Academic literature on the topic 'Tree improvement (incl. selection and breeding)'

The breeding of forest trees is only a few decades old, and is a much more complicated, longer, and expensive endeavor than the breeding of agricultural crops. One breeding cycle for forest trees can take 20–30 years. Recent advances in genomics and molecular biology have revolutionized traditional plant breeding based on visual phenotype assessment: the development of different types of molecular markers has made genotype selection possible. Marker-assisted breeding can significantly accelerate the breeding process, but this method has not been shown to be effective for selection of complex traits on forest trees. This new method of genomic selection is based on the analysis of all effects of quantitative trait loci (QTLs) using a large number of molecular markers distributed throughout the genome, which makes it possible to assess the genomic estimated breeding value (GEBV) of an individual. This approach is expected to be much more efficient for forest tree improvement than traditional breeding. Here, we review the current state of the art in the application of genomic selection in forest tree breeding and discuss different methods of genotyping and phenotyping. We also compare the accuracies of genomic prediction models and highlight the importance of a prior cost-benefit analysis before implementing genomic selection. Perspectives for the further development of this approach in forest breeding are also discussed: expanding the range of species and the list of valuable traits, the application of high-throughput phenotyping methods, and the possibility of using epigenetic variance to improve of forest trees.

The Chinese chestnut (Castanea mollissima Blume) is a valuable germplasm resource for horticultural traits such as resistance to chestnut blight (Cryphonectria parasitica), excellent quality, wide adaptation, and consistent high yield. The Chinese chestnut breeding program was established at Auburn Univ. in 1933 from nuts directly introduced from China by the USDA. A recurrent selection breeding program with progeny from the 1933, 1953, and 1991 plantings with selection for blight resistance, precocity, nut size, and storage quality, yield, and pest resistance. Cultivars released from the 1933 planting were `Alaling,' `Alamore', and `Black Beauty'. `AU-Cropper', `AU-Leader', and `AU-Homestead' were named from the 1953 planting. Two blight-resistant, precocious seedlings, AU-91-P1-26 and AU-P4-26, appear to be very promising selections for improvement of all Chinese chestnut cultivars for nut size and other selection traits. Since there is little information available regarding heritability of certain traits in perennial tree species, results of 65 years of breeding at Auburn Univ. should provide us with guidance for further improvement of selection traits in chestnut breeding.

Time is a major constraint in the progress of tree improvement programs. Four ways in which time influences the tree improvement process are (i) evolutionary time, (ii) time to harvest, (iii) time to achieve phenotypic stability, and (iv) time to reach reproductive maturity. The ways in which each of these affects the three phases of a tree improvement program (conservation, selection and breeding, and propagation) are identified and discussed. How biotechnological techniques, as well as other enabling technologies, address the time constraint problem is also discussed. The biotechnological approaches include tissue culture, molecular genetics, and genetic engineering; the enabling technologies include early testing and flower induction. Through tissue culture it is possible to increase genetic gain per unit time and increase total genetic gain by using more of the total genetic variation. Development of high-resolution linkage maps, through application of molecular genetics technology, will provide new approaches to early screening, testing, and selection. Additionally, molecular probes will be useful in improving methods that genetically fingerprint germ plasm. Genetic engineering has considerable potential to reduce time constraints. However, because of the diverse breeding and production populations typically employed, much basic work needs to be done to integrate genetically engineered materials into tree improvement programs. Early selection and flower induction address the time constraints imposed by age-stable performance and reproductive maturity. When used in combination with the previously described biotechnologies, a powerful system is created that can dramatically reduce the time required to integrate genetically improved material into forest regeneration programs. An example of integrating tree improvement, clonal forestry, and biotechnology is described for an existing black spruce regeneration program.

Earlier breeders used phenotypic selection based on morphological characteristics to improve tree varieties. These selections often take many cycles of breeding and backcrossing in order to place desired characteristics. But today the knowledge has paved the way for a much deeper understanding of the mechanics of cell biology and the hereditary process itself. Breeders are presented with numerous possibilities of altering the behaviour of existing varieties. Linkage between molecular markers can be translated to genetic linkage maps, which have become an important tool in plant genetics. They may choose to use marker-assisted approaches in order to facilitate the selection of favourable combinations of genes that occur naturally within a tree species.  

