Search Results (7)

The identification of genotypes more tolerant to water deficit is a challenge to breeding programs. In this research, our objectives were to identify and validate traits for tolerance to water deficit in eucalypts. The estimation of genotypic parameters and early selection are proposed based on mixed models, selection indexes and validation schemes. Seedlings with 110 days were grown in a greenhouse for 12 weeks, and two water deficit treatments were conducted (polyethylene glycol and water limitation). A total of 26 biomarkers were evaluated, and 15 of them were significant, exhibited adequate heritability, and used for screening: final plant height, increment in height, increment in diameter, area of mature and fully expanded leaf, nutrient contents of N, K, Ca, Mg, S, Cu, Zn, Mn and B, photosynthesis (A) and stomatal conductance (gs). Both treatments were adequate to discriminate water deficit-tolerant clones. The ranking of tolerant clones according to their phenotype in the field demonstrates the potential for early selection and is consistent with the maintenance of water-deficit-tolerance mechanisms until adulthood. There is evidence that the choice of biomarker depends on the species involved and different strategies contributing to the tolerance trait. Full article

The quantitative, accurate and efficient acquisition of tree phenotypes is the basis for forest “gene-phenotype-environment” studies. It also offers significant support for clarifying the genetic control mechanisms of tree traits. The application of unmanned aerial vehicle (UAV) remote sensing technology to the collection of phenotypic traits at an individual tree level quantitatively analyses tree phenology and directionally evaluates tree growth, as well as accelerating the process of forest genetics and breeding. In this study, with the help of high-resolution, high-overlap, multispectral images obtained by an UAV, combined with digital elevation models (DEMs) extracted from point clouds acquired by a backpack LiDAR, a high-throughput tree structure and spectral phenotypic traits extraction and a genetic selection were conducted in a trial of Eucalyptus clones in the State-owned Dongmen Forest Farm in the Guangxi Zhuang Autonomous Region. Firstly, we validated the accuracy of extracting the phenotypic parameters of individual tree growth based on aerial stereo photogrammetry point clouds. Secondly, on this basis, the repeatability of the tree growth traits and vegetation indices (VIs), the genetic correlation coefficients between the traits were calculated. Finally, the eucalypt clones were ranked by integrating a selection index of traits, and the superior genotypes were selected and their genetic gain predicted. The results showed a high accuracy of the tree height (H) extracted from the digital aerial photogrammetry (DAP) point cloud based on UAV images (R² = 0.91, and RMSE = 0.56 m), and the accuracy of estimating the diameter at breast height (DBH) was R² = 0.71, and RMSE = 0.75 cm. All the extracted traits were significantly different within the tree species and among the clones. Except for the crown width (CW), the clonal repeatability ($R_c)$ of the traits were all above 0.9, and the individual repeatability values ($R_i)$ were all above 0.5. The genetic correlation coefficient between the tree growth traits and VIs fluctuated from 0.3 to 0.5, while the best clones were EA14-15, EA14-09, EC184, and EC183 when the selection proportion was 10%. The purpose of this study was to construct a technical framework for phenotypic traits extraction and genetic analysis of trees based on unmanned aerial stereo photography point clouds and high-resolution multispectral images, while also exploring the application potential of this approach in the selective breeding of eucalypt clones. Full article

Novel genetic accessions of Eucalyptus polybractea from a previously untested, hotter and drier part of the species’ natural range were tested in a common garden trial at a semi-arid site in NSW, Australia. Eucalyptus polybractea is a mallee eucalypt cultivated for essential oils (1,8-cineole), bioenergy and carbon sequestration on dryland sites in southern Australia (sites receiving about 450 mm mean annual rainfall, MAR). A trial of six previously untested provenances from the relatively hot, dry part of the species’ natural range in South Australia (SA) (250–450 mm MAR) was established alongside seven provenances from New South Wales (NSW) and Victoria within a commercial plantation in NSW. The trial was assessed at age 3.7 years for growth and oil characteristics. While survival was excellent, most of the SA sources were slower growing and of sub-standard oil concentration and quality relative to those from Victoria and NSW. However, a single SA provenance, with the highest oil concentration and 1,8-cineole percentage of all provenances tested, may have potential as a source of selected germplasm. Infusion of SA material into the breeding populations of E. polybractea, which are currently based on NSW and Victorian selections only, may provide more resilience in the face of hotter and drier temperatures expected under projected climate change scenarios, and/or allow the introduction of the species to hotter and drier climates in Australia or other parts of the world with semi-arid climates. However, high-intensity selection of infusions will be required to maintain the growth and oil characteristics in the existing breeding population. Full article

