Volume 70 (2021): Edizione 1 (January 2021)

Genetic diversity and the optimal genetic composition are essential for the adaptability and adaptation of tree populations. Artificial regeneration of stands might reduce the genetic diversity and increase family structures if the seeds were collected from a limited number of mother trees. We did a genetic inventory in 12 pedunculate oak stands in Russia using a set of 366 nuclear gene markers (361 SNPs, 5 Indels) in order to look for differences in the genetic composition among natural and artificial stands. Our results did not reveal any systematic differences among both types of stands. However, we found two extreme cases of limited genetic diversity and increased proportion of full-sibs and half-sibs in urban man-made stands. The implications for the forestry and gene conservation programs were discussed.

Provenance trials remain an important tool for understanding genetic variation in forest trees. Maintaining decades-old experiments is critical for revealing maladaptation of translocated populations to local sites and meaningful divergence in survival and growth. We revisited the Second International Larch Provenance Test in southeastern Michigan, which featuring 24 provenances of European and Japanese larch. We compiled data collected when the plantation was 25, 41, and 61 years from seed to supplement data published at 19 years from seed. Divergence in survival rates first became pronounced at 41 years from seed. Plantation sources of unknown origin and continental Sudeten provenances had the highest rates of survival. High-elevation sources from the southern Alps performed the poorest. Survival differences were likely driven by ice storm damage and severe growing season droughts, both of which occurred at least 1-2 times per decade in southeastern Michigan over the last 60 years. Provenance performance for growth mirrored that of survival, although sources varied more in their survival than in their growth. Growth rate among sources varied over the 43-year sampling period, with intervals of fast growth occurring in several of the overall poor-performing provenances. Diameter was moderately correlated to both elevation and latitude, with inconsistent correlations to climatic variables. Broad geographical variation in provenance performance was also important in explaining variation in growth. Our data corroborate that monitoring of long-term provenance trials could be an important source of information needed to predict and understand how forest species may respond to imminent climate change and may be critical for developing strategies for its mitigation.

Recent polyploidy in gymnosperms is unusually scarce being present in only 9.80 % of the 714 taxa studied cytologically. Polyploid forms are represented by sporadic seedlings and individual trees, intraspecific polyploidy in cultivation or in wild and entirely polyploid species and genera. Polyploidy shows a non-random distribution in different genera being mostly prevalent in Ephedra and Juniperus, besides the classic examples of Sequoia and Fitzroya. Remarkably, both Ephedra and Juniperus show adaptive radiation by interspecific hybridization followed by polyploidy while in Ginkgo viable polyploid cytotypes are found in cultivation. Induced polyploidy has not provided any tangible results in the past but recent attempts on certain genera of Cupressaceae hold some promise of producing cultivars for horticulture trade. Lastly, various evidences derived from cytological analysis, fossil pollen, guard cells and comparative genomic studies indicating the occurrence of paleopolyploidy have been discussed.

The Natural Resources Research Institute Hybrid Poplar Program breeds and tests genetically improved clones for bio-mass production and environmental services. The testing process progresses from Nursery Progeny Tests (NPT) to Family Field Trials (FFT) to Clone Trials (CT) to Yield Blocks (YB), with limited replication of many clones in FFT and CT and a limited number of highly selected clones set out in monoclonal blocks (YB) to approximate the conditions of commercial plantations. We used correlation vectors, R² (coefficient of determination) and r_s (Spearman’s Coefficient) for growth (DBH²) and McFadden’s Pseudo R² for canker severity score, to determine where testing times could be altered (age – age correlations) and whole testing steps eliminated. FFT can be shortened from 5 years to 4 years. In CT, rank correlations between age 5 (half-rotation) and age 9/10 (full rotation) were significant (R² = 0.39 – 0.72), but age 5 selection missed 44 % of the top ten clones at age 9/10. Clone rank in CT at full, but not half, rotation was correlated with rank at full rotation in YB. Choosing clones at 9 years in CT adds 4 years but allows possible elimination of YB for clone selection. Both FFT and CT are necessary. Canker abundance and severity in CT at full rotation cannot be determined at earlier ages. An aggressive strategy saves 6 years of testing.