Biotechnology, which has made significant contributions to the improvement programs of agronomic crops, offers the opportunities to enhance forestry research and accelerate tree improvement. Forest biologists and tree breeders are turning their attentions to these biotechnologies, which enable them to overcome barriers and can be integrated into conventional breeding methods leading to more rapid progress in tree breeding. Plant biotechnology currently comprises a range of activities, such as vegetative propagation and tissue culture, genome analysis and gene cloning, DNA recombination and gene transfer, and DNA-based selection. Although application of biotechnology in forest trees and ornamental woody plants is just in its infancy, micropropagation is rapidly becoming a standard tool for tree improvement. In addition, emerging success and practical application have become visible in genetic transformation. These initial achievements have already proven that biotechnology will make inestimable impact on tree improvement.

With the birth of classical genetics, forest genetic breeding has laid a foundation in the formation of the basic theories of population genetics, quantitative genetics, cytogenetics, and molecular genetics. Driven by the rapid growth of social demand for wood and other forest products, modern genetics, biotechnology, biostatistics, crop and animal husbandry breeding theories, and technical achievements have been continuously introduced for innovation, thus forming a close combination of genetic basic research and breeding practice. Forest tree breeding research in the world has a history of more than 200 years. By the middle of the 20th century, the forest tree genetic breeding system was gradually formed. After entering the 21st century, the in-depth development stage of molecular design breeding was opened. With the continuous improvement of traditional genetic breeding methods, emerging modern bioengineering technology has also continuously promoted the development of forest genetic breeding. This study mainly summarizes the research history of forest tree genetics and breeding, as well as discusses the application of modern bioengineering technology represented by genome selection and gene editing in forest tree breeding, so as to provide better reference for forest tree breeding research.

SummaryAn innovative approach to tree breeding called ‘breeding without breeding’ (BWB) is presented. The method, as applied on the material in hand, allows the capture of 75–85% of the genetic response to selection attained through conventional programmes without the need to do any controlled pollination and simplified or possibly no experimental field testing: both considered to be the most resource-demanding activities in breeding programmes. BWB combines the use of genotypic or phenotypic pre-selection of superior individuals, informative DNA markers for fingerprinting and pedigree reconstruction of offspring to assemble naturally created full- and half-sib families resulting from mating among selected parents, and quantitative genetics analyses to identify elite genotypes for further genetic improvement or the establishment of production populations. BWB utility is demonstrated using a retrospective study of Douglas-fir (Pseudotsuga menziesii) progeny tests consisting of offspring produced from 150 controlled crosses among 60 parents and established over three sites. The empirical results are supported by theoretical expectations demonstrating anticipated minimum genetic response compared with conventional approaches. The method's simplicity offers an exceptional opportunity for the development of comparable breeding efforts in developing countries, advanced and new breeding programmes, and economically important and ‘minor’ species.

SynopsisSitka spruce is a monoecious, wind-pollinated, cross-fertilising species showing wide genetic variation which suggests heterozygosity for many alleles and natural selection against self-fertilisation. Phenotypic selection for the important trait of vigour is ineffective, so testing progenies of selected individuals and clonal testing is an essential and time-consuming part of any improvement programme. Old trees can be vegetatively propagated by grafting and very young trees by rooted cuttings.The British tree improvement programme is based, in the short term, on the use of seed collected from superior plantation trees of desirable origins; in the mid term on seed derived from clonal orchards based on mixtures of clones previously tested for superiority in family tests; and in the longer term on highly superior seed or clones derived from a system of recurrent mating with family selection. Three populations are being developed. There is a small interspecific hybridisation programme.

Tree breeding is an important component of tree improvement which involves the application of genetic principles for the mass production of seedlings with desired traits in order to achieve higher productivity, better adaptability of the environment and vigorous growth rate. It helps in increasing yields and shortened rotations so it has a large potentiality to supply timber and wood demand of the world. Species choice, provenance selection and propagation method are the major aspects of tree breeding. Plus tree selection, progeny testing, provenance test and vegetative propagation have been used since early of civilization and often regarded as conventional tree breeding techniques while seed orchards, clonal propagation, somatic embryogenesis, micro-propagation or in-Vitro propagation, and biotechnology are modern tree breeding techniques. Different countries have been developing tree breeding techniques and achieving maximum benefits from it. Southeast Asia is using Acacia mangium, A. crassicarpa, Gmelina arborea, and Eucalyptus spp.; Populus deltoids, Casuarina equisetifolia, Eucalyptus spp. have been using by India; Teak has been vegetative propagated in Thailand; Salix babylonica has been growing in Greece for biomass production. Increasing yield and shortened rotation are the major prospects while loss of genetic diversity, higher production costs and requirement of constant upgrading are the major hindrances of tree breeding. DOI: http://dx.doi.org/10.3126/init.v5i0.10266 The Initiation 2013 Vol.5; 153-163

Abstract For the past 10 years, new attention has been given in Romania to the development of improved fruit tree rootstocks by hybridization and mutation breeding. Prior to 1976, rootstock improvement was focused primarily on selection in seedling populations derived from both wild and cultivated forms, with emphasis on adaptation to local soil and climatic conditions. The rootstocks now in commercial use in Romania come from these sources.

