AU2011244984A1 - Method for producing rooted cutting of plant of the genus Eucalyptus and method for raising mother tree of the plant of the genus Eucalyptus for cutting - Google Patents

Abstract

A production method of rooted cuttings of genus Eucalyptus by promoting rooting of cutting taken from 5 mother tree, the method comprising using cuttings, whose diameter are between 1.8 mm and 5.0 mm and flexural strength are between 0.2 N and 6.0 N.

Description

Australian Patents Act 1990 - Regulation 3.2 ORIGINAL COMPLETE SPECIFICATION STANDARD PATENT Invention Title Method for producing rooted cutting of plant of the genus Eucalyptus and method for raising mother tree of the plant of the genus Eucalyptus for cutting The following statement is a full description of this invention, including the best method of performing it known to me/us: P/00/011 5102 5 Technical Field [0001] This invention relates to a method for producing rooted [0 cutting of the plant of the genus Eucalyptus and a method for raising a mother tree of the plant of the genus Eucalyptus for cutting. Technical Background [0002] 15 Eucalyptus is a seed plant and comes under the dicotyledon of Archichlamydeae and schizopetalus flowers, and it is a plant of the genus Eucalyptus that is one genus of Myrtaceae (including about 90 genera such as genus of fruit tree "Feijoa") and is an evergreen broad-leaved tree 20 of Oceanian origin. Plants of the genus Eucalyptus are excellent in growing ability. In addition thereto, they have high specific gravity and high pulp yields and are industrially suitable for wood production and pulp materials, and they are planted in various parts of the 25 world. [0003] Of these, Eucalyptus globulus, Eucalyptus nitens, Eucalyptus grandis, Eucalyptus europhylla, Eucalyptus eurograndis, Eucalyptus citriodora and Eucalyptus 30 camaldulensis are species of trees that are planted worldwide in broadest areas in many cases, and they are employed in Chile and Australia even in the overseas afforestation projects of our paper manufacturing industries. 35 [0004] Plants of the genus Eucalyptus are the most important species of trees as pulp materials and wood resources, and planted in various counties in the world. Since, however, la the plants of the genus Eucalyptus are hard to multiply efficiently by cutting or tissue culture (see, for example, Non-Patent Document 1), it is actual practice to raise plantlets by seedling to plant trees. The seedling 5 involves a problem that since plantlets are not genetically uniform and become non-uniform in growth, the yield is low or is not predictable. [0005] As a method of overcoming these problems, a method of 0 producing excellent seedlings selected on the basis of certain standards using a cloning technology is thinkable. If an individual that exhibits excellent traits (growing ability and tree form) is propagated clonally and the plant can be grown adequately, the yield can be improved, and the [5 cost of manufacturing of paper can be decreased. The technology of effective clonal propagation, i.e., an improvement in the rooting percentage of cuttings is demanded worldwide since it has a major effect on the productivity of clonal plantlets. 20 (0006) The cloning technology includes a method in which cutting and tissue culture are applied (e.g., Patent Document 1). Since, however, the tissue culture method requires a plantlet cost and skilled culturing techniques, 25 it is difficult to practice the method in a production site where mass production is essential. [0007] The cutting is a vegetative propagation method in which the cut edges of cuttings are inserted in a propagation 30 media and allowed to root therein to make independent plant individuals. This method is in widespread use for herbs to woody plants as a simple method of producing a large amount of clonal plantlets having the same genetic traits as those of a mother tree. In reality, therefore, the clonal 35 propagation method is limited to cuttings, while the clonal propagation of a tree practically can include very many difficulties. [0008] 2 The rooting ability of the cutting has a large effect on the productivity of plantlets, and it is an essential object to improve the rooting ability. Various culturing methods for improving the rooting ability has been studied, 5 and there have been proposed many methods such as physical pretreatments for rooting, including the optimization of phytohormone (for example, see Patent Document 2), the use of a rooting promoter (for example, see Patent Document 3), the optimization of a carbon dioxide gas concentration or 0 lighting conditions (for example, see Patent Documents 4 and 5),pretreatment by a chemical for rooting (for example, see Patent Documents 6 and 7), and the wounding of base portion of a branch or stem or leave to allow it root or the peeling of an epidermis in the vicinity of cut section L5 of a base portion (for example, see Patent Document 8). [0009] According to the methods of Patent Documents 2 to 8, the rotting ratio of cuttings is greatly improved. However, the ability to root from a cutting has a great influence on 20 the rooting ability of the cutting itself. It is necessary to secure cuttings excellent in rooting ability as a material in order to improve the ability to root from cuttings. [0010] 25 As a method of efficiently producing cuttings by obtaining cuttings of plants of the genus Eucalyptus excellent in rooting ability, there has been proposed a method of using cuttings having a ratio of length (T) in the axial direction to a maximum diameter (R) (R/T) of 0.9 30 or more (for example, see Patent Document 9) . However, the rooting ability of cuttings of plants of the genus Eucalyptus is not determined by a dimensional factor alone, and the above study has a problem that the strength and juvenility of cuttings cannot be covered. 