in 36 countries.
This paper provides a review of theoretical and practical aspects related to genetic management of forest trees. The implementation of international commitments on forest genetic diversity has been slow and partly neglected. Conservation of forest genetic diversity is still riddled with problems, and complexities of national legal and administrative structures. Europe is an example of a complex region where the distribution ranges of tree species extend across large geographical areas with profound environmental differences, and include many countries. Conservation of forest genetic diversity in Europe has been hampered by a lack of common understanding on the management requirements for genetic conservation units of forest trees. The challenge resides in integrating scientific knowledge on conservation genetics into management of tree populations so that recommendations are feasible to implement across different countries. Here, we present pan-European minimum requirements for dynamic conservation units of forest genetic diversity. The units are natural or man-made tree populations which are managed for maintaining evolutionary processes and adaptive potential across generations. Each unit should have a designated status and a management plan, and one or more tree species recognized as target species for genetic conservation. The minimum sizes of the units are set at 500, 50 or 15 reproducing individuals depending on tree species and conservation objectives. Furthermore, silvicultural interventions should be allowed to enhance genetic processes, as needed, and field inventories carried out to monitor regeneration and the population size. These minimum requirements are now used by 36 countries to improve management of forest genetic diversity.
Riparian vegetation supports high biodiversity providing many services and is, therefore, an important landscape element. Riparian ecosystems are subject to numerous pressures leading to population ...decline and genetic erosion of riparian plants. This may have cascading effects at various ecosystem levels, including decreasing ecosystem services, so identifying the current status of genetic diversity of riparian tree species is vital to improve the effectiveness of restoration efforts.
We aimed to elicit expert views on the status and importance of genetic diversity of tree species, and conservation needs across European riparian ecosystems. Sharing of such information among researchers, managers and policymakers has the potential to enhance ecological restoration and management of riparian ecosystems.
We identified experts in riparian genetic resources conservation and management across Europe. These included stakeholders with different perspectives, ranging from researchers to practitioners. We designed a set of questionnaires where our identified experts were asked to answer questions related to the status and conservation of genetic diversity of riparian tree species in their respective countries. Specifically, we asked about societal awareness, legislative tools, good practices and conservation or restoration projects accounting for intraspecific genetic diversity and differentiation of tree species in riparian ecosystems. Questionnaire responses were analysed and discussed in light of the scientific literature to define needs and priorities related to the management and conservation of genetic diversity of riparian tree species.
The experts recognized that a combination of in situ and ex situ measures and/or integrative conservation of riparian ecosystems is the most appropriate option for conserving the genetic diversity of riparian tree species. Simultaneous application of conservation measures at the level of priority species, identified by experts, and protection of riparian areas are required.
Synthesis and applications. This study revealed the importance of recognizing the ecological processes that shape the genetic diversity of riparian tree species in hydrographic networks (dendritic spatial configuration, specific patterns of gene flow among riparian populations, fragmentation of river by dams) but also the need to overcome socio‐economic barriers, such as lack of policy priority, deficiency in funding and weak legislation framework.
This study revealed the importance of recognizing the ecological processes that shape the genetic diversity of riparian tree species in hydrographic networks (dendritic spatial configuration, specific patterns of gene flow among riparian populations, fragmentation of river by dams) but also the need to overcome socio‐economic barriers, such as lack of policy priority, deficiency in funding and weak legislation framework.
Genetically improved forest reproductive materials are now widely accessible in many European countries due to decades of continuous breeding efforts. Tree breeding does not only contribute to ...higher-value end products but allows an increase in the rate of carbon capture and sequestration, helping to mitigate the effects of climate change. The usefulness of breeding programmes depends on (i) the relevance of the set of selected traits and their relative weights (growth, drought tolerance, phenology, etc.); (ii) the explicit management of targeted and “neutral” diversity; (iii) the genetic gain achieved; and (iv) the efficiency of transferring diversity and gain to the plantation. Several biological factors limit both operational breeding and mass reproduction. To fully realise the potential of tree breeding, the introduction of new technologies and concepts is pivotal for overcoming these constraints. We reviewed several European breeding programmes, examining their current status and factors that are likely to influence tree breeding in the coming decades. The synthesis was based on case studies developed for the European Union-funded B4EST project, which focused on eight economically important tree species with breeding histories and intensities ranging from low-input breeding (stone pine, Douglas-fir and ash) to more complex programmes (eucalyptus, maritime pine, Norway spruce, poplar, and Scots pine). Tree breeding for these species is managed in a variety of ways due to differences in species’ biology, breeding objectives, and economic value. Most programmes are managed by governmental institutes with full or partial public support because of the relatively late return on investment. Eucalyptus is the only tree species whose breeding is entirely sponsored and managed by a private company. Several new technologies have emerged for both phenotyping and genotyping. They have the potential to speed up breeding processes and make genetic evaluations more accurate, thereby reducing costs and increasing genetic gains per unit of time. In addition, genotyping has allowed the explicit control of genetic diversity in selected populations with great precision. The continuing advances in tree genomics are expected to revolutionise tree breeding by moving it towards genomic-based selection, a perspective that requires new types of skills that are not always available in the institutions hosting the programmes. We therefore recognise the importance of promoting coordination and collaboration between the many groups involved in breeding. Climate change is expected to bring in new pests and diseases and increase the frequency of extreme weather events such as late frosts and prolonged droughts. Such stresses will cause slow growth and mortality, reducing forest productivity and resilience. Most of these threats are difficult to predict, and the time-consuming nature of conventional breeding does not allow for an adequate and timely reaction. We anticipate that most breeding programmes will need to revise their selection criteria and objectives to place greater emphasis on adaptive performance, tolerance to multiple environmental stresses, stability in different environments, and conservation of genetic diversity. Testing breeding materials in a variety of environments, including potentially contrasting climates, will become increasingly important. Climate change may also force the incorporation of new genetic resources that provide new useful adaptations, which may involve the use of new, previously unexplored gene pools or hybridisation, with the enormous challenge of incorporating useful alleles without adding along an unfavourable genetic background. Decision-support tools to help landowners and foresters select the best-performing forest reproductive material in each specific environment could also help reduce the impact of climate change.
The genus Populus represents one of the most economically important groups of forest trees. It is composed by approximately 30 species used for wood and non-wood products, phytoremediation and ...biomass. Poplar is subjected to several biological and environmental threats although, compared to annual crops, we know far less about the genetic bases of biotic stress resistance. Woolly poplar aphid (Phloeomyzus passerinii) is considered a main pest of cultivated poplars in European and American countries. In this work we present two high density linkage maps in poplar obtained by a genotyping by sequencing (GBS) approach and the identification of QTLs involved in Ph. passerinii resistance. A total of 5,667 polymorphic markers (5,606 SNPs and 61 SSRs) identified on expressed sequences have been used to genotype 131 plants of an F1 population P xcanadensis obtained by an interspecific mate between Populus deltoides (resistant to woolly poplar aphid) and Populus nigra (susceptible to woolly poplar aphid). The two linkage maps, obtained following the two-way pseudo-testcross mapping strategy, have been used to investigate the genetic bases of woolly poplar aphid resistance. One major QTL and two QTLs with minor effects (mapped on LGV, LGXVI and LG XIX) explaining the 65.8% of the genetic variance observed in the progeny in response to Ph. passerinii attack were found. The high density coverage of functional markers allowed the identification of three genes belonging to disease resistance pathway as putative candidates for P. deltoides resistance to woolly poplar aphid. This work is the first report on genetic of woolly poplar aphid genetic resistance and the resistant loci associated markers identified represent a valuable tool in resistance poplar breeding programs.
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