Overview of Wu20 19 Clone Forestry Family Forestry

The application of asexual reproduction in forestry has a long history. This chapter summarizes the genetic advantages of clonal forestry compared with family forestry. Theoretical research and experimental data from offspring and cloning experiments show that the additional genetic gain (5-25%) obtained from cloning experiments and configurations is possible in conifers, effectively doubling the available genetic gain of family forestry in the same generation. There are three perceived risks of using clones in forestry: (1) the risk of planting failure; (2) The risk of biodiversity loss at forest and landscape level; (3) Risks related to the success rate of asexual reproduction (or SE). Three theoretical models are reviewed and described to evaluate risks and determine the number of clones needed to reduce these risks. All studies support that the number of "safe" clones is between 5 and 30. The genetic harvest and experience of individual species, especially conifers and eucalyptus, are reported. The combination of genome selection and somatic embryogenesis may accelerate the development of cloning forestry by shortening cloning experiments or completely omitting long-term cloning experiments.

Clone forestry; Genetic gain; Asexual reproduction; Risk; profit

The advantage of asexual propagation of Chinese fir in China was proved long ago (1500) (Huanglan 1988), and that of Chinese fir in Japan was proved 800 years ago (Hata 1974). Because the asexual propagation of these tree species is relatively easy, rooting and cutting are used to propagate excellent tree species with ideal characteristics. Local farmers usually don't see this risk or realize it, because they will plant quite small plots with rootstock cuttings. Poplar asexual propagation also has a long history in Europe. Organized clonal forestry began in the early 20th century, and single plantation has become a common form of land use in southern Europe. Although it has a long history, asexual reproduction and asexual reproduction of large-scale industrial plantations were only carried out on poplar, tropical and subtropical eucalyptus in 1970s and 1980s (Libby and Ahuia, 1993). At the same time, the risk of cloning forestry was generally recognized (Libby 1982).

The development and implementation of clonal forestry have been successful in some broad-leaved tree species, especially tropical and subtropical eucalyptus (Rezende et al. 20 13) and temperate popular tree species and willow (zsuffa et al. 1993), because they are relatively easy to carry out asexual propagation and short-term rotation cutting. At present, nearly 50% of eucalyptus forests in Brazil are clones. Through the combination of genetic improvement, afforestation improvement and asexual reproduction selection, the average productivity of eucalyptus plantation has increased from 25-30 cubic meters/hectare/year to 35-45 cubic meters/hectare/year. The productivity in some areas may exceed 60 cubic meters/hectare/year. Rezende et al. (20 13) and Griffin(20 14) recently summarized the benefits, risks and technical requirements of eucalyptus. We will mainly focus on conifers.

For conifers, before the development and adoption of SE (somatic embryogenesis), it is a great challenge for superior trees to reproduce asexually on a large scale due to maturity (Hakman et al.1985; Park 2002). The recent review of SE in European forestry shows that the use of cloned forestry in Europe mainly faces two challenges (Leluwater et al.2013): (1) cost; (2) Public acceptance. Although it is not an important factor at present, public acceptance may become very important if the long-term impact on genetic variation cannot be completely solved by using clonal forestry. In order to evaluate the cost of clonal forestry, it is necessary to prove a key genetic advantage, including using seedlings or asexual cuttings for growth and other traits compared with current family forestry. In order to obtain economic benefits, it is necessary to comprehensively evaluate the cost structure of using clones relative to family forestry by cash flow discount method. If this assessment can prove the economic advantages of using clonal forestry, then the corresponding analysis should address the potential risks of clonal deployment related to family forestry, including long-term planting survival rate and productivity, as well as ecological and social problems.

This risk analysis was carried out before developing SE for coniferous species. We will review and summarize the genetic gains (benefits), potential risks of clonal planting development, actual genetic gains and the number of clones deployed in several successful clonal forestry programs in the world.

For the distribution of Swedish forestry clones, the long-term genetic diversity at landscape, regional and species level is important, because Swedish forestry has not established pure artificial forests, but combined the regeneration of artificial forests with the mixed goals of production and protection. Therefore, it is very important to quantify clonal forestry relative to family forestry from the perspective of diversity.

With the progress of generations and the increase of selection intensity, the genetic benefits of tree improvement are also increasing. In the same generation, higher genetic gain is usually accompanied by the intensity of selection and reproduction methods. Genetic gain usually progresses as follows:

There are three perceived risks of using clones in forestry: (1) the risk of planting failure; (2) The risk of biodiversity loss at forest and landscape level; (3) Genetic acquisition risk related to reproductive success rate. The serious risk assessment of clonal planting materials begins with 1980, and the question is "how many clones are safe in each plantation" (Libby 1982). Risk is also related to genetic gain. A clone will get the greatest benefit, but also the greatest risk, while the mixed seedlings from natural forests will have no benefit, but the lowest risk. In order to balance these two factors, we must compromise.