35 [00111 Meanwhile, those chemicals which are used for growth regulation of plants have effects of plant growth regulators such as the promotion of rooting and survival of 3 plants, better seedling, the prevention of scars by transplant, the promotion of lateral shoots, the prevention of axillary shoots, the promotion of flowering, fruit setting, enlargement, coloring and maturation period, 5 growth control (growth retardation), drop control, fruit thinning, the prevention of a scar skin, the prevention of harmful effect of medicines and the promotion of healing. The plant growth regulator used for the growth control (growth retardation) among these includes ancymidol, 0 dikegulac, daminozide, mefluidide, a Chlomequat solution, paclobutorazol granules, inabenfide granules, etc., and they contribute to the yields of crops and improvements in product qualities. The use thereof is limited to flowers, ornamental plants, garden trees and shrubs, lawn, wheat and L5 rice, and they have effective components dependent upon concentrations, so that the method of avoiding chemical injury and the selection of a use period require knowledge and experience. [0012) 20 For plants, roots not only absorb water and nutrient elements necessary for their growth, but also support their above-ground parts to prevent them from falling down, or perform a wide variety of functions, and it has been long since pointed out in the realm of agriculture to 25 sufficiently develop the roots of plants (for example, see Non-Patent Documents 2 and 3). [0013] However, there are few plant growth regulators that promote the development of roots, and their effects are not 30 sufficient, either. Further, they have undesirable activities in many cases. Those auxin-containing compounds which are now widely used as rooting compounds sometimes exert undesirable effects such as the epinastic bending of leaves, the twisting and breaking of stalks, the induction 35 of club root and, further, withering depending upon the species and states of plants and application concentrations. Therefore, the use method, use amount, etc., thereof are limited, and their activity to promote the development of 4 roots have not been fully satisfactory. [0014] Therefore, various methods of using growth regulators have been studied, and there are a method of efficiently 5 controlling the raising of plantlets on the basis of the growth retarding technology using a strain (for example, see Patent Document 10), the provision of a-ketol unsaturated fatty acid derivatives as plant growth regulators including the use as plant 0 flower-bud formation promoters or plant activators that exhibit performances of breaking of dormancy, rooting, the promotion of flowering, the promotion of flower setting and the promotion of elongation of grass stalks (for example, see Patent Document 11), the provision of lactone [5 derivatives and plant growth regulators and rooting inducers containing them as effective components (for example, see Patent Document 12), the provision of amide derivatives having high activity to promote the rooting of plants and having no substantial side effect and plant 20 growth regulators containing said amide derivatives as active components (for example, see Patent Document 13) and a method of producing a plant growth regulator obtained by mixing auxin, cytokinin, peptide and sildenafil citrate and a method of using the same (for example, see Patent 25 Document 14). [0015] Of these growth regulators, paclobutrazol that is one of plant growth regulators having sterilization activity has the activity of inhibiting the biological synthesis of 30 gibberellin in a plant and suppressing the cellular elongation that is the main action of gibberellin or the elongation of a plant height, so that it is used for the growth retardation of rice, fruit trees and horticultural crops and the decreasing of lodging. 35 [0016] As a method of improving the rooting ability of cuttings, the use of paclobutrazol that is an inhibitor through the gibberellins biosynthetic pathway has been also 5 studied for the production of rooted cuttings of plants of the genus Eucalyptus and the genus Acacia (for example, see Patent Document 15) . It is known that when cuttings are collected after a mother tree of peach or olive for 5 cuttings are treated with paclobutrazol followed by the plating of the collected cuttings after treatment with indole-3-butyric acid (IBA) that is a rooting promoter, the survival ratio and rooting percentage are improved (for example, see Non-Patent Documents 4 and 5). 0 [0017] None of Patent Document 15 and Non-Patent Documents 4 and 5 aim at improving the rooting percentage in relation to the effect duration of a plant growth regulator with considering growth characters depending upon trees. An L5 improvement in rooting percentage is observed when a plant growth regulator is added, while the point of the improvement in rooting percentage varies depending upon plant species, and even in the identical genus, the effect differs depending upon species. The problem is that no 20 optimum conditions for a maximum improvement in rooting percentage of the genus Eucalyptus can be found even if an improvement in rooting percentage is studied without focusing attention on the growth characters of a plant during a period from the application of a chemical to the 25 plant to the plating of cuttings. [Prior Art Documents] [Patent Documents] [0018] [Patent Document 1] JP 9-172892A 30 [Patent Document 2) JP 6-189646A [Patent Document 3] JP 6-199611A [Patent Document 4] JP 8-252038A [Patent Document 5] JP 2000-60332A [Patent Document 6] JP 11-243769A 35 [Patent Document 7] JP 2002-10710A [Patent Document 8] JP 11-69912A [Patent Document 