D. Lindgren

Can viable pollen carry Scots pine genes over long distances

Abstract The hypothesis that gene flow northwards by long distance wind dispersal of pollen is a contributing factor in Scots pine (Pinus sylvestris L.) seed crops in northern Scandinavia (Umea) was examined. Pollen was observed in the air before local pollen shedding began. This pollen has been shown to germinate and is likely to be viable. This early pollen was probably not of local origin. Wind patterns and the geographic pattern of pollen shedding were such that it is likely that the origin of the early pollen was hundreds of km to the south. Since many of the female strobili are receptive to pollination before local pollen shedding occurred, early non-local pollen has an advantage over later local pollen. Thus, the gene flow caused by pollen migration is likely to be large enough to be of evolutionary significance.

Classifying seedlots of Picea sitchensis and P. glauca in zones of introgression using restriction analysis of chloroplast DNA

SummaryChloroplast DNA (cpDNA) restriction analysis was used to classify five reforestation seedlots as to species. The material included two Sitka spruce (Picea sitchensis (Bong.) Carr.), one white spruce (P. glauca (Moench) Voss) from interior British Columbia, and two putative hybrid seedlots from the coast-interior introgression zone in British Columbia. The cpDNA patterns generated by Bam-HI and Bc1-I from individual trees of Sitka spruce, white spruce, western white spruce (P. glauca var. albertiana (S. Brown)), and Engelmann spruce (P. engelmanni (Parry)) were species-specific. They were used as reference patterns for comparisons. In addition, two controlled crosses between white and Sitka spruce were analyzed to demonstrate the paternal inheritance of cpDNA in spruces. The cpDNA restriction patterns for the five seedlots were obtained from composite samples of seedlings from each lot and compared to the typical cpDNA patterns of each species. Restriction patterns for the two Sitka spruce seedlots agreed with those from the Sitka spruce tree, while patterns for the white spruce seedlots from British Columbia agreed with those from the white spruce tree, lacking evidence of any Engelmann spruce component in the sample. On the other hand, one putative hybrid seedlot showed cpDNA patterns similar to white spruce while the other showed fragments unique to both Sitka and white spruce, indicating that this was a hybrid seedlot. The analysis of cpDNA restriction polymorphism has proven to be an effective tool for classifying seedlots in regions of introgression. To our knowledge, these results provide the first demonstration of the use of cpDNA analysis for solving practical forestry problems.

Pollen migration into a seed orchard of Pinus sylvestris L. and the methods of its estimation using allozyme markers

Gene diversity and foreign pollen migration into a Scots pine seed orchard in northern Sweden were examined using allozyme markers. The gene diversity and fixation index varied among loci and the average values in embryos over 18 loci were 0.262 and 0.038 respectively. The observed pollen migration into the seed orchard was 30%. Two different methods were used to adjust the observed pollen migration for undetected foreign pollen. The pollen migration into the orchard after adjustment using these methods was 51% and 55% respectively. In addition, sampling procedure and other factors which can influence genetic parameters inferred from allozyme analysis are discussed.

Prediction of genetic gain and gene diversity in seed orchard crops under alternative management strategies

Abstract Genetic gain and the gene diversity of seed crops from clonal seed orchards were formulated considering genetic selection, fertility variation and pollen contamination, and compared for five different management strategies. Genetic response was studied as a function of orchard management tactics. Management variables included the proportion of clones left after genetic thinning and/or selective seed harvesting. Formulae were derived to calculate gene diversity (expressed as group coancestry or status number) based on the sex ratio in an orchard population. The influence of having different sets of clones serving as seed parents, or pollen parents, or as both, was analysed. In addition, the impact on genetic gain and the gene diversity of seed crops was studied quantitatively as a function of the quantity and quality of gene flow from outside the orchard. The negative impact of fertility variation among orchard genotypes on the gene diversity of the seed crop was quantified. Numerical examples were given to illustrate the impact of orchard management alternatives on genetic gain and gene diversity. The formulae and results of this study can be used for identifying favourable alternatives for the management of seed orchards.

Gene dispersion within a population of Pinus sylvestris

Gene dispersion within a population was studied in a 2‐hectare stand of 74 seed trees and 1100 seedlings. Isozyme markers were used to determine the genetic relationships among parental trees, embryos and seedling progenies. Paternity exclusion analyses were used to study multilocus progeny genotypes from certain parents. Results demonstrate large variation between trees in their capacity to contribute their genes through natural regeneration. The proportion of all genes dispersed into a specific distance interval from the source was estimated. The estimation procedure took into account the background of seedlings where parenthood was not excluded, but where the seedlings turned out to be unrelated. We found little evidence for clusters of progeny seedlings surrounding their parental tree. Within 15 m from a tree, approximately 5 % of the genes originated from that tree and 95 % originated from other trees. We found no evidence for an increase in levels of inbreeding, or genetic substructuring in the seed...