Three theoretical bases were used to estimate the number of clones needed to reduce the risk: (1) single gene and planting failure risk method; (2) Genetic sampling theory, adaptive genetic diversity loss and genetic gain method; And (3) modeling and computer simulation of pest attack and genetic diversity.

By using single gene method, it has been proved that the probability of planting failure is very sensitive to gene action (dominant or recessive) and the frequency of toxic genes in diseases or pests (Roberts et al.1990; Roberds and Bisir, 2007). When 13 to 25 clones are used, there is little difference in failure probability between risk levels. In fact, the number of endless clones is quite consistent with the effective population size (ne=25 clones). It is important to realize that in most cases of forestry, we don't know what the future risk of unknown biological threats is for the genetic system that may threaten the stand in the future (that is, the gene function or gene frequency of resistance genes). The interesting result of this method is that including more than 20-40 clones will not provide any greater risk reduction (Bihir and Roberts 1995, 1997). One is the gene frequency of pest toxicity, the other is the gene frequency of tree resistance; When the threshold is reached, it is not safe to increase the asexual coefficient.

According to the theory of genetic sampling, loss of heterozygosity or additive genetic variation is a function of sewall wright ne, which can be described as1-(1(2ne)). The effective size of about 10 individuals provides 95% of the original genetic variation in the first generation population. Sewall wright of 20 can maintain about 80% variation after 10 generation (Roberds et al. 1990). In order to maintain the suitability of a single stand under Swedish conditions, it is suggested that two different requirements of stand vitality must be recognized: (1) the critical level of gene diversity; (2) Inhibit the diffusion of selective destructive factors and completely inhibit the critical number of genotypes. Use website resources. It is suggested that 25 clones should be used in a mixture, and the national effective number ns=4 indicates the minimum genetic diversity (Lindgren, 2008). This is similar to the genetic diversity of two infinitely complete sibling families, with four unrelated parents or a large half-sibling family, that is, one mother and infinitely many fathers. In the long-term breeding process, the clone mixture with Ns=4 maintained 87.5% of the original gene diversity.

The small loss of genetic variation is mainly due to the increase of homozygotes and the loss of low frequency alleles. Low-frequency alleles have little protective effect on wild populations, but they play an important role in protecting evolutionary potential. The protection of these low-frequency genes is an important part of the genetic protection plan, so with the implementation of large-scale clonal forestry, the management of non-clonal and natural forests is still very important.

The latest model of more complex resistance (multiple resistance affected by multiple genes) of future pests, which is known or unknown at present, provides important improvement and confirmation for the results of single gene model (Yanchuk et al., 2006). Even for different types of clonal mixtures (such as random mixing, mosaic of monoclonal blocks and clonal blocks), the results are consistent. About 18 genotype is close to an "optimal" or safe number to reduce the risk of some unknown future biological threats, although the difference between 6, 18 and 30 genotypes is relatively small. The author concludes that these data may be common enough for many species with no detailed information or those with long rotation age.

These three theoretical studies all point to the same general conclusion reached by Dr. Libby 30 years ago-increasing the number of genotypes beyond a certain number has little effect on reducing the risk of loss: 5-30 clones provide an infinite population (such as wild forest), and the optimal diversity level may exist around 18 effective genotypes, and the minimum value may be around 6.

Cloning forestry has the risk of genetic gain. Theoretically, only when 100% reproduction is achieved by cutting or somatic embryogenesis can the genetic gain calculated according to genetic parameters be obtained (Haynes and Wollaston, 199 1 year). With the decrease of reproductive success rate, the genetic gain of clones decreased. For example, if the success rate of breeding is 50% and the selection intensity is 1% (the best two trees are selected from a group of 200 trees), only 85% of the potential total additional gain can be obtained. Therefore, regardless of the growth, adaptation and wood properties of trees, they cannot be used as operational clones unless they can be economically propagated (Griffin, 20 14).

Estimating the genetic gain of clonal forestry is higher than that of family forestry, which is very important to evaluate the economic benefits of clonal forestry. The following are some examples of the general survey of several main plantation species in Sweden except Norwegian spruce.