Plant SABATH family members catalyze the methylation of many hormones, signaling molecules, and floral scent metabolites, including salicylic acid (SA), jasmonic acid (JA), and indol-3 acetic acid (IAA). Demethylation of resulting methyl esters was executed by members of the MES family. Members of both families are significantly involved in plant developmental processes. Here, using different bioinformatics tools, we studied the evolutionary relationship and characterized the putative functions of the family members in silver birch (Betula pendula). It is a socio-ecologically important tree species and plays a vital role in reforestation. Ten and twelve members of the SABATH (BpSABATH1-10) and MES (BpMES1-12) family were identified in silver birch, respectively at the gene and enzyme levels. The BpSABATH and BpMES genes were distributed on seven of fourteen chromosomes, indicating the occurrence of moderate duplication events important for the expansion of both families. Phylogenetic clustering and the gene ontology database suggest, BpSA-BATH8 is involved in the methylation of indole-3-acetic acid (IAA), while BpSABATH5, BpSABATH6, and BpSABATH7 methylate JA to methyl jasmonate (MeJA). BpSABATH9 was alone in the phylogenetic functional group 1 and prefers SA as a substrate to synthesize methyl salicylate (MeSA). Likewise, BpMES5 and BpMES12 are possibly involved in the demethylation of the methyl ester of IAA, while BpMES6, BpMES7, and BpMES8 are responsible for the demethylation of MeJA. BpMES9 clustered with MES and prefers MeSA as a substrate. The current analysis helped to select candidate genes that could be subjected to further molecular breeding of birch varieties adapted to biotic and abiotic stress conditions.

Salix is a genus of considerable taxonomic complexity, and accurate identification of its species and hybrids is not always possible. Quantification of ovules was used in this study to verify the parentage of a few hybrids of Salix. It has been shown that ovule numbers in willow hybrids are the mean of the ovule numbers of their parents. The ovule index of a prostrate specimen of S. ×cottetii affirmed that this was a hybrid of S. myrsinifolia Salisb. and S. retusa L., and the ovule index of the ornamental cultivar ‘The Hague’ affirmed that this was a hybrid of S. caprea L. and S. gracilistyla Miq. Finally, we also examined a confusing group, previously identified in North America as S. pentandra. The ovule indexes and other morphological characters indicated that there were four taxa among the studied specimens: S. pentandra, S. ×meyeriana, S. serissima Fernald, and a hybrid of S. serissima and S. fragilis that has not previously been described. It was concluded that quantification of ovules in willows is a reliable tool that can be used in willow taxonomy, genetics and population studies.

New first and 1.5 generation seed orchards are to be created in Germany based on recently assembled breeding populations of Acer pseudoplatanus, Larix sp., Picea abies, Pinus sylvestris, Pseudotsuga menziesii, and Quercus sp. To justify the high expenses in time and cost for orchard establishment and maintenance, planning should make use of consolidated knowledge and experience of both the national and international scientific community. Here, we briefly describe advances in genetic gains achieved through tree breeding, and resume population genetic aspects and design considerations to draw conclusions for clonal composition and spatial design of the new orchards.

We conclude that to avoid outbreeding depression separate orchards are required for each breeding zone. The zones are species-specific and defined by ecological and climatic aspects. A minimum of 60-80 clones per orchard is recommended for native tree species with high proportions of natural regeneration in forest practice. This would allow future selective thinning based on estimated breeding values from progeny testing. It would also permit the transfer of seed orchard progenies into a naturally regenerating forest stands without the risk of a genetic bottleneck. Lower clone numbers are appropriate for non-native species and hybrids. It is important to strictly avoid inbreeding depression, achieved by using only one clone per progeny or population, from which the plus trees were selected. Further, the spatial layout should promote random mating by optimizing the neighbourhood of each clone. With all of these considerations taken into account, we expect superior quality traits and at least 10-15 % more volume from the new seed orchards.

The total of 257 trees from the ten natural Siberian stone pine populations of West Siberian Plain, Ural Mountains and Kuznetsk Alatau were studied with the eight nuclear microsatellite loci. Differentiation of population groups indicates the possible existence of separate refugia in the past in the Urals and Kuznetsk Alatau. The northern populations of Western Siberia were characterized by a reduced level of genetic diversity, which could be a consequence of the founder effect in the process of P. sibirica migration from the southern regions of Western Siberia and the Urals since the end of the last glacial maximum. The genetic variability distribution among populations shows the uneven dynamics of Siberian stone pine migration from the zones of supposed refugia. The map of the proposed ways of Siberian stone pine migration from the zones of possible refugia was constructed, and it is in a good agreement with the results of palynological investigations.