Variation in effective number of clones in seed orchards

The effective number of clones (Nc) wasestimated for 255 conifer clonal seed orchards in Finland, Korea, andSweden, based on the variation in the number of ramets among clones. Themean census number of clones (N) varied from 70, in 13 KoreanPinus koraiensis seed orchards, to 139 in 176 Finnish Pinussylvestris seed orchards. The mean effective number of clones(Nc) was 66, with a range from 10 to 421. One fifthof the orchards had Nc between 10 and 40, and twothirds between 41 and 160. On average, the relative effective number ofclones (Nr =Nc/N) was 0.74, with a range from 0.2to almost 1.0. Thus, the census number of clones in a seed orchard isgenerally rather informative, but the effective number of clones is moreinformative. Many of these first-generation seed orchards wereestablished with an intention to have near-equal numbers of ramets foreach clone. The use of effective number of clones may be more importantin future seed orchards and genetically thinned seed orchards.

Deployment to plantations of numbers and proportions of clones with special emphasis on maximizing gain at a constant diversity

SummaryThe value of a mixture of genetic entries present in different proportions is defined. A measure of the disadvantage of reduced diversity is defined as the sum of the squares of the proportions of the different entries. An algorithm for maximizing genetic gain of the mixture under the constraint of a constant disadvantage is developed. The optimal deployment strategy is one that lets the proportion of the genetic entries be linearly dependent on their genetic value. By use of rankits as entries for genetic values, optimal solutions for deployment were calculated for a range of values of available entries (from 10 to 5,000) and preset diversity-related disadvantage-factors (the preset values correspond to mixtures of between 2 and 100 entries in identical proportions). The values are tabulated so they can be used by breeders. The superiority of the proposed strategy increases with the proportion of the available entries which are selected. In the situation that around half would have been selected if truncation selection was applied, the improvement in genetic gain compared to classical truncation selection is up to 18%. Thus, considerable improvements in gain are possible without any sacrifice in diversity. Applications are discussed with particular reference to clonal forestry.

Optimal Clone Number for Seed Orchards with Tested Clones

Abstract The optimal number of clones in seed orchards is discussed. A model is constructed to maximize a goodness criterion (“benefit”) for seed orchards. This criterion is a function of: 1) the number of tested genotypes available for selection and planted in seed orchard; 2) the contribution to pollination from: a) the ramet itself; b) the closest neighbors; c) the rest of the orchard and sources outside the orchard (contamination); 3) variation among genotypes for fertility; 4) frequency of selfing; 5) production of selfed genotypes; 6) gene diversity (= status number); 7) influence of contamination; 8) genetic variation among candidates; 9) correlation between selection criterion (e.g. height in progeny test) and value for forestry (e.g. production in forests from the orchard); and 10) the number of clones harvested. Numeric values of the entries are discussed, and values were chosen to be relevant for scenarios with Swedish conifers (focusing on Scots pine) and for loblolly pine. Benefit was maximized considering the number of clones. The optimum was 16 clones for the Swedish scenario, while less for the loblolly pine scenario. The optimum was rather broad, thus it is not essential to deploy the exact optimum, and an approximate optimum will do. A sensitivity analyses was performed to evaluate the importance of the likely uncertainty and variation in different entries. Quantification of the benefit of gene diversity is important. Other significant considerations are the genetic variance in the goal character and the ability to predict it, as well as the impact of selfing and the variation in reproductive success between clones. Twenty clones is suggested as a thumb rule for Swedish conifers.

Marker-based parentage analysis facilitates low input ‘breeding without breeding’ strategies for forest trees

Controlled crosses and progeny testing are important components of tree breeding programs. Recently, a new approach, ‘breeding without breeding’ (BWB), has been proposed to obtain structured pedigrees for the breeding and testing from wind-pollinated progenies; the technique uses high-resolution markers instead of conventional approaches. The BWB approach is attractive for outcrossing conifers where the breeding cycle is long and reproductive maturity is often delayed. For the application of the BWB approach, the accurate assignment of parents is essential. The first step in the application of the BWB approach is to conduct tests into the reliability of paternity and parent-pair exclusion procedures in complex situations. In this study we conducted multi-locus-based empirical and simulation analyses for a Scots pine seed orchard crop, in order to develop the appropriate parentage assignment techniques for BWB and to investigate whether pedigrees from a seed orchard crop can be determined with sufficient accuracy. The results were promising, as 93–97% of the seeds generated by mating among the seed orchard clones were correctly assigned to a parent-pair. When mating occurred with foreign pollen, the success rate of identifying mother clones was 60–78%. Based on these results, we propose three novel low input breeding strategies for forest trees. The principles of the different options and their potential benefits and costs are described and discussed using Scots pine as a case study.

Evaluation of Pollen Contamination in an Advanced Scots Pine Seed Orchard

Abstract The pollination pattern in a Scots pine (Pinus sylvestris L.) seed orchard consisting of 28 clones was studied using nine microsatellite (SSR) loci. The nine SSR loci produced unique multilocus genotypes for each of the orchard’s 28 clones and allowed paternal assignment of the studied 305 seed using paternity exclusion probability of 99.9%. Fifty two percent of the studied seeds were sired by outside the orchard pollen sources (i.e., pollen contamination) and as expected, low selfing (2.3%) was detected. These results are valuable for the evaluation of the seed orchard function and the impact of contamination on the expected genetic gain.