9] JP 2006-6302A [Patent Document 10] JP 10-287520A 6 [Patent Document 11] JP 2006-151830A [Patent Document 12] JP 2006-151830A [Patent Document 13] JP 2001-139405A [Patent Document 14] JP 2001-58912A 5 [Patent Document 15] JP 2001-231355A [Non-Patent Documents] [0019] [Non-Patent Document 1] Kazuya Ito, "'Clonal Plantation of Eucalyptus globulus - Selection of Plus trees and Trial LO Plantation", Journal of Japan Technical Association of the Pulp and Paper Industry, Japan Technical Association of the Pulp and Paper Industry, 2006, Vol. 60, No. 4, p. 476-485 [Non-Patent Document 2] Compiled by Bootes et al, Physiology and Determination of Crop Yield, p. 65-93, 1994 15 [Non-Patent Document 3] Compiled by Nenojiten Hensyuu Iinkai (Editorial committee) of Neno Jiten (Cylopaedia of roots), p. 261-289, 1998 [Non-Patent Document 41 Wiesman, Z., Riov, J., Epistein, E., HortScience, 24(6), p. 908-909, 1989 20 [Non-Patent Document 5] Wiesman, Z., Lavee, S., Plant Growth Regulation 14, p. 83-90, 1994 Summary of the Invention Problems to be Solved by the Invention 25 [0020] The first object of this invention relates to a method for producing rooted cuttings of plants of the genus Eucalyptus, and it is to obtain those cuttings of plants of the genus Eucalyptus which are excellent in rooting ability, 30 and to improve the rooting percentage in cutting experiments to enable the efficient production of rooted cuttings and enable their excellent production. [0021] The second object of this invention relates to a method 35 of raising a mother tree of plant of the genus Eucalyptus for cuttings. Setting the timing for the growth regulating treatment of plants requires much labor since it is required to treat the plants many times while seeing how 7 they are growing, so that the growth regulation could not be carried out easily. Further, since cutting materials in a large quantity are required when the clonal propagation by cuttings is performed, the amount of materials that can 5 be collected is decreased if the growth retardation is carried out at an early stage of growing. That is, it is required to carry out growth retardation treatment of plants that have grown to a certain size. [0022] 0 The kind and concentration of a plant growth regulator differ depending upon purposes in treatment and species of plants, so that the plant growth regulator is required to be suitable for the plant and to have a concentration suitable for the plant. In a correlation between the 5 growth control and the rooting percentage of the material for propagation, the method of using a chemical differs in a thousand different ways among species of plants or if plants of the same genus are different in species. [0023] !0 It is an object of this invention to provide the technique of growing a mother tree with a growth regulator for clonal plantlet propagation of plants of the genus Eucalyptus that are employed in many cases as fast growing tree species of a pulp material. And, it is also an object ,5 of this invention to improve the rooting percentage of cuttings accordingly. Means to Solve the Problems [0024] 30 As a result of diligent studies for achieving the first object, attention has been focused on the diameter and flexural strength of cuttings and the cross-sectional area of a cutting and the ratio of xylem to the total cross sectional area, and the present studies have been completed 35 by having found that a cutting having these sizes in constant ranges has excellent rooting ability. [0025] (1) A method of producing rooted cuttings of plant of the 8 genus Eucalyptus by collecting cuttings from a mother tree and allowing the cuttings to root, characterized in that cuttings having a diameter of 1.8 to 5.0 mm and a flexural strength of 0.2 to 6.0 N are used. 5 (2) A method of producing rooted cuttings of plant of the genus Eucalyptus by collecting cuttings from a mother tree and allowing the cuttings to root, characterized in that cuttings having a cross-sectional area of 4.5 to 20.5 mm 2 10 and a xylem ratio of from 0.15 to 0.48 are used. (3) A method of producing rooted cuttings of plant of the genus Eucalyptus by collecting cuttings from a mother tree treated with a plant growth regulator and allowing the 15 cuttings to root, characterized in that cuttings having a diameter of 1.9 to 4.5 mm and a flexural strength of 0.4 to 5.4 N are used. (4) A method of producing rooted cuttings of plant of the 20 genus Eucalyptus by collecting cuttings from a mother tree treated with a plant growth regulator and allowing the cuttings to root, characterized in that cuttings having a cross-sectional area of 5.6 to 23.0 mm2 and a xylem ratio of from 0.10 to 0.45 are used. 25 (5) A method of producing rooted cuttings of plant of the genus Eucalyptus as recited in the above (3) or (4), wherein a growth regulator is applied to soil around the mother tree. 30 (6) A method of producing rooted cuttings of plant of the genus Eucalyptus as recited in any one of the above (1) to (5), wherein the mother tree from which the cuttings are taken is selected from a tree from a rooted cutting, a 35 grafted tree or a tree from a seedling. (7) A method of producing rooted cuttings of plant of the genus Eucalyptus as recited in any one of the above (1) to 9 (6), wherein the plant of the genus Eucalyptus is Eucalyptus globulus, Eucalyptus nitens, Eucalyptus grandis, Eucalyptus europhylla, Eucalyptus eurograndis, Eucalyptus citriodora or Eucalyptus camaldulensis. 