Cross-amplification is a cost-effective method to extend the applicability of SSR markers to closely related taxa which lack their own sequence information. In the present study, 35 SSR markers developed in four oak species of Europe, North America and Asia were selected and screened in five species of the western Himalayas. Fifteen markers were successfully amplified in Quercus semecarpifolia, followed by 11 each in Q. floribunda and Q. leucotrichophora, 10 in Q. glauca, and 9 in Q. lana-ta. Except two primer pairs in Q. semecarpifolia, all were found to be polymorphic. Most of the positively cross-amplified SSRs were derived from the Asian oak, Q. mongolica. The genoty-ping of 10 individuals of each species with positively cross-amplified SSRs displayed varied levels of polymorphism in the five target oak species, viz., QmC00419 was most polymorphic in Q. floribunda, QmC00716 in Q. glauca and Q. lanata, QmC01368 in Q. leucotrichophora, and QmC02269 in Q. semecarpifolia. Among five oak species, the highest gene diversity was depicted in Q. lanata and Q. semecarpifolia with expected heterozygosity (He = 0.72), while the minimum was recorded for Q. leucotrichophora and Q. glauca (He = 0.65). The SSRs validated here provide a valuable resource to carry out further population genetic analysis in oaks of the western Himalayas.

Woody plants have been cultured in vitro since the 1930s. After that time much progress has been made in the culture of tissues, organs, cells, and protoplasts in tree species. Tree biotechnology has been making strides in clonal propagation by organogenesis and somatic embryogenesis. These regeneration studies have paved the way for gene transfer in forest trees. Transgenics from a number of forest tree species carrying a variety of recombinant genes that code for herbicide tolerance, pest resistance, lignin modification, increased woody bio-mass, and flowering control have been produced by Agrobacterium-mediated and biolistic methods, and some of them are undergoing confined field trials. Although relatively stable transgenic clones have been produced by genetic transformation in trees using organogenesis or somatic embryogenesis, there were also unintended unstable genetic events. In order to overcome the problems of randomness of transgene integration and instability reported in Agrobacterium-mediated or biolistically transformed plants, site-specific transgene insertion strategies involving clustered regularly interspaced short palindromic repeats (CRISPR-Cas9) platform offer prospects for precise genome editing in plants. Nevertheless, it is important to monitor phenotypic and genetic stability of clonal material, not just under greenhouse conditions, but also under natural field conditions. Genetically modified poplars have been commercialized in China, and eucalypts and loblolly pine are expected to be released for commercial deployment in USA. Clonal forestry and transgenic forestry have to cope with rapid global climate changes in the future. Climate change is impacting species distributions and is a significant threat to biodiversity. Therefore, it is important to deploy Strategies that will assist the survival and evolution of forest tree species facing rapid climate change. Assisted migration (managed relocation) and biotechnological approaches offer prospects for adaptation of forest trees to climate change.

We investigated the clonal structure, self-incompatibility, and number of seeds per fruit in Camellia rusticana, a Japanese endemic species, in comparison to the closely related C. japonica. Clonal propagation was more vigorous in C. rusticana than in C. japonica and the clonal structure of C. rusticana varied among populations. C. rusticana can maintain genets for extended periods, even in harsh environments such as high-altitude areas with considerable snow accumulation, because even a single surviving genet can propagate clonally. However, sexual reproduction (i.e., reproduction by seed) is advantageous for dispersal to distant suitable habitats. An artificial crossing test revealed high self-incompatibility in C. rusticana, as observed in C. japonica. In addition, the number of seeds per fruit was lower in C. rusticana than in C. japonica. Self-incompatibility in C. rusticana may play a role in production of high-quality seed, despite low seed production.

Many dioecious angiosperms are trees, which only flower after years of vegetative development and do not usually exhibit marked secondary sexual dimorphism. Nevertheless, if the genetic basis of sex determination is known, the sex of an individual can be determined using molecular markers. Here, we report that in the genus Populus sect. Populus an XY system of sex determination, which is found in P. tremula and P. tremuloides, likely re-evolved from a ZW system present in P. alba, P. adenopoda and P. qiongdaoensis. Strikingly, this new XY system is mechanistically identical to the older system found in several species of the Populus sections Tacamahaca, Aigeiros and Turanga demonstrating a remarkable example of convergent evolution. In both XY systems, male-specific inversely repeated sequences appear to silence the ARR17 gene, which functions as a sex switch, via small interfering RNAs and DNA methylation. In the ZW system, female-specific copies of ARR17 appear to regulate dioecy. With this detailed information on the genetic basis of sex determination it was possible to develop molecular markers that can be utilized to determine the sex in seedlings and non-flowering trees of different poplar species. We used the female-specific ARR17 gene to develop a sex marker for P. alba and P. adenopoda. For P. grandidentata, we employed the male-specific ARR17 inverted repeat. Finally, we summarize previously described markers for P. tremula, P. tremuloides, P. trichocarpa, P. deltoides and P. nigra. These markers can be useful for poplar ecologists, geneticists and breeders.

