Stability in and correlation between factors influencing genetic quality of seed lots in seed orchard of Pinus tabuliformis Carr. over a 12-year span

Coniferous seed orchards require a long period from initial seed harvest to stable seed production. Differential reproductive success and asynchrony are among the main factors for orchard crops year-to-year variation in terms of parental gametic contribution and ultimately the genetic gain. It is fundamental in both making predictions about the genetic composition of the seed crop and decisions about orchard roguing and improved seed orchard establishment. In this paper, a primary Chinese pine seed orchard with 49 clones is investigated for stability, variation and correlation analysis of factors which influence genetic quality of the seed lots from initial seed harvest to the stable seed production over a 12 years span. Results indicated that the reproductive synchrony index of pollen shedding has shown to be higher than that of the strobili receptivity, and both can be drastically influenced by the ambient climate factors. Reproductive synchrony index of the clones has certain relative stability and it could be used as an indication of the seed orchard status during maturity stage; clones in the studied orchard have shown extreme differences in terms of the gametic and genetic contribution to the seed crop at the orchard's early production phase specifically when they severe as either female or male parents. Those differences are closely related to clonal sex tendency at the time of orchard's initial reproduction. Clonal gamete contribution as male and female parent often has a negative correlation. Clone utilization as pollen, seed or both pollen and seed donors should consider the role it would play in the seed crop; due to numerous factors influencing on the mating system in seed orchards, clonal genetic contribution as male parent is uncertain, and it has major influence on the genetic composition in the seed orchard during the initial reproductive and seed production phase.     

Optimization of combined genetic gain and diversity for collection and deployment of seed orchard crops

Genetic gain and diversity of seed orchards’ crops are determined by the number of parents, their breeding values and relatedness, within-orchard pollination efficiency, and level of pollen contamination. These parameters can be manipulated at establishment by varying clonal representation (e.g., linear deployment), during orchard development by genetic thinning, or by selective harvesting. Since clonal fecundities are known to vary both within and among years, then each seed crop has a unique genetic composition and, therefore, crops should be treated on a yearly basis. Here we present an optimization protocol that maximizes crop’s genetic gain at any desired genetic diversity through the selection of a subset of the crop that meets both parameters. The genetic gain is maximized within the biological limit set by each clone’s seed-cone production and effective population size is used as a proxy to genetic diversity whereby any relationship among clones is considered. The optimization was illustrated using 3 years’ reproductive output data from a first-generation western larch seed orchard and was tested under various scenarios including actual male and female reproductive output and male reproductive output assumed to be either equal to that of female or a function of clonal representation. Furthermore, various levels of co-ancestry were assigned to the orchard’s clones in supplementary simulations. Following the optimization, all solutions were effective in creating custom seedlots with different gain and diversity levels and provided the means to estimate the genetic properties of composite seedlots encompassing the remaining “unused” seed from a number of years.     

Mating dynamics of Scots pine in isolation tents

Seed orchards are forest tree production populations for supplying the forest industry with consistent and abundant seed crops of superior genetic quality. However, genetic quality can be severely affected by non-random mating among parents and the occurrence of background pollination. This study analyzed mating structure and background pollination in six large isolation tents established in a clonal Scots pine seed orchard in northern Sweden. The isolation tents were intended to form a physical barrier against background pollen and induce earlier flowering relative to the surrounding trees. We scored flowering phenology inside and outside the tents and tracked airborne pollen density inside and outside the seed orchard in three consecutive pollination seasons. We genotyped 5683 offspring collected from the tents and open controls using nine microsatellite loci, and assigned paternity using simple exclusion method. We found that tent trees shed pollen and exhibited maximum female receptivity approximately 1 week earlier than trees in open control. The majority of matings in tents (78.3 %) occurred at distances within two trees apart (about 5 m). Self-fertilization was relatively high (average 21.8 %) in tents without supplemental pollination (SP), but it was substantially reduced in tents with SP (average 7.7 %). Pollen contamination was low in open controls (4.8–7.1 %), and all tents remained entirely free of foreign pollen. Our study demonstrates that tent isolation is effective in blocking pollen immigration and in manipulating flowering phenology. When complimented with supplemental pollination, it could become a useful seed orchard management practice to optimize the gain and diversity of seed orchard crops.     