5 [0026] As a result of diligent studies for achieving the above second object, diligent studies have been made while optimizing a time period from the growth retardation of 10 plants of the Eucalyptus to the collection of cuttings, and this invention has been completed by focusing attention on the amount of a chemical, the time period for raising mother trees after the retardation of growth thereof and the growing ability of mother trees and finding out an 15 optimum point at which the rooting percentage is the most improved in correlation to the elongation of the trees. [0027] (8) A method of raising a mother tree of plant of the genus Eucalyptus for cuttings, which comprises spraying a plant ,0 growth regulator containing paclobutrazol as an effective component to soil in an effective component amount of 1.25 mg or more per liter of the soil. (9) A method of raising a mother tree of plant of the genus ,5 Eucalyptus for cuttings as recited in the above (8), wherein a time period for raising the mother tree of plant of the genus Eucalyptus for cuttings from the spraying of the plant growth regulator to the soil to the collection of the cuttings is set for one month or less. 30 (10) A method of raising a mother tree of plant of the genus Eucalyptus for cuttings as recited in the above (8), wherein a time period for raising the mother tree of plant of the genus Eucalyptus for cuttings from the spraying of 35 the plant growth regulator to the soil to a raising operation is set for a time period for which the elongation of the mother tree is inhibited such that it is 20 cm or less. 10 (11) A method of raising a mother tree of plant of the genus Eucalyptus for cuttings as recited in any one of the above (8) to (10), wherein the mother tree for cuttings has a 5 height of 90 to 140 cm. (12) A method of raising a mother tree of plant of the genus Eucalyptus for cuttings as recited in any one of the above (8) to (11), wherein the plant of the genus Eucalyptus is 10 Eucalyptus globulus, Eucalyptus nitens, Eucalyptus grandis, Eucalyptus europhylla, Eucalyptus eurograndis, Eucalyptus citriodora or Eucalyptus camaldulensis. Effect of the Invention 15 [0028] The first effect of this invention is that cuttings of plants of the genus Eucalyptus excellent in rooting ability can be easily selected. Therefore, the ability of rooting from cuttings can be improved, and plantlets can be ?0 efficiently produced. [0029] The second effect of this invention is that the rooting ability can be optimized by determining the effective component (paclobutrazol) amount to the mother tree for !5 cuttings. Further, the rooting percentage can be further improved by determining the height of the mother tree for cuttings and the time period for raising the mother tree after the application of the chemical. 30 Brief Explanation of Drawings [0030] Fig. 1 is a graph showing a relationship among the diameter and flexural strength of cuttings and the rooting ability of the cuttings in this invention (1). 35 Fig. 2 is a photograph showing a state in which a cutting is measured for a flexural strength. Fig. 3 is a graph showing a relationship among the cross-sectional area and xylem ratio of cuttings and the 11 rooting ability of the cuttings in this invention (2). Fig. 4 is a graph showing a relationship among the diameter and flexural strength of cuttings and the rooting ability of the cuttings in Example of this invention (3). 5 Fig. 5 is a graph showing a relationship among the diameter and flexural strength of cuttings and the rooting ability of the cuttings in Referential Example of this invention (3). Fig. 6 is a graph showing a relationship among the 10 cross-sectional area and xylem ratio of cuttings and the rooting ability of the cuttings in Example of this invention (4). Fig. 7 is a graph showing a relationship among the cross-sectional area and xylem ratio of cuttings and the 15 rooting ability of the cuttings in Referential Example of this invention (4). Preferred Embodiments of the Invention [0031] 20 The plant of the genus Eucalyptus in this invention is selected from the group consisting of Eucalyptus globulus, Eucalyptus nitens, Eucalyptus grandis, Eucalyptus europhylla, Eucalyptus eurograndis, Eucalyptus citriodora or Eucalyptus camaldulensis. Of these, Eucalyptus globulus 25 and Eucalyptus grandis are more preferably used, and Eucalyptus globulus can be particularly preferably used. [0032] The first invention of this invention will be explained in detail below. First, embodiments of the plant of the 30 genus Eucalyptus that is used as a mother tree for cuttings will be explained. The mother tree for cutting includes a tree from a seedling, a grafted tree and a mother tree from a rooted cutting. It is preferably a one-year-old to two years-old mother tree. In general, cuttings having high 35 rooting ability are obtained from a healthy mother tree. A mother tree is preferably planted under adequate nutrient conditions under adequate environmental conditions. Preferably, a mother tree is irrigated to such an extent 12 that the plant is not wilted, and a fertilizer is applied about once a week. The fertilizer can be selected from commercially available liquid fertilizers. It is applied in a concentration of about 1-2 g/L. The temperature is 5 preferably maintained at 20 to 40*C. An environment in which the daily minimum temperature falls below 5*C continuously for several days is not preferred. [0033] The method of pre-treating a mother tree with a plant 10 growth regulator will be explained. The method includes a method of treating the soil around a mother tree with granules or a mixed fertilizer, and a method of treating the soil around a mother tree with a wettable powder. The time for the treatment is more preferably a time when 15 shoots of a plant start elongating growths before summer, while it is not specially limited so long as the plant is having the elongating growth. [0034] As kinds of the plant growth regulator, the inhibitor 20 through a gibberellin biosynthetic pathway is largely classified into triazole inhibitors (paclobutrazol and uniconazole), pyrimidine inhibitors (ancymidol and flurprimidol), isonicotinamide inhibitors (inabenfide), quaternary amine inhibitors (Chlomequat) and others ,5 (Daminozide and Prohexadione). The inhibitor is not specially limited so long as the elongation is inhibited. [0035] The amount of the plant growth regulator differs depending upon its kind and cannot be uniformly determined. 