Eucalyptus globulus (Labill.) is one of the most important cultivated eucalypts in temperate and subtropical regions and has been successfully subjected to intensive breeding. In this study, Bayesian genomic models that include the effects of haplotype and single nucleotide polymorphisms (SNP) were assessed to predict quantitative traits related to wood quality and tree growth in a 6-year-old breeding population. To this end, the following markers were considered: (a) ~14 K SNP markers (SNP), (b) ~3 K haplotypes (HAP), and (c) haplotypes and SNPs that were not assigned to a haplotype (HAP-SNP). Predictive ability values (PA) were dependent on the genomic prediction models and markers. On average, Bayesian ridge regression (BRR) and Bayes C had the highest PA for the majority of traits. Notably, genomic models that included the haplotype effect (either HAP or HAP-SNP) significantly increased the PA of low-heritability traits. For instance, BRR based on HAP had the highest PA (0.58) for stem straightness. Consistently, the heritability estimates from genomic models were higher than the pedigree-based estimates for these traits. The results provide additional perspectives for the implementation of genomic selection in Eucalyptus breeding programs, which could be especially beneficial for improving traits with low heritability. Full article

Triploids generally provide an advantage in vegetative growth in forest trees. However, the technique of triploid breeding is still an open field in the Eucalyptus tree species. This study aims to explore the colchicine treatment technique for megaspore chromosome doubling to establish triploids in this tree species. Cytological observation on microsporogenesis and megasporogenesis was carried out to guide megaspore chromosome doubling induced by colchicine treatment. Ploidy level in progenies was detected by flow cytometry and somatic chromosome counting. A relationship between microsporogenesis and megasporogenesis was established to guide the colchicine treatment. Seven triploids were obtained in the progenies, and the highest efficiency of triploid production was 6.25% when the flower buds underwent a 0.25% colchicine solution treatment for 6 h using an aspiration method seven days after the first observation of leptotene during microsporogenesis on the floral branch. Cytological analysis showed that the megasporocyte from leptotene to diakinesis may be the optimal period for megaspore chromosome doubling by colchicine treatment. Plant height, ground diameter, leaf area, and the photosynthetic parameter of triploid eucalypt were significantly higher than those of the diploid plant at 6 months old. Hybridization with 2n megaspores induced by colchicine treatment is an effective way for Eucalyptus triploid breeding. These results should accelerate the development of advanced germplasms in this tree species. Full article

Forest tree hybrid zones provide a wealth of novel genetic variation that can be harnessed to safeguard populations in changing climates. In the past 30 years, natural and artificial forest hybrid zones have facilitated significant contributions to selective breeding programs, conservation, and our understanding of the evolutionary processes and mechanisms that influence the maintenance of species and community interactions. This review highlights advances in these areas using forest hybrid zones. Taking examples from well-known genera, including eucalypt, poplar, oak and spruce, this review details the important role hybrid zones play in managing conservation of genetic variation, the environmental and non-environmental factors that influence barriers to reproduction, and the impact that genetic ancestry may have on community biodiversity. Given increasing concern surrounding species adaptability under rapidly changing conditions, we describe how the study of forest hybrid zones, using quantitative and genomic approaches, can facilitate conservation of genetic diversity and long-term species management. Full article

Forest products are commodities and subject to cyclical trends; yet resource-hungry countries offer exporters a period of sustained growth for those with the right products. Products have their distinctive requirements, e.g., finishing timber (colour, stability), structural (strength stiffness, stability), paper (fibre length and tear strength). The failure to incorporate such key properties in radiata pine (Pinus radiata) breeding programmes has been a lost opportunity for New Zealand forestry that constrains exports. Radiata pine remains a utilitarian, undifferentiated commodity. A complementary opportunity in international markets lies in naturally-durable eucalypts grown on New Zealand’s east coast drylands. These are species whose properties mimic those of the finest tropical hardwoods that are in most demand in Asian markets. Full article