林木种子园花粉污染与防治措施

林木种子园花粉污染是影响种子园种子遗传品质的重要因子,由于野生同种花粉进入种子园而增加遗传损失。本文综述了国内外林木种子园花粉污染研究的概况、污染水平、影响污染水平的因子和减少污染的措施。研究表明：DNA分子标记在分析种子园交配动态和种子园管理效果方面非常有效（例如,cpDNA、RAPD和SSR）;种子园污染水平比预期的更高;花粉产量好像对污染水平没有影响;空间和生殖隔离也没有产生预期的效果。目前,人工辅助授粉和疏伐是减少花粉污染的两种有效措施。为了改善种子园林木的亲本平衡,人工处理技术的使用,例如：赤霉素A4/7处理技术和无性繁殖技术在种子园很受欢迎。污染程度其他方面的研究工作仍在继续,本文提到的基因流的研究。并对我国种子园花粉污染研究和花粉管理提出建议：当分析种子园花粉污染时,涉及到花粉基因型自然的（花粉扩散）、生理（开花时间）和花粉生活力等因素都应该被考虑。     

Interannual genetic heterogeneity of pollen pools accepted by Quercus salicina individuals

Since flowering often varies among years in wind-pollinated woody species, the genetic composition of pollen pools accepted by seed parents can differ between years. The interannual heterogeneity of pollen flow may be important for maintaining genetic diversity within populations because it can increase genetic variation within populations and the effective sizes of the populations. In this study we examined heterogeneity, using paternity analysis and analysis of molecular variance, in the genetic composition of pollen pools among different reproductive years for six Quercus salicina seed parents in an 11.56-ha plot in a temperate old-growth evergreen broadleaved forest. The genotypes at seven microsatellite loci were determined for 111 adult trees and 777 offspring of the six seed parents in 2-5 reproductive years. Genetic differentiation of pollen pools among different reproductive years for each seed parent was significant over all seed parents and for each of four seed parents that were analysed for more than 2 years, but not for either of the other two seed parents (analysed for 2 years). For both the pollen pools originating from inside the plot and those originating from outside it, genetic differentiation among different reproductive years for each seed parent was significant over all seed parents. However, among-year genetic differentiation in the pollen pools originating from within the plot was detected for all four of the seed parents that were analysed for more than 2 years, but for only one of the four in the pools originating from outside the plot. Genetic diversity (estimated as allelic richness and gene diversity) was higher for pollen pools over all reproductive years than for pollen pools in single years. These results indicate that the year-to-year genetic variation of pollen pools increases genetic diversity in offspring and is strongly affected by the variation in pollen parents within the plot because of their high pollination contributions. The high year-to-year variation in pollen parents within the plot and overall supports the hypothesis that the offspring produced across years represent a larger genetic neighbourhood.     