30 The amount is preferably determined according to the amount used for inhibiting the elongation, and it is more preferably an amount that maximizes the improvement in the rooting percentage of cuttings. For example, when paclobutrazol is used, the amount thereof is preferably 35 1.25 to 6.25 mg per liter of culture soil. [0036] In the mother tree of plant of the genus Eucalyptus that is treated with a plant growth regulator, the 13 elongating growth is inhibited in about 2 weeks after the treatment, and its growth is retarded. The tree treated by the growth retardant shows a change in form like the length of internodes and the size of leaves are smaller. The 5 cuttings that have undergone the above changes are suitable for producing rooted cuttings. It is therefore preferred to raise the mother tree for 2 weeks or more but one month or less after the spraying of the plant growth regulator to the soil. 10 [0037] The cuttings for rooted cuttings are selected from shoots that are young shoots up to current shoots or lateral shoots occurring therein and that can be materials. The collected shoots are immediately immersed in water that 15 has been prepared. More preferably, it is desirable to collect shoots during summer months for which plants vigorously have elongating growths. [0038] Collected shoots or lateral shoots are cut to one node 20 length in a state in which two leaves are on, and these one node long shoots are used as cuttings. In this case, the cuttings preferably have a one-node length of 3 cm or more. The diameter size of the shoots to be used as cuttings will be described in Examples to be described later. 25 [00391 A hormonal agent such as indole-3-butyric acid is applied to the base portion of each of the cuttings prepared, and each cutting is inserted into a sponge-like porous material full of water-holding ability and air 30 permeability (shaped culture soil obtained by adding culture soil composed mainly of peat moss to coconut palm fibers as a main component, adding a hydrophilic urethane prepolymer as a shaping material and shaping the mixture in the form of sponge) until it is kept 1.5 cm deep from the 35 lowest portion of the cutting, and rooted cuttings will be made. When the above propagation media is used, workability such as the planting of cuttings, the confirming of rooting and potting can be improved. 14 [0040] The propagation medium can be selected from general culture soils such as reddish soil, kanuma soil, peat moss, vermiculite, pearlite, etc., and these can be used singly 5 or as a proper mixture. These porous materials are very easily dryable, and this shapeable culture soil is filled in a tray having a height of 5.5 cm and a diameter of 4.5 cm, the tray being filled with soil having good water holding ability such as peat and having a water discharge 10 outlet, and they are used for making rooted cuttings. [0041] The rooted cuttings are irrigation-controlled once or twice a day so that they are not too dry, and they are left for 6 to 8 weeks. 15 [0042] In the first invention of this invention, studies were made of standards for selecting cuttings excellent in rooting ability, and as a result, standards are taken on the basis of a dimension (diameter) and flexural strength 20 or a dimension (cross-sectional area) and a xylem ratio, and it has been found that when these elements satisfy constant values of standards, there is a high possibility for cuttings to have high rooting ability. This invention has been accordingly completed. 25 [0043] The second invention of this invention will be explained. The use of the plant growth regulator of this invention is not mainly for the purpose of retarding the growth of plants as its effect, but is limited to the 30 clonal propagation of plant of the genus Eucalyptus as an object. And, optimum conditions for improvements in rooting percentage are searched for while obtaining a correlation between the endurance of the effect of inhibiting the height of plants from increasing and the 35 rooting capability, and attention is focused on improvements in productivity. [0044] The embodiment of the mother tree of the genus 15 Eucalyptus for cuttings may be any one of a potted tree and a tree from seedling grown in the open, and a tree in a natural form is more preferred than a tree obtained by pruning trees and raising sprouting shoots. The reason 5 therefor is as follows. When the treatment for growth retardation is carried out, it is required to measure tree heights and axillary shoots for elongations as indexes for the growth retardation effect, and when the latter axillary shoots are measured, the pruned mother trees come to be 10 measured in more places, and the measurement is complicated. [0045] As a mother tree for cuttings, not only a tree from a seedling but also a clonal tree rejuvenated by cutting, grafting or tissue culturing may be used. The tree age of 15 the mother tree for cutting is not specially limited, while a younger tree is preferred since cuttings from it have high rooting ability. [0046] The method of pre-treating the mother tree with a plant 10 growth regulator will be explained below. The method of treating it with a plant growth regulator includes a method of treating the soil around the mother tree with granules or a mixed fertilizer, and a method of treating the soil around the mother tree with a wettable powder. The time for !5 the treatment is preferably a time when young shoots start elongating growths before summer, while it is not specially limited so long as they have elongating growths. [0047] As kinds of the plant growth regulator, the inhibitor 30 through a gibberellin biosynthetic pathway is largely classified into triazole inhibitors (paclobutrazol and uniconazole), pyrimidine inhibitors (ancymidol and flurprimidol), isonicotinamide inhibitors (inabenfide), quaternary amine inhibitors (Chlomequat) and others 35 (Daminozide and Prohexadione). As a kind that is in particular used in many cases for promoting the rooting, paclobutrazol included in the triazole inhibitor is preferred, and is used in this invention. 