Gymnosperms show a significantly higher mean (1C=18.16, 1Cx=16.80) and a narrow range (16.89-fold) of genome sizes as compared with angiosperms. Among the 12 families the largest ranges of 1C values is shown by Ephedraceae (4.73-fold) and Cupressaceae (4.45-fold) which are partly due to polyploidy as 1Cx values vary 2.41 and 1.37-fold respectively. In rest of the families which have only diploid taxa the range of 1C values is from 1.18-fold (Cycadaeae) to 4.36-fold (Podocarpaceae). The question is how gymnosperms acquired such big genome sizes despite the rarity of recent instances of polyploidy. A general survey of different families and genera shows that gymnosperms have experienced both increase and decrease in their genome size during evolution. Various genomic components which have accounted for these large genomes have been discussed. The major contributors are the transposable elements particularly LTR-retrotransposons comprising of Ty3gypsy, Ty1copia and gymny superfamilies which are most widespread. The genomes of gymnosperms have been acquiring diverse LTR-RTs in their long evolution in the absence of any efficient mechanism of their elimination. The epigenetic machinery which silences these large tracts of repeat sequences into the stretches of heterochromatin and the adaptive value of these silenced repeat sequences need further investigation.

The equatorial region of the world includes areas of Tropical Rainforest (Af) and Tropical Monsoon (Am) climate zones, which are distinguished by high temperatures and high rainfall, but soils which are often deficient. Potential productivity of plantation forestry in this area is high, and so are the pest and disease dangers which threaten it. This paper describes the Eucalyptus and Corymbia species which are adapted to this situation and also resistant to the main diseases like leaf blights. Based on the highly adapted E. biterranea and E. deglupta and several more, hybridization combined with vegetative propagation is discussed as an excellent alternative to obtain quick gains in short rotations while maintaining wide genetic diversity in such plantations. Management remedies are given for the possible backlash of quick soil depletion.

Pine wilt disease is one of the most serious tree diseases occurring worldwide. Clones of Pinus densiflora Siebold et Zucc with pine wood nematode resistance were selected. In addition to resistance, wood quality is also an important criterion in the breeding program of P. densiflora because of its use as construction lumber. However, little information is available on the wood qualities of the progenies of resistant clones. The repeatabilities of the wood properties were investigated for 11 open-pollinated families of P. densiflora selected for their pine wood nematode resistance. Oven-dry density, latewood tracheid length, the microfibril angle (MFA) of the S2 layer in latewood tracheids, modulus of elasticity (MOE), and modulus of rupture (MOR) were measured in the third or fourth annual ring from the pith. No significant correlations were found between the wood properties and the stem diameter or tree height. However, significant correlations were found between oven-dry density and MOE or MOR, which suggests that oven-dry density is a good indicator for selecting wood with higher bending properties. Among the measured wood properties, oven-dry density had the highest repeatability (R=0.47), followed by MOR (R=0.33), tracheid length (R=0.21), and MFA (R=0.14). MOE had the lowest value (R=0.01). The 11 families examined were classified into three groups according to their growth characteristics, wood properties, and resistance to pine wilt disease. On the basis of the results, we conclude that genetic improvement of wood properties especially for wood density and MOR is possible for the resistant P. densiflora.

