Background Pollination Research Articles

Modern breeding methods in forestry aimed at preserving genetic diversity

This research is devoted to analysing the impact of modern breeding measures in forestry on the level of genetic diversity of forest tree species. It has been found that the main source of improved seed material for the genetic restoration of forests is base forest seed orchards. Aspects of the influence of determining factors – background pollination and the number of clones – on the indicators of genetic variability of progeny have been analysed in detail. The potential of background pollination in forest seed orchards in the context of a significant decrease in the effectiveness of breeding measures and a parallel increase in the level of genetic variability of progeny has been studied. An analysis of data on the minimum number of clones in seed orchards has been carried out based on the practical experience of other developed countries. The dynamics of clone variability in terms of fertility have been investigated. The potential impact of clonal selection on the genetic diversity of tree species, particularly in reducing it, has been identified. It has been confirmed that integrating the concept of family forestry, which involves the use of vegetative propagation techniques, into the breeding strategy significantly increases the level of genetic variability in progeny. The study has demonstrated that the multiple-population breeding system provides the optimal preconditions for synergising the process of long-term intensive breeding and preserving the gene pool of tree species. It has been determined that there is no negative impact on genetic diversity from implementing a complex of optimally planned breeding programs. At the same time, the potential for intensifying the quality of gene pool conservation in the process of forest ecosystem restoration through the use of improved seed material and clones in artificial orchards has been established. Special attention is given to the maintenance of ex situ – valuable genetic material in forest seed production facilities, including forest seed orchards, trial cultures, and clone archives of plus trees. Research has shown that the implementation of modern innovative solutions and scientific recommendations can minimise the loss of genetic diversity in forest tree species. The results can be applied in contemporary forestry breeding programs

Лесная селекция и генетическое разнообразие древесных пород

In scientific literature there are different views on the connection between forest tree breeding and genetic variability of wood species. This article has aimed to review the current Russian and foreign literary sources on the impact of breeding measures on the level of genetic diversity of forest wood species. Maintaining adequate genetic variability is necessary for adaptation to the environmental changes, as well as for long-term breeding. As soon as seed plantations are the source of improved seeds for forest regeneration, the influence of such factors as the number of clones and background pollination on the level of genetic variability of the progeny has been considered in detail. The data on the minimal clone number in seed plantations in different countries has been presented and the variability of the clones based on their fertility has been discussed. The importance of background pollination in seed plantations has been highlighted as soon as, on the one hand, it reduces the effect of breeding, but on the other hand, it increases the level of genetic variability of the progeny. A decline in genetic diversity of wood species can be caused by clone selection (which is the basis for clonal forestry). However the analysis of literary sources has shown that the reduction in genetic diversity is minimal if scientific recommendations are fulfilled. The use of the seeds from controlled cross-breeding of plus trees selected as a result of genetic evaluation (the so-called family forestry with vegetative propagation) in the somatic embryogenesis of the common spruce increases the level of genetic variability of the progeny. It has been shown that the multiple population breeding system allows to combine intensive long-term breeding and genetic conservation of wood species. The conclusion has been drawn that the implementation of optimally planned wood species breeding programs does not lead to significant narrowing of genetic diversity. On the contrary, forest tree breeding contributes to the preservation of a better gene pool, transmitting it in the process of forest regeneration through improved seeds and clones into homogeneous stands. Moreover, the objects of forest seed growing such as the archives of plus tree clones and forest seed plantations, as well as test cultures contain valuable genetic material ex situ.

Moths as potential pollinators in avocado (Persea americana) orchards in temperate regions

ABSTRACT Avocado (Persea americana) flowers are primarily diurnal, however low minimum overnight temperatures can delay in the opening of female-phase flowers such that the flowers open late in the day and remain open overnight. To determine whether moths are important visitors to avocado flowers at night, we trapped moths in the Bay of Plenty, New Zealand, and examined the pollen moths carried. 11.5% of moths carried avocado pollen grains, and 50.4% of all moths were found to carry pollen grains from other plant species. Moth species diversity was highly variable between orchards, but Ichneutica mutans, Ichneutica ustistriga, Epyaxa rosearia, Rhapsa scotosialis, Phrissogonus laticostatus were observed at all sites and Ichneutica steropastis at three sites, with avocado pollen grains found on 10%–33% of these individual species. We suggest that these species may be the most important pollinating moth species because of their abundance, proportion of individuals carrying avocado pollen, and the number of pollen grains per individual. This exploratory study has shown that moths are capable of carrying avocado pollen grains and may be providing a background pollination service to complement that of honey bees (Apis mellifera). To better understand moth contribution to pollination, fruit set needs to be assessed.