16 [0048] The amount of the plant growth regulator differs depending upon its kind and cannot be uniformly determined. The amount is preferably determined according to the amount 5 used for inhibiting the elongation (growth retardation) based on the regulation of inter-node elongation that is an end of use of each chemical. Since, however, the effect thereof is in correlation with the height of a mother tree or growing ability, it is required to fully examine the 10 amount according to the growth traits of a plant to be intended. In this invention, the plant growth regulator containing paclobutrazol as an effective component is sprayed to the soil in an amount of 1.25 mg or more of the effective component per liter of the culture soil for the 15 mother tree. When the amount of the plant growth regulator containing paclobutrazol is less than 1.25 mg as an effective component, the plant is retarded in growth, but there is involved a problem that a plant having difficulties in rooting is not improved in rooting 20 percentage. The upper limit thereof is preferably 6.25 mg or less for a reason that the rooting is reliably improved within a range in which no chemical injury is caused. [0049] Plants of the genus Eucalyptus treated with the plant 25 growth regulator are inhibited from having elongating growths in about 2 weeks after the treatment to be retarded in growth. Plants retarded in growths show changes in form like the length of internodes and the size of leaves are smaller. Cuttings that have the above changes in form are 30 suitable for producing rooted cuttings. It is therefore preferred to raise the mother tree for 2 weeks or more after the plant growth regulator is sprayed to the soil. [0050] The time period for raising the mother tree from the 35 spraying of the plant growth regulator to the soil to the collecting of cuttings is preferably determined to be 1 month or less. When the above time period is set for 1 month or less, the advantage is that cuttings can be 17 collected by controlling the mother trees for a short period of time, and that shoots as cutting materials can be raised so sooner using similar mother trees after the cuttings are collected. 5 [0051] As another index, the time period for raising the mother tree from the spraying of the plant growth regulator to the soil to the collecting of cuttings is determined to be a period for which the elongation of the mother tree is 10 so inhibited that it is 20 cm or less. When the elongation of the mother tree exceeds 20 cm, there is sometimes caused a problem that the rooting percentage is decreased. Further, for a reason that a large amount of cuttings as materials cannot be secured when plants are too retarded in 15 growth, the elongation of the mother tree is preferably 10 cm or more. [0052] The height of the mother tree is preferably 90 to 140 cm, more preferably 95 cm to 130 cm, still more preferably 20 100 to 120 cm. When the height of the mother tree is less than 90 cm, the absolute number of cutting materials obtained from the mother tree is eventually small, and there is sometimes involved a problem that since shoots having a small node length are produced, the efficiency of 25 collecting cuttings is decreased. Further, when it exceeds 140 cm, there is sometimes involved a problem that there is produced no effect on the retardation of growth, and that not any improvement in rooting percentage can be confirmed, depending upon an amount added. 30 [0053] The method of raising cuttings collected from the mother tree of which the growth is regulated by inserting them in cutting culture soil will be explained below. The cuttings for rooted cuttings are young shoots up to current 35 shoots and lateral shoots occurring therefrom, and shoots that can become materials are selected and collected. The collected shoots are immediately immersed in water that has been prepared. Collected shoots or lateral shoots are cut 18 to one node length in a state in which two leaves are on, and these one node long shoots are used as cuttings. After they are immersed in fungicide, the base of each cutting is treated with a hormonal agent containing indole-3-butyric 5 acid (IBA), and the cuttings are inserted into propagation medium. [0054] As the propagation medium, not only commercially available artificial culture soil (Oasis (trade name), rock 10 wool, etc.) but also general culture soils such as reddish soil, kanuma soil, peat moss, vermiculite, pearlite, etc., can be used singly, or a proper mixture of these can be used. The rooted cuttings are irrigation-controlled once or twice a day so that they are not too dry, and they are left 15 for 6 to 8 weeks. Examples [0055] Example 1 20 Rooted cuttings of Eucalyptus globulus were raised until their above-ground portions had a height of 100 cm or more, and these were used as mother trees to be used for the following experiments. In this case, pots had a volume of 24 liters each, and as a culture soil, a mixture of !5 black soil and culture soil in an amount ratio of 1:1 was used. [0056] Three mother trees obtained in the above manner were used to take 8 