Randomized,replicated, staggered clonal-row (R2SCR) seed orchard design

Spatial randomization of clones across a seed orchard’s grid is commonly applied to promote cross-fertilization and minimize selfing. The high selection differential attained from advanced-generation breeding programs sets high premier on the genetic gain and diversity delivery from seed orchards, thus clonal allocation is important and even more challenging when clones share common ancestry. Evidences of low selfing in many conifers’ seed orchards, as a result of their high genetic load, inbreeding depression, and polyembryony are abundant and call for orchards’ design re-evaluation, specifically when randomization is associated with added managerial burden. Clonal-rows represent a viable option for simplifying orchards management; however, they are often associated with elevated correlated matings between adjacent clones. Here, we propose a modified clonal-row design that replicates, staggers, and randomizes the rows, thus doubling the number of adjacent clones and providing different set of neighboring clones at each replication, thus allowing accommodating related parents more readily than any single-tree arrangement. We present a novel algorithm packaged in user-friendly software for executing various seed orchards’ designs. The developed program is interactive and suitable for any orchard size and configuration, accommodates any number of clones that are allocated to rows with variable length (ranging from a single tree to any even number) and pre-set separation zone between ramets of the same clone. The program offers three deployment modes (equal, linear, and custom) each with multiple layouts determined by the number of iterations requested. The resulting layouts are ranked based on four criteria including: (1) the number of empty positions, (2) deviation between expected and observed clone size, (3) minimum inbreeding, and (4) a neighborhood index that expresses the efficiency of clonal distribution.     

Gene flow and mating system in five <Emphasis Type="Italic">Cryptomeria japonica</Emphasis> D. Don seed orchards as revealed by analysis of microsatellite markers

We investigated gene flow in five Cryptomeria japonica D. Don seed orchards of two different types (common and miniature) at widely spaced locations using microsatellite markers. The quality of a seed crop is determined by many factors, including pollen contamination from outside sources, self-fertilization, and the proportion of contributions from constituent clones. Contamination rates were found to vary among ramets both within seed orchards (10.0–76.7% in the most variable seed orchard) and among seed orchards (35.0–65.8% on average). Among ramets, there were significant negative correlations between pollen contamination rate and their distance from the orchard edge; among seed orchards, there were significant positive correlations between the pollen contamination rate and the C. japonica forest area nearby. Some proportion of the pollen (10.7% of total contamination) also migrated from parts of the orchards that had not been treated with gibberellin to induce flowering. Self-fertilization rates varied among seed orchards (1.4–4.4% on average), and there were significant positive correlations between self-fertilization rate and the number of ramets per clone in both types of seed orchard. Contributions as pollen donors differed significantly among clones in all seed orchards. The distance between planted ramets, flowering phenology, and relative pollen fecundity may also have contributed to observed differences in paternal contribution. The influence of these factors on genetic potential did not differ greatly between the two types of orchards. This work was supported by grants from the Pioneer Special Studies Program of the Japanese Ministry of Agriculture, Fishery, and Forestry; the Program for Promotion of Basic Research Activities for Innovative Biosciences; and research fellowships from the Japan Society for the Promotion of Science for Young Scientists.     

Differential male reproductive success in Douglas fir

Summary Differential male reproductive success was studied in clones at two seed orchards of Douglas fir, Pseudotsuga menziesii (Mirb.) Franco. The performance of tester pollen parents was compared in controlled pollinations with two-parent pollen mixes. Marker pollen homozygous for a rare IDH allele was the genetic marker in each pollen mix. The resulting seeds were analyzed electrophoretically. At both seed orchards, the proportion of seeds sired by tester pollen significantly varied among the tester pollen parents. Tester pollen parents did not perform the same across all seed parents. The significant interaction effect was evidence of male-female complementarity. These results suggest a genetic basis to differential male reproductive success in Douglas fir.     

Effects of male fecundity, interindividual distance and anisotropic pollen dispersal on mating success in a Scots pine (Pinus sylvestris) seed orchard