The heritability of microfibril angle (MFA) in loblolly pine, Pinus taeda L., and its genetic relationships with height, diameter, volume and specific gravity were examined in two progeny tests with known pedigrees. Significant general combining ability (GCA), specific combining ability (SCA), and SCA x block effects indicated that there are both additive and non-additive genetic influences on MFA. Individual-tree narrow-sense heritability estimates were variable, ranging from 0.17 for earlywood (ring) 4 MFA to 0.51 for earlywood (ring) 20 MFA. Genetic correlations between MFA, specific gravity and the growth traits were non-significant due to large estimated standard errors. Multiple-trait selection and breeding in a mainline and elite population tree improvement program were simulated using Excel and Simetar (Richardson 2001). The effects of four selection indices were examined in the mainline population and the effects of seven selection indices and four breeding strategies were examined in the elite population. In the mainline population, selection for increased growth caused decreased wood quality over time. However, it was possible to maintain the overall population mean MFA and mean specific gravity at levels present in the base population by implementing restricted selection indices. Likewise, selection for improved wood quality in the elite population resulted in decreased growth unless restricted selection indices or pulp indices derived from those of Lowe et al. (1999) were used. Correlated phenotypic responses to selection on indices using economic weights and heritabilities were dependent on breeding strategy. When a circular mating system (with parents randomly assigned to controlled-crosses) was used, the index trait with a higher economic weight was more influential in determining correlated responses in non-index traits than the index trait with a lower economic weight. However, when positive assortative mating was used, the index trait with a greater variance was more influential in determining correlated responses in non-index traits than the index trait with a lower variance regardless of economic weight.

Wheat is a major source of calories and protein for humans worldwide. Wheat is the most widely grown crop, with cultivation areas and production systems on every continent. The cultivated land area is vast because of its importance and adaptability to various environmental conditions. Global wheat production has not kept up with the growing population, provoking the need to develop new methods and techniques to increase genetic gains. The first research chapter of this Ph.D. dissertation involves performing genome-wide association studies (GWAS) to identify and examine transferability of marker-trait associations (MTAs) across environments. I evaluated yield and yield components traits among 270 soft red winter (SRW) wheat varieties. The population consists of experimental breeding lines adapted to the Midwestern and eastern United States and developed by public university breeding programs. Phenotypic data from a two-year field study and a 45K-SNP marker dataset were analyzed by FarmCPU model to identify MTAs for yield related traits. Grain yield was positively correlated with thousand kernel weight, biomass, and grain weight per spike while negatively correlated with days to heading and maturity. Sixty-one independent loci were identified for agronomic traits, including a region that with –logP of 16.35, which explained 18% of the variation in grain yield. Using 12 existing datasets from other states and seasons, in addition to my own data, I examined the transferability of significant MTAs for grain yield and days to heading across homogenous environments. For grain yield and days to heading, I only observed 6 out of 28 MTAs to hold up across homogenous environments. I concluded that not all marker-trait associations can be detected in other environments.

In the second research chapter of this Ph.D. dissertation, I dissected yield component traits under contrasting nitrogen environments by using field-based low-throughput phenotyping. I characterized grain yield formation and quality attributes in soft red winter wheat. Using a split-block design, I studied responses of 30 experimental lines, as sub-plot, to high nitrogen and low nitrogen environment, as main-plot, for two years. Differential N environments were imposed by the application, or lack thereof, of spring nitrogen application in a field, following a previous corn harvest. In this study, I measured agronomic traits, in-tissue nitrogen concentrations, nitrogen use efficiency, nitrogen harvest index and end-use quality traits on either all or subset of the germplasm. My data showed that biomass, number of spikes and total grain numbers per unit area were most sensitive to low nitrogen while kernel weight remained stable across environments. Significant genotype x N-environment interaction allowed me to select N-efficient germplasm, that can be used as founding parents for a potential breeding population specifically for low-N environments. I did this selection on the basis of superior agronomic traits and the presence of the desirable gluten quality alleles such as Glu-A1b (2*) and Glu-D1d (5+10).