to 10 lateral shoots each, and they were cut 30 to each node. Internode including apex (about 1 mm) of axillary shoots was defined as "node 1". Since nodes 1 to 3 were very short in length and soft in stiffness, cuttings were not prepared from these internodes. [0057] 35 The remaining shoots were cut and separated into fifth to 15th nodes, and cuttings of each node were planted. An IBA/talc powder in an amount of 8,000 ppm was applied to the base of each cutting, the cuttings were inserted in 19 shaped culture soils, and the shaped culture soils were placed in a tray filled with peat/ vermiculite = 1:1 (v/v) to have rooted cuttings. They were left in a greenhouse having a temperature of 26*C and a relative humidity of 5 80 %, and after 6 weeks, each node was examined for a rooting percentage. [0058] Before the cuttings were planted, the cutting of each node of the mother trees was measured for a diameter with a 10 vernier caliper. Further, each cutting was measured for a flexural strength. The evaluation of the above flexural strength is an effective means since a load required for a constant displacement is examined nondestructively. For the method of selecting cuttings in this Example, the 15 following apparatus and measurement method are preferred. A flexural strength was measured with a universal tester such as a bench material tester (trade name: STA-1150, supplied by Orientec Co., Ltd.) by applying a load in the compression direction at a measurement speed of 0.5 20 mm/minute at a displacement of 0.5 mm. Fig. 2 is a photograph showing a state in which the flexural strength is measured. [0059] In this test, the distance set between supporting !5 points was 2.5 cm. When the distance set between the supporting points was larger than this value, some samples were immeasurable since they had insufficient lengths. Since samples measured here are then used for the cuttings planting test, the measurement is required to be carried 30 out nondestructively. It is generally said that in a stress-strain curve of a material such as steel, the material is destroyed when a stress of elastic limit or more is applied. When a plant material is measured, no general specification is available, so that, as a value at 35 which the sample was not destroyed, a time at which a stress value that was a half or less of a load applied to the elastic limit was reached was set at an end of the measurement. And displacement was set to 0.5 mm. 20 [0060] When the measurement speed exceeds 0.5 mm/minute, the displacement of a sample fails to catch up with the exertion of a load, and the data obtained varies, so that 5 the measurement speed is set at 0.5 mm/minute. [0061] Concerning the direction of the sample, the cross section of each cutting had a nearly square form, and the sample was placed such that its long side lied. That is 10 because the flexural strength differs depending upon when the long side was up or lied. The sample was placed such that the load was applied to the center of each cutting. [0062] Fig. 1 shows rooting percentages 6 weeks after the 15 cuttings were planted. In Fig. 1, the lower Figure is an enlarged view of the upper Figure, in which the range of flexural strength was 0 to 2.ON. In Figures, one point corresponds to one cutting, "o" shows a rooted cutting, and "x" shows a cutting that did not root. 20 [0063] As is clear in Fig. 1, cuttings of which the many rootings were observed had a diameter of 1.8 to 5.0 mm and a flexural strength of 0.2 to 6.0 N. Cuttings having a diameter of 2.6 to 3.9 mm and a flexural strength of 0.5 to ,5 4.0 N are more preferred, and cuttings having a diameter of 2.6 to 3.6 mm and a flexural strength of 1.0 to 2.0 N are still more preferred. On the other hand, cuttings having a diameter of over 5.0 mm, cuttings having a diameter of less than 1.8 mm and cuttings having a diameter of 1.8 to 5.0 mm 30 but a flexural strength of over 6.0 N exhibited a sharp decrease in rooting ability. [00641 Example 2 35 Rooted cuttings of Eucalyptus globulus were raised until their above-ground portions had a height of 100 cm or more, and these were used as mother trees to be used for the following experiments. In this case, pots had a volume 21 of 24 liters each, and as a culture soil, a mixture of black soil and culture soil in an amount ratio of 1:1 was used. [0065] 5 Three mother trees obtained in the above manner were used to take 8 to 10 lateral shoots each, and they were cut to each node. Internode including apex (about 1 mm) of axillary shoots was defined as "node 1". Since nodes 1 to 3 were very short in length and soft in stiffness, cuttings 10 were not prepared from these internodes. [0066] The remaining shoots were cut and separated into fifth to 15th nodes, and cuttings of each node were planted. An IBA/talc powder in an amount of 8,000 ppm was applied to 15 the base of each cutting, the cuttings were inserted in shaped culture soils, and the shaped culture soils were placed in a tray filled with peat/ vermiculite = 1:1 (v/v) to have rooted cuttings. They were left in a greenhouse having a temperature of 26*C and a relative humidity of 20 80 %, and after 6 weeks, each node was examined for a rooting percentage. [0067] The tissue of stem of each cutting was stored in a solution containing 50 % ethanol, acetic acid and formalin 25 = 18:1:1 (v/v/v). Cross-sectional tissues of these cuttings were cut to a thickness of 50 pm with an electric refrigeration type freezing microtome (supplied by Komatsu Electronics Inc.). Then, lignified portions were stained with a phloroglucin hydrochloric acid staining method. 