Quantifying the effect of pollen dispersal and flowering traits on mating success is essential for understanding evolutionary responses to changing environments and establishing strategies for forest tree breeding. This study examined, quantitatively, the effects of male fecundity, interindividual distance and anisotropic pollen dispersal on the mating success of Scots pine (Pinus sylvestris), utilizing a well-mapped Scots pine seed orchard. Paternity analysis of 1021 seeds sampled from 87 trees representing 28 clones showed that 53% of the seeds had at least one potential pollen parent within the orchard. Pronounced variation in paternal contribution was observed among clones. Variations in pollen production explained up to 78% of the variation in mating success, which was 11.2 times greater for clones producing the largest amount of pollen than for clones producing the least pollen. Mating success also varied with intertree distance and direction, which explained up to 28% of the variance. Fertilization between neighboring trees 2.3 m apart was 2.4 times more frequent than between trees 4.6 m apart, and up to 12.4 times higher for trees downwind of the presumed prevailing wind direction than for upwind trees. The effective number of pollen donors recorded in the seed orchard (12.2) was smaller than the theoretical expectation (19.7). Based on the empirical observations, a mating model that best describes the gene dispersal pattern in clonal seed orchards was constructed.     

Genetic diversity in a seed production population vs. natural populations of Sitka Spruce

Isozyme analysis was applied to estimate the level of variation and the genetic structure of a seed-production population (i.e., seed orchard) and 10 range-wide natural populations of Sitka spruce (Picea sitchensis (Bong.) Carr.). Gene diversity and heterozygosity estimates were comparatively high in both the seed orchard and the natural populations studied. The seed orchard population showed a significantly higher number of alleles per locus and percentage of polymorphic loci. Though not significant, mean heterozygosity of the seed orchard was higher than that observed for all natural populations. Genetic distance analysis indicated that the seed-orchard population was genetically similar to three natural populations from which the parent trees were selected. Parent trees sampling breadth has been identified as the major cause for the observed increased level. The impact of recurrent selection and seed orchard biology and management on maintaining the genetic diversity is discussed.     

Variation in Male Fertilities and Pairwise Mating Probabilities in Picea glauca

Frequencies of multilocus male gametes in seeds collected from clones in several blocks of a white spruce seed orchard were analyzed as part of a 2-yr study of mating system variation in this species. Observed frequencies of male gamete types departed significantly from those expected assuming equal male fertilities among clones. Male gamete frequencies in seed crops were significantly heterogeneous among clones within blocks, and among blocks within clones. Clonal male fertilities were estimated from male gamete frequency data. These estimates were highly skewed, with a small proportion of the clones contributing male gametes to the majority of the seed. The estimates were significantly heterogeneous among clones within blocks, and among blocks within clones. Between-year variation in clonal male fertilities was also pronounced, with male fertilities of some clones changing by as much as three orders of magnitude. Clonal male fertility was significantly correlated with clonal male cone production in both years. These results are important with regard to assumptions made for the estimation of general combining ability, average genetic correlation among progeny from single parents, and expected response to selection in open-pollinated plant populations.     

Leaf-rust resistance in rye (<Emphasis Type="Italic">Secale cereale</Emphasis> L.). 2. Genetic analysis and mapping of resistance genes <Emphasis Type="Italic">Pr3</Emphasis>, <Emphasis Type="Italic">Pr4</Emphasis>, and <Emphasis Type="Italic">Pr5</Emphasis>

The conventional way to drive modifications in old forest tree seed orchards is to establish progeny trials involving each parent tree and then evaluate its contribution to the performance of the progeny by estimating its general and specific combining ability (GCA and SCA). In this work, we successfully applied an alternative parent selection tactic based on paternity testing of superior offspring derived from a hybrid seed orchard established with a single Eucalyptus grandis seed parents and six E. urophylla pollen parents. A battery of 14 microsatellite markers was used to carry out parentage tests of 256 progeny individuals including two independent samples of selected trees and one control unselected sample, all derived from 6-year-old forest stands in eastern Brazil. Paternity determination was carried out for all progeny individuals by a sequential paternity exclusion procedure. Exclusion was declared only when the obligatory paternal allele in the progeny tree was not present in the alleged parent tree for at least four independent markers to avoid false exclusions due to mutation or null alleles. After maternity checks to identify seed mixtures and selfed individuals, the paternity tests revealed that approximately 29% of the offspring was sired by pollen parents outside the orchard. No selfed progeny were found in the selected samples. Three pollen parents were found to have sired essentially all of the offspring in the samples of selected and non-selected progeny individuals. One of these three parents sired significantly more selected progeny than unselected ones (P0.0002 in a Fisher exact test). Based on these results, low-reproductive-successful parents were culled from the orchard, and management procedures were adopted to minimize external pollen contamination. A significant difference (P<0.01) in mean annual increment was observed between forest stands produced with seed from the orchard before and after selection of parents and revitalization of the orchard. An average realized gain of 24.3% in volume growth was obtained from the selection of parents as measured in forest stands at age 2–4 years. The marker-assisted tree-breeding tactic presented herein efficiently identified top parents in a seed orchard and resulted in an improved seed variety. It should be applicable for rapidly improving the output quality of seed orchards, especially when an emergency demand for improved seed is faced by the breeder.Communicated by D.B. Neale     