Due to overpopulation and resource-poor habitat structure, deer threaten the future of oak and other browse-sensitive species in hardwood forests. Appropriate tools must be used to ensure desirable, diverse, and ecologically stable regeneration of future forests and the sustainability of native plant communities. We performed two experiments and a review to examine the effectiveness of available methods for managing browse of hardwood seedlings and to discover how these interact with each other and other silvicultural methods. First, we examined how fencing interacts with controlled-release fertilization, seed source (genetically select and non-select), and site type (afforested and reforested sites) to enhance the regeneration of planted northern red oak (Quercus rubra L.), white oak (Quercus alba), black cherry (Prunus serotina), and black walnut (Juglans nigra) at five sites in Indiana. Fencing proved to be the greatest determinant of seedling growth, survival, and quality. Fertilizer enhanced the early growth of white oak and black cherry, though for black cherry this occurred only inside fences. Select seed sources grew better and showed greater quality; however, the survival of select seedlings was limited by deer browse in absence of fences. Trees at afforested sites had lower survival if left non-fenced. Secondly, we also investigated how fencing and invasive shrub removal affected natural regeneration, species richness, and ground-layer plant cover under closed-canopy forests. Honeysuckle (Lonicera maackii) removal had a variable effect depending on species and site. Positive effects were most common for shade-intolerant species, while negative effects occurred for a few shade-tolerant species at some sites. Deer fencing had a positive effect on cherry and hackberry seedling density, and a negative effect on elm seedling density. Honeysuckle and deer fencing interacted antagonistically in some instances. Fencing without honeysuckle removal resulted in lower elm abundance and herbaceous-layer cover. In the densest invasions, leaving honeysuckle intact resulted in a complete lack of recruitment into the sapling layer. Our experiment suggests that invasive shrub removal and fencing be done together. Finally, we synthesized the existing literature on browse management options for hardwood regeneration to evaluate their relative effectiveness. Fences, tree shelters, repellents, facilitation by neighboring plants, deer population control, timber harvest, and slash all had positive effects on height growth of regenerating seedlings under deer browse pressure. Fences were more effective at reducing browse than repellents, while fertilizers increased browse and had no effects on growth.

Australia's unique and diverse woody flora has become socially, economically and environmentally important in many other countries. The seed of some Acacia species showing promise in planting programs in semi-arid areas has been a part of the traditional diet of Australia's Aboriginal people. The dry seed may be ground to flour, mixed with water and eaten as a paste or baked to form a cake. Forest tree breeding has focussed on wood production, selecting taller, faster-growing varieties. The same principles of selection and improvement can be applied to improve seed yields and nutritional properties of shrubs. The selection criteria would include seed characters such as taste, seed coat thickness and nutritive value to maximize their food value. The book looks at the possibility of building upon the traditional knowledge of Aboriginal Australians, using modern scientific methods, for the benefit of people in the world's dry areas. Australian Dry-zone Acacias for Human Food documents the proceedings of a workshop held at Glen Helen, Northern Territory, Australia. The purpose of the meeting was to examine the idea of developing the food value of the seed of Australia's dry-zone acacias. This book covers a summary of the workshop conlcusions, the invited papers, and recommendations of the working groups.

A wide range of exotic conifer species have been successfully introduced in Kenya since 1910 for the purpose of supplying wood, mainly for timber, pulp, and plywood industries. Among the conifers introduced, Cupressus lusitanica and Pinus patula have adapted well to local growing conditions and are now the key species widely planted in commercial plantations. The other conifer species are planted at secondary level or as ornamentals. In order to increase productivity, the key conifer species have been subjected to genetic improvement through selection, breeding, and hybridization. Results of tree improvement work on C. lusitanica and P. patula showed growth and productivity increase from 20 to 25 m3/ha/yr. for C. lusitanica and from 25 to 30 m3/ha/yr. for P. patula. Scaling up conifer plantations using the tree improvement technologies drawn for the two species is one of the strategies for closing the annual wood supply–demand deficit which is currently estimated at 10.3 million m3. It is also one of the strategies for achieving 10% tree cover which is currently at 7.2%. The strategy encompasses the application of principles of tree breeding, improved germplasm, silviculture, pests and disease control. This presentation is a review of the status of conifer species since their introduction in Kenya.