New Zealand sells about 2.5-5 million clones of Pinus radiata every year. In 2008- 13, the total seedling market was 45.68 million, and about 4- 1 1% were clones. In Australia, about 20 million radial pines have been produced, most of which are branches rooted from donors' hedges. These branches were cultivated from elite full-sib families, and now hundreds of clones are being tested in the field (find et al. 20 14, Mike Carson 20 13, personal communication).

Cloned forestry is mainly promoted by two companies in New Zealand and Australia: Forest Genetics (www. Forest genetics.com) and Australian trees (www.arborgen.co.nz). The two companies produce about 20 new clones through field experiments every year. Forest genetics estimated that the genetic gain of the tested clones in the control pollination family was between 15-20%, the sound velocity (stiffness) was 25%, and the average wood density was 10- 15%. Compared with the control group, the clonal subset increased the resistance (leaf retention rate) to dothistroma by 40%.

In New Zealand, clones of Pinus radiata are sold in the form of rooting cuttings, and the price ranges from NZD 650-720 (SEK 3700-4200) per 1000 plants, compared with NZD 340-450 (SEK 1950-2600) for seedlings produced by CP. Preliminary economic analysis shows that the net present value (30 years, 8%) of improved clonal forestry seedlings of 2 180 NZD per hectare (SEK 12500) is about NZD 300 (SEK 1700) (Mike Carson, 201700).

According to a recent survey of three pine trees in the southeastern United States, about 843.5 million saplings (down from 654.38 billion before the recession in the first decade of this century) were planted by 32 cooperative members, of which 87. 1% were composed of loblolly pine. Educational cooperatives in the southeastern United States (McKeand et al. 20 15). About 95% of plantations are built with genetically modified materials. Most of the stands have OP families (84%), about 8% have specific hybrid or complete sibling families, and about 2% have experimental cloned varieties. Advanced seedling distribution can provide 40-60% more yield for specific families than unmodified loblolly pine. Crossing all sibling families has become an important part of loblolly pine regeneration. Since 2000, the annual output of full-sib seedlings has increased to 63.2 million in 20 13 years, and the total planting amount of full-sib seedlings has exceeded 325 million in the past 14 years (Steve McKeand, 20 14, personal communication). In a series of productivity and afforestation management systems, it is estimated that the net present value per hectare is 124 US dollars to 74/kloc-0 US dollars (1000-6000 Swedish kronor), which is used to plant the best genotype in family forestry (McKeand et al. 2003). The economic benefits of cloned forestry are rarely recorded. According to the catalogue data published by Arborgen, the net present value of a clonal variety (agv var) is about 3,346 US dollars per hectare (SEK 27,500). In contrast, according to their calculation, they got $2,865,438+09 (SEK 23,000) from deploying the best quality control pollination family (MCPE). The seedling price of cloned varieties is $320 per 1000 plants (SEK 2600), while that of MCPE (super seedlings in 2004-2005) is $205 per 1000 plants (SEK 1700).

Sitka, a Scottish spruce, is the main conifer in artificial forest. The Scottish Forestry Commission has long been interested in clonal propagation and clonal forestry (http://www.forestry.gov.uk/fr/ggae-548G6t), although there is no clonal forestry and experimental cloning to practice at present. For the new plantation, 75% of the seedlings come from open pollinated seed orchards, and 25% from full-sib families that control pollination. Rooting cuttings are used for asexual reproduction, that is, asexual reproduction of family forestry. It is estimated that about 8 million cuttings are deployed every year (Li Jiading, 20 15, personal communication). In Ireland, as many as 3 million cuttings come from plants in the southeast every year, that is, using the concepts of family forestry and plant propagation (Thompson, 20 13).

In British Columbia (https://www.for.gov.bc.ca/hre/forge/), conifer species have not been cloned, but several species have been cloned, including Chinese fir, hemlock and indoor spruce (Michael Stoehr 20 15, personal newsletter).

Clonal experiments of spruce and spruce were carried out in New Brunswick province, but clonal forestry has not been implemented in the canopy (Weng Yunhui, 20 15, personal communication). In the private sector, JD Irving Co., Ltd. has been active in the southeast since 1995, and is committed to producing a number of refrigeration and preliminary test production lines. The company tested more than 2000 varieties (clones) in field experiments, mainly spruce and spruce. In the same full-sib family, there are great differences among varieties. Selecting 20% varieties can increase the seed quantity by 10- 15% compared with the traditional seed orchard. Branch diameter, stem straightness and resistance to white pine elephant were also significantly improved. Of the 65,438+0,500-20 million saplings each year, about 250,000 trees from the southeast are produced (Greg Adams, 2065,438+05, Personal newsletter). At the age of 10, 233 clones from 27 families were used in the clone experiment, which was planted in three locations. When the best clone 10-30 is selected, the yield of seeds in the seed orchard is increased by about 48% (http://treebredex.eu/img/pdf/vegprop-0409-pres-park-ys.pdf).

