R. D. Burdon

Achievements in forest tree genetic improvement in Australia and New Zealand 10: Pinus radiata in New Zealand

Summary Pinus radiata is the subject of much the largest and longest-running tree breeding program in New Zealand. Very intensive plus-tree selection began in the early 1950s, the first seed orchard planting was in 1958, and the first orchard seed was collected in 1968. By 1985 seed orchards could meet the national planting needs, which helped prompt an innovative seed certification scheme. Selection began in local, ‘land-race’ stands. That proved appropriate, but better knowledge led to research on material from the species’ entire natural range and then to further seed importations from natural stands, mainly for future genetic resources. Initial plus-tree selection largely addressed poor tree form in the central North Island. This led to selecting a ‘short-internode’ (‘multinodal’) branching ideotype, with great improvements in general tree form and substantial gains in growth rate. A distinctive portfolio of several breeds, representing different breeding goals, has since been developed for the diverse planting sites and the various end products. By contrast, the original regionalisation of seed orchards proved largely unjustified. Despite early research indicating good heritabilities, wood properties have figured significantly in breeding goals only since growers substantially reduced harvest ages, but they are now intensively researched. The breeding program was greatly expanded from 1968 to meet the needs of multi-generation breeding. This was one of the programs contributions to developing breeding strategy as a discipline, various of which were reflected in the 1986 Development Plan. Industry uptake of tree breeding has since posed challenges in maintaining genetic variability for a secure, long-term underpinning of the program. Special genetic-gain trials were first planted in 1978, to demonstrate and quantify genetic improvement, and to help update forest out-turn predictions. The gains achieved in tree form helped induce New South Wales State to affiliate with the New Zealand program, following significant earlier contributions of breeding material to Australian breeding programs. Improved technologies for seed orchards and vegetative propagation have facilitated development of the breed portfolio and more specific customisation of seedlots. Becoming able to deliver genetic gain through controlled pollination has allowed changes in the structure of the breeding population. Further changes are resulting from an increasing capability to reconstruct pedigrees after open pollination. Developments towards full clonal forestry have faced obstacles, but offer greater genetic gains and a more precise customisation, and clonal forestry is now being vigorously commercialised. Having a single, large Forest Service until 1987 undoubtedly favoured the development of a very strong tree improvement program. Since then, continuing institutional changes, which are reviewed, have posed numerous challenges.

Implications of selection history on genetic architecture of growth, form, and wood-quality traits in Pinus radiata

Clonal trials of Pinus radiata D. Don (radiata pine), representing two populations (or breeds), one selected for growth and form (GF) and the other selected for high wood density as well as growth ...

Population management: potential impacts of advances in genomics

Even with advanced gene technologies continued population improvement remains a key foundation for future genetic gain in forest trees. Currently, this is served by maintaining genetic diversity while capturing genetic improvement, often through structuring populations into a genetic hierarchy, setting population sizes, and managing pedigrees and inbreeding. In the future, information from genomic technologies will complement classical approaches, such as common-garden field experiments, for characterizing the genetic base and measuring and monitoring genetic diversity. This will entail directly measuring DNA sequence diversity of both selectively neutral markers and functional genes. Calibrating neutral marker diversity against functional diversity will become easier with functional genomics. For maintaining pedigree and managing inbreeding, genomic information can be used to relax some traditional tenets of population management. With future knowledge of functional polymorphisms, the better understanding of the nature and origins of genetic variation should enhance management of populations to both conserve genetic diversity and exploit it by more efficient selection. Where fungal diseases threaten biotic crises, very large populations may be needed, the requisite sizes often being very uncertain. Gene discovery holds enormous promise, but depends heavily on comparative genomics, capitalizing on genomic information from Arabidopsis, Populus and Eucalyptus, and the increasing numbers of accessible ESTs. Much greater insights into non-codon mutational processes and rates should also guide population management. A key challenge, however, will be to utilize information and apply tools cost-effectively. Also, very detailed genomic information, exemplified by the poplar-genome sequencing, may allow earlier adaptation of technology and development of new information in angiosperms than in gymnosperms.

Gene-assisted selection: applications of association genetics for forest tree breeding

This chapter describes application of association genetics in forest tree species for the purposes of selection. We use the term gene-assisted selection (GAS) to denote application of marker–trait associations determined via association genetics, which we anticipate will be based on polymorphisms associated with expressed genes. The salient features of forest trees are reviewed, including existing and somewhat limited knowledge of linkage disequilibrium (LD), as well as genomic information for both conifers and hardwoods. The relatively short span of LD in largely undomesticated and outbred forest tree species offer good prospects for precisely locating quantitative trait nucleotide (QTN), but necessitates wise candidate gene selection and generation of nongenic

Deterministic Simulation of Gains for Seedling and Cloned Main and Elite Breeding Populations of Pinus radiata and Implications for Strategy

Abstract Genetic gains in breast-height diameter were estimated using deterministic simulation. Simulations of gain from one generation of selection were undertaken in large Main and small Elite breeding populations for a range of heritabilities, with varying numbers of parents, families, seedlings/family, clones/family and ramets/ clone to aid revision of the New Zealand Pinus radiata breeding strategy. Cloned versus seedling populations of equal numbers of plants were simulated, derived from open pollination, polycrossing, and pair crossing. Balanced within-family selection was used for 200, 400 and 800-parent Main breeding populations and among- and within-family selection for 25-parent Elite populations of 25 up to 100 full-sib families. Predicted gains from within-family selection in the Main population were highest from cloned polycross families at all heritabilities and lowest for seedling fullsib families. Gains from cloned populations were higher than seedling equivalents at heritabilities ≤0.5, and their advantage in gain was greatest at lower heritabilities. Elite populations of 25 parents showed similar trends but intensive among- and within-family selection resulted in much higher gains than from the Main, highest from the cloned options. The increase in gain with increased number of families diminished with more than 2-3 times as many families as parents. A new strategy was proposed for P. radiata, based on the simulation results, involving an expanded Main breeding population of open-pollinated (OP) seedling families, together with pair-cross family seedlots already available, supported by parentage reconstruction using DNA markers. Forwards selection in small cloned Elite populations was proposed as the main source of seed orchard clones.