Gmelina arborea is the second most planted tree species in Costa Rica, and one of the most important in several Latin American countries. In recent years, a disease caused by Ceratocystis fimbriata, has spread throughout Latin America, leading to the complete root of the tree in a few months. This study was conducted to evaluate the incidence, severity and genetic tolerance control of the Ceratocystis wilt in G. arborea. Data is based on a 2.4-year-old clonal trial, with 34 elite genotypes, at Río Jiménez, Guácimo in the Costa Rican Caribbean region. The variables diameter at breast height (DBH), total height, disease incidence and disease severity were evaluated. A pathogenicity index was proposed as a new selection criterion. SELEGEN (EMBRAPA) software was used for the evaluation of the genetic control in all traits investigated. Overall incidence rate was 39 % and severity was 13 %. Mean clonal heritability for severity was h²mc= 0.59 and for incidence h²mc= 0.47, these values were high evidencing that both traits are under a strong genetic control. The pathogenicity index becomes a useful discrimination criterion for ranking genotypes by their disease tolerance. An infection pattern inversely proportional to the DBH was observed. Although none of the 34 genotypes evaluated recorded total resistance to C. fimbriata, eight of these genotypes show strong genetic tolerance to the disease, and high productivity. Their use can be encouraging and will contribute to the reduction of Ceratocystis wilt impact in the country, as well as in the tropical Latin America region.

Pinus koraiensis Sieb. et Zucc. (Korean pine) is an evergreen coniferous tree species with significant therapeutic and nutritional value in northeastern China. To assess variation and select highly productive and nutritionally valuable materials, 25 cone, seed, and kernel nutritional components traits were measured and analyzed. Coefficients of variation for phenotypic traits ranged from 6.32 % to 161.51 %, and the coefficients of most traits were approximately 10 %. Most traits showed significant or extremely significant differences among clones or groups, especially for amino acid content. Cone numbers were under moderate genetic control, and their repeated ability ranged from 0.42 to 0.53. Most other traits were under high genetic control, and their repeated ability was higher than 0.70. Despite the weak correlation with seed traits, cone number had strong correlations with other characters. Four principal components were obtained with a cumulative variance contribution of 93.51 %. The selected elite material will provide a theoretical basis for selection and breeding of P. koraiensis.

The improvement of Eucalyptus clones plays a crucial role in modern silviculture. This study used a set of 17 microsatellite loci to analyze the genetic diversity and structure of 107 elite clones (80 E. grandis and 27 E. globulus). All clones were cultivated in Uruguay and were sourced from three different providers. Using the fingerprinting technique, an exclusive molecular profile was assigned for each clone, and the genotyping reaction showed differences between the two species. The cumulative probability of identifying two random individuals that share the same genotype (PI) with all 17 loci, was estimated as low for E. grandis (1.18×10-15) and E. globulus (4.03×10-14). The combined PIsibs was (1.05×10-5) and (2.17×10-5) for E. grandis and E. globulus, respectively. A total of 180 alleles were detected for E. grandis and 100 for E. globulus. We found a high mean number of alleles per locus (10 for E. grandis and 6 for E. globulus), and the results for mean polymorphic information content (PIC ) were (0.648) and (0.548), respectively. The observed heterozygosity (H_o) ranged from 0.216 to 0.838 (mean = 0.509) for E. grandis and 0 to 1 (mean = 0.566) for E. globulus. Two core sets of seven EST-SSR loci were identified for each species. These markers revealed unambiguous fragment amplification, providing a minimum number of SSRs for effective clonal identification. The genetic structure analysis suggests that the germplasm of the E. grandis population is structured in four clusters, while the E. globulus population consists of two clusters.

Pedunculate oak (Quercus robur L.) is one of the most significant broadleaved tree species in Europe. However, various abiotic and biotic agents have influenced pedunculate oak forests, among which drought stress has been frequently described as the main driver of this species forests decline. In this study we assessed relative expression profile of 11 candidate genes involved in many different metabolic pathways and potentially responsible for oak drought tolerance. The obtained results succeed in partially tackling drought tolerance mechanisms of targeted natural pedunculated oak population. This gene pool may represent a base for adaptation and therefore genetic diversity should be conserved. In this paper we described different expression responses of four pedunculate oak ecological groups, characterized by different physiological status (senescent vs vital) and flowering period (early (var. praecox) vs late (var. tardissima)). The most significant differences in relative gene expression levels are shown between the flowering period (tardissima (8 genes upregulated) vs praecox (3 genes upregulated)), more than a physiological status (sene-scent vs vital). Only three genes wrky53, rd22 and sag21 showed upregulated expression pattern in senescent physiological groups, indicating their possible role in the coping mechanisms of oak in stressed environment. Results showed interesting connections of relative gene expression values of identified drought-tolerance related genes with flowering period and provide further recommendations for adequate conservation and monitoring of this important oak gene pool in its southeast refugium.