We also contacted other conifer forestry companies, including Coillte Limited in Ireland, Weyerhaeuser in the United States and Hancock Queensland Plantation (HQP) in Australia. These companies have long-term and extensive interests in clonal forestry, and some of them have several series of cloning experiments (such as HQP), although the current situation is not available due to intellectual property issues or trade secrets.

The main problem limiting the application of clonal forestry in conifers is the cost of reproduction, especially the use of selenium. For example, in 2008, the branch cost of loblolly pine was 5-6 times that of similar seedlings, while the experience of spruce and pine shows that the difference may actually be close to 8-10 times (Lu Le Walter et al., 20 13). This technology in Sweden shows that the use cost of selenium is twice as high as that of seedlings (Ola Rosvall 20 15, personal communication). All these costs need to be balanced with advantages, including shortening the time for the improved materials to be put into commercial use.

Many broad-leaved tree species can remain young after a period of progeny determination, which makes the tested materials easy to propagate. This promoted the success of cloning forestry of this species. Taking eucalyptus as an example, the clonal afforestation of broad-leaved trees was successfully realized.

Eucalyptus in Brazil. Brazil has about 4.5 million hectares of eucalyptus plantations, and the planting area is still expanding. The superiority of Eucalyptus grandis× Eucalyptus grandis hybrid combination and the easy reproduction of excellent clones make Eucalyptus hybrid clone forestry a successful textbook example of breeding and reproduction. Recorded gene acquisition is hard to find. The problem is that in the commercial stands planted in the 1970s and 1980s, huge profits were made in the early stage only by selecting a large number of rare recombinants (Dario Gratapaglia, 20 13, personal newsletter). These seeds were collected in early species/provenance/offspring experiments, including the famous Rio Clara stand introduced in the early 20th century. Bison et al. (2006) reported that the performance of interspecific hybrids of Eucalyptus grandis was 38.7% higher than that of intraspecific hybrids. In the case of similar genetic gain obtained by clonal selection, the total genetic gain obtained by hybrid combining clonal selection may be considerable. The clones selected by Aracruz for the first time (they won the Wohlenberg Prize) gained more than 65,438+000% compared with the commercial stands at that time, and easily produced about 30-40 m3/ha/ year, while the average yield of extremely low-yield and variable stands was 65,438+00-65,438+05m3/ha. Unmodified seeds (Dario Guerra Thapaliya 20 13, personal newsletter). After this initial success, the income is increasing. At present, the average growth rate of industrial plantations is about 45 cubic meters/hectare/year, and the best place is as high as 65 cubic meters. Fibria is a large listed company, which produced about 5 million metric tons of eucalyptus pulp in 20 14. By introducing unified superior clones from 1980, the planting productivity increased from 6.4 metric tons per year in the 1970s to 10.6 metric tons in 2000. In 20 12 years, the pulp output will further increase to1.9 tons, and will reach 15 tons in 2025 (Wu 20 15).

In Brazil, most enterprises plant 10 to 14 clones every year for 5-8 years. Rezende et al. (20 13) reported that the average yield growth rate was 25% higher than that of commercial plantation seedlings. They also suggest replacing two to five new clones every three to four years, and changing the clone combination every 10- 15 years. With regard to diseases and abiotic threats, cloning is regarded as a solution, not a problem. New diseases such as rot, rust and drought have appeared, but cloning is considered as the fastest solution, mainly the genetic variation of eucalyptus resources, which can resist most diseases. Up to now, there is no disaster record specifically attributed to cloning technology.

Eucalyptus is in China. Eucalyptus planting in China is another successful case of hardwood clonal forestry. Eucalyptus plantation was only 300,000 hectares in 1970, and gradually increased to 400,000 hectares in 1980, and gradually increased to 700,000 hectares in the mid-1990s. Eucalyptus planting area in China has increased rapidly, which was about 6.5438+0.5 million hectares in 2005 and 3.7 million hectares in 2006. It is estimated that the planting area of Dongmen clones (mainly 17 clones) exceeds 2.6 million hectares, and it is estimated that about 80% of the planting area has 5 clones of DH32 families (Huang et al. 20 12). In Dongmen, the main commercial cloning experiment started at 199 1, which was selected from a cross family experiment of 1988. Among them, popular cross families DH32 (Eucalyptus urophylla U 16× Eucalyptus grandis G46) and DH33 (U/kloc-) were found. The special cloning experiment of 90 clones in 1992 shows that hybrid clones (especially those between broad-leaved trees and giant broad-leaved trees) are far superior to pure clones in growth, and also superior to local clones and giant broad-leaved trees × giant broad-leaved trees. Cloned from Aracruz, Brazil (Huang et al. 20 12).