Simultaneous estimation of pollen contamination and pollen fertilities of individual trees in conifer seed orchards using multilocus genetic data

Seed orchards of forest trees are established to produce genetically-improved seed for reforestation. Genetic efficiency requires seed orchards to be (1) reproductively isolated form surrounding trees, (2) that there be similar fertilities among all orchard trees, and (3) minimum inbreeding. Each aspect of seed orchard reproduction can be simultaneously estimated using the observed frequency of each multilocus gametic type contributed through fertilizing pollen and the expected multilocus gametic segregation frequencies of orchard tree and of the contaminating population. These genetic estimates are directly relevant to the genetics of the tree breeding program. The flexibility of sampling seed — the basic data for these techniques — allows great scope for hypothesis testing, including tests of the accuracy of predictions of biophysical models of pollen movement. A simple example and a white spruce seed orchard case study are presented to illustrate the estimation technique and to investigate its sensitivity.     

Changes in growth performance and fecundity of Eucalyptus camaldulensis and E. tereticornis during domestication in southern India

Bulk seedlots of two unpedigreed multiprovenance seed production areas (SPAs) each of Eucalyptus camaldulensis and Eucalyptus tereticornis and one pedigreed seedling seed orchard (SSO) of E. tereticornis were planted in genetic gain trials at three southern Indian trial sites. At the time of seed collection, fewer than 30% trees flowered in these orchards, except in one E. camaldulensis SPA where 73% of the trees flowered, which had an estimated outcrossing rate of 86%. The E. tereticornis SSO was dominated by pollen from five highly fecund families of the Indian Mysore gum land race, which contributed 59% of the fruits produced. The SPA and SSO seedlots were compared with a bulked natural-provenance seedlot of E. camaldulensis (Morehead, Laura, and Kennedy Rivers, Queensland), another natural-provenance seedlot (Petford, Queensland), commercial eucalypt clones at two sites, and a Mysore gum seedlot at one site. At 3 years, progeny from all the four SPAs displayed good survival (79–93%) and performance similar to that of the natural provenances and the commercial clones. Progeny from the E. tereticornis SSO had significantly lower growth (at two sites) and lower survival at all three test sites. The Mysore gum seedlot displayed high fecundity and lower growth but better survival than the SSO progeny. Seed orchard genetic composition and flowering contributions thus affected progeny performance and the extent to which orchard genetic diversity was captured in the progeny. SPA progeny displayed greater fecundity than the natural provenances, indicating a response to selection for fertility.     