Patterns of Effective Pollen Dispersal in Larch: Linking Levels of Background Pollination with Pollen Dispersal Kernels

Monitoring patterns of mating and pollen dispersal in forest tree populations subjected to nature conservation is essential to understanding the dynamics of their reproductive processes and might be helpful in making management decisions aimed at conserving genetic diversity and integrity over the long term. However, little is known about effective pollen dispersal in natural populations of conifers, particularly in subdominant species such as larch. We investigated patterns of pollen dispersal in the Polish larch population of Świętokrzyski National Park. The studied population was located on Chełmowa Mountain in a forest complex 160 ha in size, which is relatively isolated from other forest stands. We assessed if local pollen dispersal inferred from pollen dispersal kernels could provide indications of the level of background pollination from sources located outside of the forest complex. The analysis focused on two plots, each encompassing 126 adult trees, and seed samples (n = 600) collected from 20 trees. Using 11 nuclear microsatellites and spatially explicit mating models, we identified details of mating patterns. The rate of self-fertilization was low (0.0268). Background pollination was moderate (0.4058), and the mean pollen dispersal was found to be 167 m and 111 m, based on exponential-power and Weibull dispersal kernels, respectively. Specific simulations performed based on the estimated pollen dispersal kernels provided background pollination levels comparable to those observed for real data, suggesting that the pollen contributing to background pollination likely originated from the studied forest complex and not from other surrounding populations. These results confirm the high potential for maintaining the genetic integrity of the larch population and support efforts aimed at promoting regeneration of the stands, either natural or through the artificial planting of seedlings derived from trees growing in the core larch population of the protected area.

Gene flow of common ash (Fraxinus excelsior L.) in a fragmented landscape.

Gene flow dynamics of common ash (Fraxinus excelsior L.) is affected by several human activities in Central Europe, including habitat fragmentation, agroforestry expansion, controlled and uncontrolled transfer of reproductive material, and a recently introduced emerging infectious disease, ash dieback, caused by Hymenoscyphus fraxineus. Habitat fragmentation may alter genetic connectivity and effective population size, leading to loss of genetic diversity and increased inbreeding in ash populations. Gene flow from cultivated trees in landscapes close to their native counterparts may also influence the adaptability of future generations. The devastating effects of ash dieback have already been observed in both natural and managed populations in continental Europe. However, potential long-term effects of genetic bottlenecks depend on gene flow across fragmented landscapes. For this reason, we studied the genetic connectivity of ash trees in an isolated forest patch of a fragmented landscape in Rösenbeck, Germany. We applied two approaches to parentage analysis to estimate gene flow patterns at the study site. We specifically investigated the presence of background pollination at the landscape level and the degree of genetic isolation between native and cultivated trees. Local meteorological data was utilized to understand the effect of wind on the pollen and seed dispersal patterns. Gender information of the adult trees was considered for calculating the dispersal distances. We found that the majority of the studied seeds (55–64%) and seedlings (75–98%) in the forest patch were fathered and mothered by the trees within the same patch. However, we determined a considerable amount of pollen flow (26–45%) from outside of the study site, representing background pollination at the landscape level. Limited pollen flow was observed from neighbouring cultivated trees (2%). Both pollen and seeds were dispersed in all directions in accordance with the local wind directions. Whereas there was no positive correlation between pollen dispersal distance and wind speed, the correlation between seed dispersal distance and wind speed was significant (0.71, p < 0.001), indicating that strong wind favours long-distance dispersal of ash seeds. Finally, we discussed the implications of establishing gene conservation stands and the use of enrichment planting in the face of ash dieback.