Implications of non-linear economic weights for breeding

SummaryRelationships were studied theoretically between phenotypic values of selection candidates (‘parents’) and economic worth of the ‘offspring’ that would belong to production populations. The candidates could include individuals, crosses or clones, and the offspring could be produced either sexually or vegetatively. Cases considered included: three systems for generating production populations [clonal propagation, pair(full-sib)crosses and half-sib crosses]; three economic-worth (profit) functions for individual offspring (linear, intermediate optimum, acceptable versus cull); and independently varying heritabilities for both parents and offspring. The heritabilities were varied in the model against a background of fixed genetic variance. Parental values were considered in terms of phenotypic standard deviations from the population mean, assuming normality. Lower heritabilities and, to a lesser extent, genetic segregation severely damped down the non-linearities of economic worth in relation to measured parental values, such that the linear weightings for traits in a selection index should usually be a good approximation, provided the profit function for individual offspring is monotonic. The economic advantages of corrective mating within a select population may be minimal if both heritabilities are low and the profit functions apply to individual offspring. The economic advantages accruing from genetic uniformity of clones (or crosses between inbreds) in conjunction with non-linear profit functions are strongly dependent on achieving high broad-sense heritabilites, particularly in the offspring (production population).

Responses to Inoculation With Diplodia Pinea in Progenies of Apparently Resistant Trees of Pinus Radiata

A glasshouse inoculation trial with Diplodia pinea (Desm.) Kickx was carried out on 20 wind-pollinated progenies of Pinus radiata D. Don. The parents had been selected on a site of very high disease incidence for freedom from Diplodia-associated shoot dieback. Compared with two control seed lots the progenies as a whole showed less infection after an inoculation than the controls (69.7% v. 79.6%), this difference being statistically significant (P <0.05) in even the most stringent tests. The contrast was somewhat less marked in respect of shoot dieback (36.8% v. 44.4%). The progenies, however, were strongly variable among themselves, ranging from substantially less affected than the controls to marginally more affected. This suggests that there were some cases of real resistance with an additive genetic basis, although infection response seems to be only weakly heritable at the level of the individual.

Short Note: Coefficients of Variation in Variables with Bounded Scales

Abstract With a variable that is recorded on a scale with fixed bounds, it can be appropriate to use for the denominator of the coefficient of variation the square root of the (sign-independent) product of the differences between the mean and the two bounds of the scale. A simple illustrative example is given.

Family variation and potential for genetic gain in frost resistance of Pinus radiata

Twenty-three Pinus radiata seed orchard clones of the New Zealand “850” series were each control-pollinated with a mix of 10 pollens to produce polycross families. The seed was sown in open nursery beds. Seedlings were potted up at six times of the year and subjected to white advective frosts in controlled-environment rooms, with up to seven frosting runs of variable severities at each time. There were significant differences (p< <0.001) between families in frost injury, such that, although there was statistically significant family × time interaction, some families were consistently more frost resistant (tolerant) than others. No association between frost resistance and growth rate was evident.Individual-tree heritability estimates for frost damage scores were around 0.3 at given times, and 0.20 over all times. Prospective gain in resistance from progeny testing over several seasons of the year, with 2:23 selection, is about 1°C. An additional gain of 0.4°C resistance appears obtainable from 1:90 selection of individuals within pair-crosses in a single frosting run. This additional (within-cross) gain might be increased to around 0.75°C, with the same culling rate but testing one ramet per seedling at each of four times of the year.

Genotype by environment interactions in forest tree breeding: review of methodology and perspectives on research and application

Genotype by environment interaction (G×E) refers to the comparative performances of genotypes differing among environments, representing differences in genotype rankings or differences in the level of expression of genetic differences among environments. G×E can reduce heritability and overall genetic gain, unless breeding programmes are structured to address different categories of environments. Understanding the impact of G×E, the role of environments in generating G×E and the problems and opportunities is vital to efficient breeding programme design and deployment of genetic material. We review the current main analytical methods for identifying G×E: factor analytic models, biplot analysis and reaction norm. We also review biological and statistical evidence of G×E for growth, form and wood properties in forest species of global economic importance, including some pines, eucalypts, Douglas-fir, spruces and some poplars. Among these species, high levels of G×E tend to be reported for growth traits, with low levels of G×E for form traits and wood properties. Finally, we discuss possible ways of exploiting G×E to maximise genetic gain in forest tree breeding. Characterising the role of environments in generating interactions is seen as the basic platform, allowing efficient testing of candidate genotypes. We discuss the importance of level-of-expression interaction, relative to rank-change interaction, as being greater than in many past reports, especially for deployment decisions. We examine the impacts of G×E on tree breeding, some environmental factors that cause G×E and the strategies for dealing with G×E in tree breeding, and the future role of genomics.