Considerations of correlated fertility between genders on genetic diversity: the Pinus densiflora seed orchard as a model

The correlation between 99 clone female and male fertilities in a first generation seed orchard of Pinus densiflora was studied over 6 years. The effective number of the parent (N_p) and the variance effective population number [N_e^(v)] were used to assess the impact of total (O_T), female (N_f) and male (N_m) fertility variation. A theoretical framework was developed to account for female and male fertility correlations as well as the impact of possible pollen contamination. Total fertility variation was described by the sibling coefficient (O_T: the probability that two genes randomly chosen from the gamete gene pool originate from the same parent), which was further subdivided into N_f and N_m. These parameters were compared under various conditions including the total seed harvest, imposing on equal seed harvest among the orchard's clones and two contamination scenarios (M = 0 and 20%). Fertility variations among females, males and clones were observed within and among years. Sibling coefficients (O_T) were lower, but the effective number of parent (N_p) and variance effective population number (N_e^(v)) were higher in years with moderate female and good male strobilus production. N_p for female and male reproductive outputs varied from 49 to 82 and from 57 to 93, respectively. N_p was higher for males than females. When the crop of the 6 years was pooled, N_p for female, male and the clone were 73, 87 and 85, respectively. The impact of female-male fertility correlation for conditions with no-, positive- and negative-correlations were assessed and their impact on O_T, N_p and N_e^(v) was also evaluated. It was demonstrated that the practice of equal seed harvesting from every clone, or the mixing of seeds from several years, would substantially improve the genetic diversity and the genetic representation of the seed orchard population when a positive correlation between gender fertilities was observed. The relevance of these results to supplemental-mass-pollination was discussed under two cases where equal- and un-equal amounts of pollen from clones were included in the pollen mixes.     

Effects of inbreeding on coastal Douglas fir growth and yield in operational plantations: a model-based approach

In advanced generation seed orchards, tradeoffs exist between genetic gain obtained by selecting the best related individuals for seed orchard populations, and potential losses due to subsequent inbreeding between these individuals. Although inbreeding depression for growth rate is strong in most forest tree species at the individual tree level, the effect of a small proportion of inbreds in seed lots on final stand yield may be less important. The effects of inbreeding on wood production of mature stands cannot be assessed empirically in the short term, thus such effects were simulated for coastal Douglas fir [Pseudotsuga menziesii var. menziesii (Mirb.) Franco] using an individual-tree growth and yield model TASS (Tree and Stand Simulator). The simulations were based on seed set, nursery culling rates, and 10-year-old field test performance for trees resulting from crosses between unrelated individuals and for inbred trees produced through mating between half-sibs, full-sibs, parents and offspring and self-pollination. Results indicate that inclusion of a small proportion of related clones in seed orchards will have relatively low impacts on stand yields due to low probability of related individuals mating, lower probability of producing acceptable seedlings from related matings than from unrelated matings, and a greater probability of competition-induced mortality for slower growing inbred individuals than for outcrossed trees. Thus, competition reduces the losses expected due to inbreeding depression at harvest, particularly on better sites with higher planting densities and longer rotations. Slightly higher breeding values for related clones than unrelated clones would offset or exceed the effects of inbreeding resulting from related matings. Concerns regarding the maintenance of genetic diversity are more likely to limit inclusion of related clones in orchards than inbreeding depression for final stand yield.Communicated by O. Savolainen     

Patterns of pollen flow in a dense population of the insect-pollinated canopy tree species Castanopsis sieboldii

Insect pollinations of tree species with high-density populations have rarely been studied. Since the density of adults can affect effective pollen dispersal, short-distance pollination, even by insects, may frequently occur in high-density populations. To test this prediction, we investigated pollination patterns in a high-density population of the insect-pollinated canopy tree species Castanopsis sieboldii by paternity analysis using genotypes at 8 microsatellite loci of 145 adult trees and 439 seeds from 11 seed parents in a 4-ha plot. We then explored their genetic effects on the population by calculating other population genetics parameters. Although C. sieboldii has high potential for long-distance dispersal of pollen (as indicated by a fat-tailed dispersal kernel), the cumulative pollination at the local scale was spatially limited and strongly dependent on the distance between parents due to the high density of adults. Genetic diversity estimates for pollen pools accepted by each seed parent converged on a maximum as the effective number of pollen parents increased. The genetic diversity of pollen pool bulked over all the seed parents from inside the plot did not differ from that of the total pollen pools. Therefore, although pollen flow from distant pollen parents may help to maintain the genetic diversity of offspring, pollen parents neighboring seed parents may be the main contributors to the genetic diversity of the offspring at the seed stage.     