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.

Scarcity of ecosystem services: an experimental manipulation of declining pollination rates and its economic consequences for agriculture.

Ecosystem services (ES) such as pollination are vital for the continuous supply of food to a growing human population, but the decline in populations of insect pollinators worldwide poses a threat to food and nutritional security. Using a pollinator (honeybee) exclusion approach, we evaluated the impact of pollinator scarcity on production in four brassica fields, two producing hybrid seeds and two producing open-pollinated ones. There was a clear reduction in seed yield as pollination rates declined. Open-pollinated crops produced significantly higher yields than did the hybrid ones at all pollination rates. The hybrid crops required at least 0.50 of background pollination rates to achieve maximum yield, whereas in open-pollinated crops, 0.25 pollination rates were necessary for maximum yield. The total estimated economic value of pollination services provided by honeybees to the agricultural industry in New Zealand is NZD $1.96 billion annually. This study indicates that loss of pollination services can result in significant declines in production and have serious implications for the market economy in New Zealand. Depending on the extent of honeybee population decline, and assuming that results in declining pollination services, the estimated economic loss to New Zealand agriculture could be in the range of NZD $295–728 million annually.

Genetic variation of pedunculate oak (Quercus robur L.) in the urban woodlands of Helsinki

ABSTRACTWe present a genetic profile of pedunculate oak (Quercus robur L.) in three woodlands of the Helsinki region. We genotyped all mature trees and samples of seedlings to evaluate patterns of genetic variation and gene flow, and evaluate the long-term stability and natural regeneration of these stands. Although five microsatellite loci showed no significant differences in heterozygosity between generations in most locations, significant (p < .05) pairwise differences were observed between mature trees and seedlings at Seurasaari, with higher diversity within seedlings. Ninety-four percent of the genetic variation occurred within sample sites. Background pollination contributed up to 61% of the diversity among seedlings, and thereby plays an important role in shaping the genetic variation and structure of future generations. Results indicate that pedunculate oak trees in the surveyed parks of Helsinki belong to the same population and that the urban environment per se does not interfere with gene flow over the distances represented here. Based on our findings, a minimal-maintenance program reliant upon natural regeneration of oak in the public parks of Helsinki seems plausible.

Inter-year variation in selfing, background pollination, and paternal contribution in a Norway spruce clonal seed orchard

We aimed to investigate inter-year variability in mating system and paternity in an experimental Norway spruce (Picea abies (L.) Karst.) clonal seed orchard that was established with five geographically distinct populations. Using five nuclear microsatellite markers, we analysed 1396 progeny of five mother trees representing each of the populations in three successive mast-years. Selfing varied among mother trees, ranging from 0% to 18.3% with a mean of 13.9% in 1994, 10.1% in 2004, and 7.6% in 2006. Considerable background pollination was observed in each of the three studied mast-years and reached ca. 58%. The paternity assignment conducted showed an uneven male contribution to the seed crop, what was partly related to the number of ramets per paternal clone. All provenances contributed to the seed crop, but with different input, and two provenances dominated. Effective pollen dispersal was significantly determined by distance, with 72.2% of the seed crop resulting from crosses at a distance of up to 15 m. Our study indicated that despite considerable differences in the geographic origin of populations, inter-mating between clones from each population was possible, which generally agrees with the expectations related to the establishment of this seed orchard.

Chloroplast DNA variation and pollen contamination in a Pinus brutia Ten. clonal seed orchard: implication for progeny performance in plantations

