Development of 5S rDNA-Based Molecular Markers for the Identification of Populus deltoides Bartr. ex Marshall, Populus nigra L., and Their Hybrids

Populus L. is a tree genus that includes species with a high ability for interspecies hybridization. This process takes place in nature, and is used in poplar breeding. As а result, species identification in poplar populations and plantations is very difficult. In this study, a molecular marker system was developed for the identification of the most significant poplar species (P. nigra L. and P. deltoids Bartr. ex Marshall). The basis of the system is a polymorphism in non-transcribed spacers (NTSs) of 5S rDNA. The species-specific molecular markers were tested on a number of species and hybrids of poplars. It was shown that the marker system is a powerful tool for species identification, hybrid analysis, parent identification, and poplar breeding.

Microsatellite Diversity of Androgenic Black Poplar (Populus nigra)

Genetic variation of somatic clones (1 to 35) of black poplar (Populus nigra) developed from two anther-donor trees N-SL and N-309 was determined by five SSR primer pairs. Twenty SSR alleles were detected, the number of alleles per marker ranged from 1 to 6, with an average of 3.3 including WPMS-2 (5 alleles), WPMS-4 (6 alleles), WPMS-6 (2 alleles), WPMS-20 (6 alleles) and PTR-4 (1 allele) detected by ALF (automatic laser fluorometer). Adendrogram produced by SPSS11 based on the presence versus absence of SSR alleles discriminated the groups of somatic clones of N-SL from somatic clones of N-309. The polymorphic markers of WPMS-2 (5 alleles), WPMS-4 (6 alleles) and WPMS-20 (6 alleles) revealed clonal variation in 1 clone (37) out of the 6 from the N-309 tree, and three subgroups out of the 29 somatic clones from the N-SL tree (17 and 24), (2 and 14) and (10 and 15). The remaining 23 of the 29 N-SL somatic clones with uniform genetic similarity suggests a good degree of genetic stability in black poplar. Nevertheless, the new SSR-clones may provide useful new genetic resources for poplar breeding.

Diversity and breeding potential of poplar species in China

The genus Populus is composed of many species with an impressive variety of growth characteristics. Nevertheless, this abundant natural offering has been only partially utilized to date with the objective of promoting poplar breeding and cultivation. Following an old tradition, more or less inflexible production systems are mainly keyed to a few high-yielding P. x euramericana and P. x interamericana clones in most countries. Consequently, considerable economic failures have to be accepted repeatedly as a result of serious calamities.China ranks among the countries characterized by an exceptionally multifarious indigenous flora. Based on ample genetic variation, poplar species were able to settle in divergent habitats and to conserve the ability to survive and reproduce over long periods owing to adaptation processes. The diversity is concentrated, above all, in the subtropical mountain regions of southwest China. Comprehensive studies of the genus populus in the southern and eastern mountain chains of the Qinghai-Tibet Plateau turned out to be particularly impressive; 3 sections, 17 species and 15 varieties have been recorded and taxonomically classified there. They grow at altitudes between 1500 m and 4300 m above sea level. Many of these poplar sources are notable for their remarkable site adaptation even in harsh conditions and also for their fast and vigorous growth.Species expected to be suitable for international breeding and cultivation objectives in the near future are presented in a general way. The necessarily subjective selection is based on the state of available knowledge mainly about site requirements, environmental importance, growth characteristics, regeneration ability, silvicultural behaviour, yield estimation and wood utilization. In particular, the following species are characterized in the paper in an abridged fashion: P. cathayana, P. davidiana, P. euthratica, P. simonii, P. szechuanica, P. ussuriensis and P. yunnanensis.The potential of poplars in China is considered to be instrumental in expanding and stimulating poplar breeding activities worldwide. Measures to be specified in the paper are considered important and could be implemented on the basis of a close and confident co-operation with Chinese colleagues and institutes relevant to the subject and under the umbrella of the International Poplar Commission. Key words: poplar, tradition, calamities, China, genetic variation, promising species, characteristics, breeding priorities

Poplar breeding for the purpose of biomass production in short rotation periods in Germany: Problems and first findings

Investigations so far on the suitability of poplars for biomass production in short rotation periods in Germany were conducted almost exclusively with clones conceived for conventional cultivation. To introduce improved plant material, a special breeding program was implemented in Hann. Münden. It takes into consideration the most important criteria of suitability for the new form of land utilization. A report is given on findings so far from the realization of this program. Comprehensive basic plant material is available for European, North American and East Asian species from the sections Aigeiros, Leuce and Tacamahaca. Interspecific crossings are being carried out mainly in order to make the best possible use of combination and heterosis effects. A period of at least 20 years is necessary to develop new cultivars with high yield performance and yield stability. First results are presented on hybrids of species which are site-tolerant, resistant and particularly fast-growing at the juvenile phase. Plans to produce multiclonal varieties, each with 5 to 10 suitable clones with the same growing rhythm are in place. Special cultivation recommendations advocate clonal mixtures for each of the most important site units and for different rotation periods of from 2 to 5, 6 to 10 and more than 10 years. Key words: poplar, breeding, biomass, short rotation

Future possibilities for poplar breeding

Poplar breeding should concentrate on studies of the inheritance of characteristics, using suitable mating designs. Estimates of genetic parameters will allow genetic gain predictions which will better indicate the potential of poplar breeding and help in choosing appropriate breeding methods. Sexual propagation should be given more attention for producing varieties than commonly practiced. Special stress should be placed on provenance studies in pure species. It seems desirable to place more emphasis on selection of wood properties.