Genetics and tree improvement

Forest genetics research helps improve the quality of second-growth forests and minimize losses due to pests and disease, and it informs how we can adapt our forest management activities in response to climate change.

Proceedings of the IUFRO 2019 Joint Conference: Genetics of Five-Needle Pines and Rusts of Forest Trees  - TR144

This guide provides detailed, step-by-step instructions on how to carry out the controlled mating of western redcedar (Thuja plicata Donn ex D. Don). The traditional tree breeding techniques presented are those used at the Cowichan Lake Research Station on south-central Vancouver Island, British Columbia, where western redcedar has been actively bred for more than three decades. This unique, tool-rich guide was created to help with training and information retention and transfer. It begins with a brief description of tree breeding objectives, a comparison of greenhouse versus outdoor breeding, and timelines for breeding activities, which serve to help frame and plan the many tasks. Nine breeding activities are introduced in chronological order: strobili induction, strobili production survey, phenology survey, female isolation, pollen management, pollination, cone protection, cone collection, and seed processing and storage. Important aspects of timing, as well as tools, techniques, methods or decision keys, relevant background or biological information, and supply lists are presented for each activity. The need for careful observation and precise timing as they relate to phenology is emphasized. The last chapters provide information on breeding crop production and maintenance, such as growing media formulations, container sizes, pruning and topping, and temperature requirements for indoor-grown stock.

Proceedings of the IUFRO 2019 Joint Conference: Genetics of Five-Needle Pines and Rusts of Forest Trees  - TR142

The nine species of white pines that are native to the United States or Canada are highly susceptible to white pine blister rust caused by the fungal pathogen Cronartium ribicola. Resistance breeding is considered to be the best tool to help ensure that our future forests will continue to have white pine species present. The U.S. Department of Agriculture Forest Service’s Dorena Genetic Resource Center has been involved in resistance evaluation and breeding for more than 50 years and has evaluated all nine species, to varying extents, with an emphasis on species occurring in the west. Seed orchards have been established for several species, while collections from genetically resistant parent trees in the forests are being used for some species for restoration and reforestation. Genetic resistance exists in the white pines, but the type of genetic resistance and its level varies by species. Major gene resistance has been characterized in four species (sugar pine [Pinus lambertiana], western white pine [P. monticola], southwestern white pine [P. strobiformis], and limber pine [P. flexilis]), while all nine species appear to have some degree of quantitative disease resistance. The lessons learned through the resistance breeding program, including from the assessment of longterm field trials, provide guidance on rust hazard and the durability, stability, and usability of resistance; potential opportunities for the future; and guidance to land managers about using resistance. Some misconceptions from the past about major gene resistance, virulence, and level of resistance are also discussed. Lessons learned over this period can also provide valuable inputs to applied resistance programs for other pathogens or pests.

Verifying Genetic Gain Estimates in Coastal Douglas-fir in British Columbia  - EN104

Before parent trees are included in seed orchards, their offspring are tested in progeny tests over several sites in the zones where the seed orchard seed is to be deployed. Parent trees are selected based on the performance (height growth, survival, stem and/or tree form, and other factors such as pest or disease resistance) of their offspring across all test sites. Within these progeny tests, many parent trees with very different growth potentials are grown together; however, only the best few will be selected at a test age of 10-15 years. Due to this type of test design, it is possible that fast-growing seedlings are surrounded by slowergrowing seedlings, potentially leading to height differences that are exaggerated due to competitive effects. The seedlings that will grow fastest will do so partially at the cost of their neighbours. As a result, the genetic superiority of the test seedlings, and consequently their parents, may be overestimated and may not be realized when seedlings from orchard parents are grown together in an operational plantation.

At the time of selection, a measure of each parent’s genetic quality is estimated based on the differences in overall performance of their offspring (progeny) across all test sites relative to the performance of a test control seedlot obtained from wild stands. This estimate of a parent tree’s genetic quality is termed its breeding value and reflects the expected growth increment in volume at rotation age 60.

Realized genetic gain tests are established to verify the estimated genetic quality of parent trees (parental breeding values) based on progeny tests by growing seedlings from parent trees of similar genetic quality together in large blocks (as in an operational plantation planted with orchard seed). The select seedlots are then compared to the growth of blocks established with seedlings grown from seed collected in naturally regenerated stands (Woods et al. 1995; Dhakal et al. 1996; St. Clair et al. 2004; Ye et al. 2010).

In this extension note, we describe the results of a realized genetic gain test planted on six low-elevation sites in British Columbia using coastal Douglas-fir of three distinct genetic classes. To evaluate possible effects of spacing and early onset of competition, the tests were established at four spacings, two of which are generally not used in operational forestry.

