Analysis of the influence of particle and poplar fibres share on selected properties of particle-fibre boards

Analysis of the influence of particle and poplar fibres share on selected properties of particle-fibre boards. As a part of the study, one-layer particle-fibre boards with 12 mm thick and of average density 650 kg/m3 were manufactured from plantation poplar ‘Hybrid 275’ wood.. For the control variant a typical industrial raw material (pine wood) was used. The following properties were determined for the boards: modulus of rapture (MOR), density profile, modulus of elasticity at static bending (MOE), internal bond (IB), thickness swelling (TS) after 2h and 24h soaking in water. On the basis of conducted study, it was found that the addition of poplar fibers to particle-fibre boards in most cases has a positive effect on the values of determined properties – an increase in strength was noted, except for internal bond (IB). In the case of thickness swelling of the boards after 24 h soaking in water, it was noted that with the increase in the share of poplar fibers in the boards, the value of the tested property decreased (which was not clear in the case of thickness swelling of boards after 2 h soaking in water).

The genome of Populus alba x Populus tremula var. glandulosa clone 84K

Poplar 84K (Populus alba x P. tremula var. glandulosa) is a fast-growing poplar hybrid. Originated in South Korea, this hybrid has been extensively cultivated in northern China. Due to the economic and ecological importance of this hybrid and high transformability, we now report the de novo sequencing and assembly of a male individual of poplar 84K using PacBio and Hi-C technologies. The final reference nuclear genome (747.5 Mb) has a contig N50 size of 1.99 Mb and a scaffold N50 size of 19.6 Mb. Complete chloroplast and mitochondrial genomes were also assembled from the sequencing data. Based on similarities to the genomes of P. alba var. pyramidalis and P. tremula, we were able to identify two subgenomes, representing 356 Mb from P. alba (subgenome A) and 354 Mb from P. tremula var. glandulosa (subgenome G). The phased assembly allowed us to detect the transcriptional bias between the two subgenomes, and we found that the subgenome from P. tremula displayed dominant expression in both 84K and another widely used hybrid, P. tremula x P. alba. This high-quality poplar 84K genome will be a valuable resource for poplar breeding and for molecular biology studies.

Evaluating the Efficiency of gRNAs in CRISPR/Cas9 Mediated Genome Editing in Poplars

CRISPR/Cas9 has become one of the most promising techniques for genome editing in plants and works very well in poplars with an Agrobacterium-mediated transformation system. We selected twelve genes, including SOC1, FUL, and their paralogous genes, four NFP-like genes and TOZ19 for three different research topics. The gRNAs were designed for editing, and, together with a constitutively expressed Cas9 nuclease, transferred either into the poplar hybrid Populus × canescens or into P. tremula. The regenerated lines showed different types of editing and revealed several homozygous editing events which are of special interest in perennial species because of limited back-cross ability. Through a time series, we could show that despite the constitutive expression of the Cas9 nuclease, no secondary editing of the target region occurred. Thus, constitutive Cas9 expression does not seem to pose any risk to additional editing events. Based on various criteria, we obtained evidence for a relationship between the structure of gRNA and the efficiency of gene editing. In particular, the GC content, purine residues in the gRNA end, and the free accessibility of the seed region seemed to be highly important for genome editing in poplars. Based on our findings on nine different poplar genes, efficient gRNAs can be designed for future efficient editing applications in poplars.

Inducing genetic variation in growth related characteristics of poplar germplasm, by producing inter-specific hybrids between P. alba and P. euphratica

Crosses were made between two Populus species to create two hybrid groups, P. alba ♀ * P. euphratica ♂ and P. euphratica ♀ * P. alba ♂. Aseptic immature hybrid seeds were first grown on MS medium. Hybrid seedlings were then acclimatized and grown in greenhouse conditions and transplanted to an experimental field. Growth related characteristics were recorded on 307 three years-old seedlings of new inter-specific hybrids of six half-sib families, in order to assess possible potentials of the two hybrid groups. Double nested analysis of variance revealed significant differences between the hybrid groups and siblings based on majority of the studied characters. The hybrid groups formed two distinct groups for some of the studied characteristics which implied maternal effects of inheritance on the traits. The first hybrid group had more but shorter and closer branches than the second group. Adaxial stomata number for the two hybrid groups varied between 4.7 to 123. Whereas, there were no such strong differences between vegetative characteristics of the two groups. The second hybrid group had a very condense layer of white fuzz on its abaxial leaf surface, inherited from its female parents. This may lead to suggest some kinds of photosynthesis and respiration functions such as leaf sub-stomatal chambers’ functions for the mentioned fuzzy trichomes of the second hybrid group and their female parental species, P. alba. In essence, 307 new divergent poplar hybrid genotypes were produced by which ecological zone of poplar species could be extended in the country as well as high yielding genotypes would be promising.