Levels of genetic diversity at different stages of the domestication cycle of interior spruce in British Columbia

Concerns over the reductionist nature of the domestication of forest-tree species focus on the possibility of potential genetic erosion during this process. To address these concerns, genetic diversity assessments in a breeding zone the Province of British Columbia “interior” spruce (Picea glauca×engelmanni) program was conducted using allozyme markers. Genetic-variation comparisons were made between natural and production (seed orchard) populations as well as seed and seedling crops produced from the same breeding zone’s seed orchard. The natural population sample consisted of a total of 360 trees representing three stands within each of three watersheds present in the Shuswap-Adams low-elevation zone of interior British Columbia. Small amounts of genetic differentiation were observed among the nine natural populations (4%) and this was attributable to extensive gene flow Consequently, the sum of these nine populations was considered as a baseline for the genetic variation present in the breeding zone. The comparisons between the seed orchard and the breeding zone produced a similar percentage of polymorphic loci while the expected hetrozygosity (0.207 vs 0.210) and the average number of alleles per locus (2.7 vs 2.4) were slightly lower in the seed orchard. A total of seven natural populations’ rare alleles were not present in the orchard population, while one allele was unique to the orchard. The %P increased to 70.6% in the seedlot, but dropped to the natural populations level (64.7%) in the plantation. The observed increase in %P was a result of pollen contamination in the orchard. It is suspected that the reduction in the plantation was caused by an unintentional selection in the nursery. Simulated roguing in the orchard did not drastically reduce even if up to 50% of the orchard’s clones were rogued. However, roguing was associated with a reduction in the average number of alleles per locus (i.e., sampling effect). Received: 2 January 1996 / Accepted: 24 May 1996     

Effects of temperature and pollination site on pollen performance in Betula pendula Roth – evidence for genotype-environment interactions

We studied whether the differences between genetically different pollen donors (Betula pendula Roth clones) with respect to pollen-tube growth rate were consistent under different thermal conditions during pollen germination in vivo and in vitro. We conducted a single-donor hand-pollination experiment with same pollen donors and recipients in a plastic house seed orchard and at an outdoor clone collection. The prevailing daily mean temperature during pollen germination was 13°C higher in the plastic house than outdoors. The pollen-tube growth rate of each pollen donor was additionally determined in vitro on agar medium at five temperatures (10°, 15°, 22°, 30° and 35°C). A significant interaction between paternal clone and pollination site as well as between paternal clone and temperature was found, which provides evidence for genotype-environment interactions. Genotype-environment interactions can have evolutionary significance in maintaining the variation in pollen-tube growth rates. At seed orchards, genotype-environment interactions can cause deviations from the expected genetic composition of the seed crop depending on the prevailing environmental conditions during pollen-tube growth. Received: 24 September 1999 / Accepted: 29 September 1999     

Estimation of gene flow into two seed orchards of loblolly pine (Pinus taeda L.)

Summary Multilocus allozyme markers, which were present in background stands but not in two seed orchards, enabled estimation of gene flow into two seed orchards of loblolly pine. Estimates averaged 36% in two orchards over three years. When pollen pool frequencies in the background stands were used rather than gene frequencies in the non-orchard trees, the estimates averaged 60%. In one year, trees in the row on the edge of one orchard received significantly more pollen from background stands. Estimates of gene flow between the two 2-ha orchards average 10%. Implications of the observed levels of gene flow are discussed in terms of population genetics and seed orchard management.Scientific Contribution No. 1285 from the New Hampshire Agricultural Experiment Station. This work was part of McIntire-Stennis Project 11 Allozyme studies of coniferous forest tree populations