With the use of new hybrid varieties, the productivity of eucalyptus plantations in China increased from less than 7 m3/ha/ year before the mid-1970s to an average of 65,438+00-65,438+02 m3/ha/year in the late 1980s. Since then, clonal forestry has appeared and improved afforestation methods have been improved. The average productivity is about 20m3/ha/year (Arnold, 2005). At the same time, the crop rotation period has been reduced from more than 65,438+00 years to 6-7 years, even shorter in some areas, with an annual return of 65,438+0,548 yuan (65,438+0,935 Swedish kronor) per hectare.

In Dongmen demonstration planting, the best clones of DH32 and DH33 families were harvested at 7 years old, with an average annual output of 35.438+0 m3/ha. It is reported that Dongguang Forest Farm near APP Pulp Factory in Hainan Island uses clone DH32-29 artificial forest, and the five-year MAI is 67 cubic meters/hectare/year on basalt soil. In the past 15 years, 7 of the most popular commercial clones of 17 came from DH32 family and 3 from DH33. Therefore, the genetic basis of most eucalyptus plantations in China is very narrow. Due to the sensitivity to bacterial wilt and canker, the prevalence of clones from DH33 family decreased, and clone DH20 1-2 was basically stopped due to insect pests. Therefore, it is an ideal choice for planting in the future to update clones more frequently and increase the number of different clones.

However, not all eucalyptus trees are suitable for clonal forestry. For some species with weak rooting ability or limited edge and environment, family forestry with asexual propagation or seedling propagation may be more economical and sustainable (Griffin 20 14).

In dairy cows, genome selection (GS) was initiated by using whole genome dense markers, but no related experiments were conducted (Meuwissen et al. 200 1). GS promoted the rapid selection of excellent genotypes and accelerated the breeding cycle. In recent years, if the training population is closely related to the selection population, GS has been successfully introduced into tree breeding (resende et al.2012; Lin et al; Bartholome et al. 20 16), its efficiency is similar to phenotypic selection. The advantage of using GS for clonal selection is that the selection of GS can be carried out in the early stage of seedlings or newly germinated seeds. This may eliminate the need for long-term clonal testing of conifers. Therefore, combining GS with somatic embryogenesis may promote the development of clonal forestry.

(1) Theoretically, conifers can obtain 5-20% additional genetic gain through cloning experiments and configuration, instead of the gain that can be obtained by family forestry calculated by using estimated genetic parameters. The difference of extra gain is mainly due to the size of the population, the number of clones of the tested families and the accuracy of offspring detection, which has nothing to do with uncertainty. If the propagation success rate is less than 100%, the theoretical gain may decrease.

(2) According to the experimental results, the genetic gain achieved by conifers in clonal forestry experiment is higher than that in family forestry experiment, but there is little information about the number of clones configured in commercial plantation and the genetic gain achieved by commercial clonal plantation.

(3) Taking eucalyptus clone forestry as an example, when a few clones selected centrally are commercialized, the genetic gain of broad-leaved tree varieties is 25-50%. New eucalyptus plantations usually use about 5- 14 clones.

(4) Three theoretical studies on the number of clones needed to prevent potential biological threats all show that increasing the number of genotypes above a certain number has little effect on reducing the risk of loss. In an infinite population, 5-30 clones seem to provide the same "security", and the best diversity level may be 18 clones, with at least 6 clones.

(5) In order to implement clonal forestry and family forestry of asexual reproduction in Norwegian spruce and other species, it is suggested to estimate additive and non-additive genetic variation from existing family/cloning experiments to confirm the benefit prediction of clonal forestry relative to families. Y forestry. In addition, it is suggested to take appropriate control measures to carry out stable production test.

(6) It is also suggested to estimate the relative propagation and planting costs of different propagation types (seedlings and root cutting versus selenium), and analyze the overall rotation cost/benefit of Norwegian spruce and other species by discounted cash flow.

(7) Population genome tools (cloning and family forestry and wild) should be used to investigate the potential long-term diversity loss at landscape and species level.

(8) The application of clonal forestry technology can improve or adjust the existing breeding and experimental schemes. Combining genome selection at seedling stage or germination stage with SE can greatly promote the development of clonal forestry in the future, especially on conifers.