Pollen contamination is one of the important factors affecting the yield, adaptability, and genetic quality of the seed produced from seed orchards in forest tree breeding programs. Incoming pollen from the forests surrounding the seed orchard is a major concern in tree breeding because it contributes to losses in the expected genetic gains from seed orchard crops. The genetic variation and the level of pollen contamination in a 16-year-old Pinus brutia Ten. first-generation clonal seed orchard was studied using chloroplast microsatellite markers (cpSSRs). In total, 23 alleles and 36 unique allelic combinations (haplotypes) were detected based on the 6 cpSSR loci analyzed. The haplotypic diversity of the clones in the seed orchard was found to be 0.849. Out of 300 embryos analyzed, 87 were not compatible with any male parent within the seed orchard. Thus, 29% of the embryos were sired by pollen sources outside the orchard (i.e. apparent contamination). Microsatellite-based analysis revealed that the estimated contamination rate was 39.3%. Background pollination at this level will cause losses of 20% in the expected genetic gains. Our findings are valuable for the assessment of the intended seed orchard function, i.e. provision of genetically improved seed. It may be worthwhile to use pollen management strategies like strobilus stimulation, controlled pollination, and supplemental mass pollination to decrease pollen contamination and increase the genetic quality of the seeds produced.

A double-threshold temperature sum model for predicting the flowering duration and relative intensity of Betula pendula and B. pubescens

The accurate prediction of the flowering period and the amount of released pollen of wind-pollinated trees is important for predicting the aerobiological pollen amounts and for estimating the intensity of background pollination of orchard seed production. Current phenological models, such as the commonly used temperature sum (thermal time) model, are efficient for predicting the timing of point events, e.g. the onset of flowering or leaf unfolding. However, the flowering period of boreal trees, including Betula pendula and B. pubescens, may last up to 5 weeks with widely varying flowering intensity. Therefore, the ability to predict the duration of the whole flowering period and the intensity of pollination is very important. In this paper, we present a new phenological model that predicts the whole flowering period and daily (normalized) variation of flowering intensity. The model is based on similar principles as the temperature sum model. The model was calibrated against pollen data recorded with pollen traps placed in several locations in Southern and Central Finland. Our new model predicted accurately the variation in the intensity throughout the flowering period. Moreover, it was able to predict the start and end of the pollination season with accuracy comparable to that achieved with an ordinary temperature sum model for point events. Due to limited amount of test data, the data-dependency of the model had to be tested with a bootstrapping approach. With this method, the model fit and parameter values showed to be independent of the parameter fitting data. The model can be used to predict the whole flowering period of wind-pollinated boreal trees for many different purposes, such as aerobiological forecasts of allergenic pollen, or generation of input data for models of long-range pollen transport.

Southern pollen sired more seeds than northern pollen in southern seed orchards established with northern clones of Pinus sylvestris

Contamination by southern pollen is a considerable problem in Scots pine (Pinus sylvestris L.) seed orchards established with northern clones. This study investigated whether the contamination was due to the competitive superiority of southern pollen by carrying out competition trials using mixtures of pollen from northern and southern populations of Scots pine. Trials were performed in a southerly seed orchard established with clones originating from northern populations. Seed paternity (siring) was determined through the analysis of allozyme variation. Southern genotypes sired significantly more seeds (76%) than their northern competitors and across all mixed-pollen crosses. Maternal genotype had no effect on seed siring success. The mean flower abortion rate was lower in southern pure-pollen crosses and mixed-pollen crosses than in northern pure-pollen crosses. The results show that local pollen may induce high levels of background pollination in southern seed orchards composed of northern genotype grafts. These results must be taken into account when aiming to produce suitable reforestation material for northern areas.

Genetic variation, mating patterns and gene flow in a Pinus pinaster Aiton clonal seed orchard

• Relatedness among parents, variation in clonal fertility and background pollination deviate the realized genetic gain and the gene diversity of open pollinated seed orchard from expectation, in particular in wind pollinated species such as Pinus pinaster Aiton. • This work investigates the genetic variation, the mating system and the pollen contamination in a P. pinaster clonal seed orchard (CSO), by screening the 60 clones from the CSO and the seeds collected from 21 mother-trees with three nuclear microsatellites. • The expected diversity was similar, but the observed heterozygosity decreased 20% in the progenies compared with the parental trees. The outcrossing rate was 90.1%, the biparental inbreeding 21.7% computed through a multilocus approach, and the observed selfing 3.9%. The observed gene flow from outside the CSO was 52.4%. • From the results we concluded that the observed gene flow and the biparental inbreeding were high, and care should be taken in the implementation and management of future CSO, in particular clones should be checked for relatedness and the ramet number could be directly proportional to their breeding value.