Forest Tree Genetic Conservation Status Report 2: Genetic Conservation Status of Operational Tree Species  - TR54

The native tree species of British Columbia provide a vast range of economic benefits and ecological services. Conserving genetic diversity in these species is critical for maintaining the ability of populations to adapt to new conditions, and for safeguarding genetic resources from which tree breeders can select to meet new challenges or objectives. Genetic conservation of forest trees is achieved in British Columbia for all indigenous species through the protection of populations in situ in parks and protected areas. The status of tree species in situ is documented in a companion report, Forest tree genetic conservation status report 1: In situ conservation status of all indigenous British Columbia species (Chourmouzis et al. 2009).

For species of economic importance that have genetic management and tree improvement programs, there are also extensive genetic resources archived ex situ, primarily in seed collections in long-term storage, and inter situ, in provenance and progeny trials. Historically, seed bank conservation samples have been obtained from the surplus remaining for each operational seedlot, after testing. Prior to December 2003, operational seedlots represented collections from over 50 individuals in an area. To support a more strategic acquisition approach subsequent collections focussed on obtaining at least three samples per target species within identified biogeoclimatic (BGC) zones. The strategy is to populate the full matrix of species-zone occurrences with at least three samples per cell for conservation collections. This represents a highly efficient, robust conservation approach: 100 grams of hybrid white spruce seed could contain up to 50,000 unique genotypes, and ex situ collections are not susceptible to climate change impacts, as genetic resources in situ and inter situ sites are; however, stocks must be periodically replenished because long-term storage may reduce seed viability.

This report summarizes the in situ, ex situ, and inter situ genetic conservation status of commercial forest tree species in British Columbia that have genetic management and tree improvement programs. These eight conifers have breeding programs supported by inter situ trials established for their respective seed planning zones (SPZs) and/or seed planning units (SPUs) (Snetsinger 2004).

Forest Tree Genetic Conservation Status Report 1: In Situ Conservation Status of All Indigenous British Columbia Species - TR53

The primary strategy for long-term conservation of British Columbia's biodiversity is through an extensive network of protected areas (pas). These parks and ecological reserves have been established in all of the major ecological units within the province. The driver behind such a "coarse filter" conservation approach is usually the conservation of species. Conservation of genetic diversity within species often receives relatively little attention, yet it is genetic diversity within populations that provides the capacity for native species to adapt to new environmental conditions. This is particularly important given the predicted rates of climate change for British Columbia in the next century.

In this document we evaluate how well British Columbia's protected areas meet the goal of conserving genetic diversity of all indigenous tree species in all major biogeoclimatic units (zones) in which they occur. Most tree species have high levels of genetic diversity but also show clinal variation with latitude, elevation, or distance to the ocean, which allows for adaptation to temperature and moisture conditions. Ensuring that several large populations are conserved within each major ecological unit should conserve high levels of genetic diversity and enable adaptation to rapidly changing conditions.

Thresholds for adequate conservation have been developed based on population genetic theory. This approach evaluates minimum effective population sizes needed to maintain current levels of genetic diversity indefinitely under an equilibrium between losing genetic variation due to genetic drift and gaining genetic variation via mutation. Population sizes presented in this document are estimates based on provincial botanical plot data extrapolated across ecological units, derived from species cumulative cover rather than population size (which is not directly measured during ecological data collection). We used the cumulative cover of species to estimate numbers of mature individuals; therefore, these estimates include unquantified errors and
do not fully reflect differences in tree stature and spatial distribution among species, ecosystems, and ages.

Developing Sitka spruce populations for resistance to the white pine weevil: summary of research and breeding program - TR50

This publication reports on the results of over two decades of research in the Sitka Spruce Breeding Program. The objective of the Sitka spruce (Picea sitchensis [Bong.] Carr.) breeding program is to develop, propagate, and deploy genotypes with robust resistance to the white pine weevil (Pissodes strobe Peck). The program is based on research that has been conducted on the extent and nature of genetic resistance in Sitka spruce populations in British Columbia. This research has international stature and provides a successful model for incorporating the results of research on natural genetic resistance to insect pests into applied breeding programs and proactive forest management.

Early Genetic Gains Verified in Realized-gain Trials of Coastal Douglas-fir and Western Hemlock - EN01

Coastal Douglas-fir and western hemlock breeding programs began in the late 1960s with the selection of better trees from natural stands throughout the coastal area. Extensive breeding and testing of these selected parents was carried out to learn more about genetic diversity patterns and performance stability, and to identify which parent trees produced offspring with superior performance potential.

The testing programs allowed identification of superior parents from the original selections made in natural stands (Table 1). Information on the long-term growth and yield of offspring from these parents is needed to better predict volume and value gains relative to natural-stand seed. Data are also needed to assist with the adjustment of growth models to account for genetic gains. The first series of trials to provide this information for Douglas-fir and western hemlock was planted in 1992.