Flowering and Airborne Pollen Occurrence in a Pinus sylvestris Seed Orchard Consisting of Northern Clones

To explain the high background pollination rate detected in earlier studies, this study investigated the flowering phenology of a Scots pine seed orchard with respect to airborne pollen occurrence during 1992 and 1993. The receptive period of the female strobili and the shedding period of the male strobili were observed visually. Airborne pollen was monitored with Rotorod traps located inside and outside the seed orchard. There was no time gap in the onset of flowering between the earliest female and male strobili in 1992. Female flowering began 3 days earlier than male flowering in 1993, and the earliest strobili were probably pollinated by pollen transported long distance from more southerly areas. The almost simultaneous peak in pollen occurrence inside the seed orchard and in surrounding pine stands indicates that the seed orchard clones are not temporally isolated from sources of contamination. However, pollen concentrations inside the seed orchard were higher than those in the surrounding stands. Therefore, flowering phenology cannot sufficiently explain the observed pollen contamination rates in this seed orchard.

Effect of southern pollination on the survival and growth of seed orchard progenies of northern Scots pine ( Pinus sylvestris) clones

The growth and survival of background pollinated progeny of northern Scots pine clones from seed orchard located in southern Finland was examined at an age of 10–15 years and compared with the respective performance of seedlings from local natural stands. The material consisted of 33 progeny tests located in northern Finland within the original areas of the clones. Although no clear difference was observed between the height growth of the two groups, the survival was significantly lower in the seed orchard material (35%) than in the local stand material (56%). The relative survival (seed orchard vs. local entries) decreased steadily along with the decrease in the effective temperature sum of the trial sites, and was relatively small in the northernmost trials. The results indicate that the totally background pollinated seed from southwards-transferred, young seed orchards even can be used for reforestation in southern and central Lapland, at least in areas located at relatively low altitudes. The decrease in background pollination levels owing to the ageing of these orchards will increase the potential use of this seed. Using only those orchards containing the northernmost clones, combined with selective harvesting of the most hardy portion of the clones, is proposed as a means of further improving the adaptedness of planting material for northern conditions.

Background pollination in Pinus sylvestris seed orchards

The proportion of background pollen grains in the seed crops of two Pinus sylvestris seed orchards in Central Finland was estimated with the aid of multilocus allozyme markers. The orchards studied were more than 30 years old and in full pollen production. For the bulked seed crops of the seed orchard with southern clones the estimated average of background pollination over four years was 26%. There were statistically significant differences between years. No significant heterogeneity in the degree of background pollination between clones was found. Among single ramets there was significant heterogeneity in the estimated contamination rates, but the variation was not related to position in the orchard. For the seed orchard with northern clones the bulked seed crop was studied only for one year and the level of background pollination was found to be 33 %. These estimates are fairly high, but lower than for many other orchards. Background pollination at this level will cause losses in expected genetic gains...

Long geographic transfers, a possible way of eliminating pollen contamination in advanced-generation seed orchards of Pinus sylvestris

A new generation of seed orchards will be established during the next few years. All means of achieving a higher genetic level in future seed orchards must be used. Progeny testing is under way in many countries and subsequent recurrent selection will be done for advanced-generation seed orchards. Since the new seed orchards will be more genetically differentiated than the old ones, the effect of pollen contamination will be more harmful; therefore serious efforts should be made to eliminate undesirable pollen contamination. Location of the orchards to the south of the utilization area of the seed and continuous pine forests would almost completely eliminate pollen contamination. Difference in flowering times would be considerable, and above all, background pollination would be negligible. In addition, the time lag between selection and seed production would be essentially shorter. Optimal locations can be suggested with models of climatic adaptation and then checked with experimental plantations. Hazards caused by pests and diseases must be investigated and possible physiological after-effects of the new environment on the annual rhythm of the seedlings clarified. Despite these reservations, long-distance transfers of seed orchards are probably the only feasible way of avoiding pollen contamination in large-scale seed production projects.