30 Each cut sample was observed through an optical microscope DMLB30FL (Leica), and the cross-sectional areas and the areas of xylem and piths were calculated using MICROSCOPE VHX-900 (supplied by Keyence Corporation). Then, the ratio of xylem area to total cross sectional area at the basal 35 part of cuttings was calculated. Fig. 3 is a graph showing the results as the cross-sectional areas and the xylem ratios. In the graph, one point corresponds to one cutting, "o" indicates a rooted cutting, and "x" indicates a cutting 22 that did not root. [0068] As is clear in Fig. 3, optimum portions having high rooting ability can be narrowed down by examining the 5 correlation between the xylem ratio and the rooting percentage. Cuttings having high rooting percentages had a cross-sectional area in the range of 4.5 to 20.5 mm 2 and had a xylem ratio of from 0.15 to 0.48. Cuttings having a cross-sectional area of 8.0 to 12.0 mm 2 and a xylem ratio 10 of from 0.19 to 0.35 are more preferred. [0069] Cuttings of which the rooting was not easily observable had a cross-sectional area of over 20.5 mm 2 or had a cross sectional area of less than 4.5 mm 2 . In cuttings having a 15 cross-sectional area of over 20.5 mm2 , no sufficient water was secured from the base portion of each cutting, and it was found that they withered. In cuttings having a cross sectional area of less than 4.5 mm 2 , they were poor in rooting ability presumably because the amount of a 20 substance necessary for rooting was small, and it was simultaneously found that the survival ratio of the cuttings was decreased due to fungi. Further, when cuttings had an optimum cross-sectional area but had a xylem ratio of over 0.48, the possibility of no rooting was 25 very high. [0070] Example 3 Rooted cuttings of Eucalyptus globulus were raised until their above-ground portions had a height of 100 cm or 30 more, and 25 g of granules of a triazole-containing plant growth regulator SUMAREKUTO (trade name, an effective component content: 0.6 % of paclobutrazol, supplied by Ishihara Sangyo Kaisha, Ltd.) was sprayed to soil around each rooted cutting, and they were raised for 1 month (6.25 35 mg per liter of the culture soil). These were used as mother trees for the following experiments. In this case, each pot had a volume of 24 liters, and the culture soil prepared by mixing black soil and culture soil in a ratio 23 of 1:1 was used. [0071] Three mother trees obtained in the above manner were used to take 8 to 10 lateral shoots each, and they were cut 5 to each node. Internode including apex (about 1 mm) of axillary shoots was defined as "node 1". Since nodes 1 to 3 were very short in length and soft in stiffness, cuttings were not prepared from these internodes. [0072] 10 The remaining shoots were cut and separated into sixth to 15th nodes, and cuttings of each node were planted. An indole-3-butyric acid (IBA)/talc powder in an amount of 8,000 ppm was applied to the base of each cutting, the cuttings were inserted in shaped culture soils, and the 15 shaped culture soils were placed in a tray filled with peat/ vermiculite = 1:1 (v/v) to have rooted cuttings. They were left in a greenhouse having a temperature of 26 0 C and a relative humidity of 80 %, and after 6 weeks, each node was examined for a rooting percentage. 20 [0073] Before the cuttings were planted, the cutting of each node of the mother trees was measured for a diameter with a vernier caliper. Further, each cutting was also measured for a flexural strength. Fig. 4 shows rooting percentages 25 6 weeks after the cuttings were planted. In Fig. 4, the lower Figure is an enlarged view of the upper Figure, in which the flexural strength was 0 to 2.0 N. In the graph, one point corresponds to one cutting, "o" shows a rooted cutting, and "x" shows a cutting that did not root. 30 [0078] As is clear in Fig. 4, the cuttings of which many rootings were observed had a diameter of 1.9 to 4.5 mm and a flexural strength of 0.4 to 5.4 N. Cuttings having a diameter of 2.7 to 4.5 mm and a flexural strength of 0.5 to 35 4.0 N are more preferred. On the other hand, in cuttings having a diameter of over 4.5 mm, the rooting ability was sharply decreased. In cuttings obtained from mother trees that were retarded in growth with a plant growth regulator, 24 cuttings having a diameter of less than 1.9 mm had small node lengths and were soft and too immature as cuttings, and they were hence hard to plant and unsuitable. When such cuttings were planted, it was found that the survival 5 ratio of the cuttings was decreased due to fungi, etc. [0079] Referential Example 1 In Example 3, cuttings were collected from mother trees raised without the treatment with the plant growth 10 regulator in place of the mother trees treated with the plant growth regulator, and the cuttings were planted. Rooting percentages of the cuttings after 6 weeks were shown in Fig. 5. Rooting percentages of cuttings having a diameter of 1.9 to 4.5 mm and a flexural strength of 0.5 to 15 5.4 N in Example 3 and Referential Example 1 were calculated from data shown in Figs. 4 and 5, and Table 1 shows the rooting percentages. [0080] Table 1 Referential Example. 1 Example 3 Rotting percentage 62 80 (%) 20 [0081] As shown in Table 1, the cuttings that had a diameter of 1.9 to 4.5 mm and a flexural strength of 0.4 to 5.4 N and that were collected from the mother trees treated with 25 the plant growth regulator exhibited high rooting percentages as compared with the cuttings that had a diameter and a flexural strength in the same ranges and that were collected from the mother trees that were not treated with the plant growth regulator. 30 [0082] Example 4 Rooted cuttings of Eucalyptus globulus were raised until their above-ground portions had a height of 100 cm or more, and 25 g of granules of a triazole-containing plant 35 growth regulator SUMAREKUTO (trade name, an effective 25 component content, 0.6 % of paclobutrazol, supplied by Ishihara Sangyo Kaisha, Ltd.) were sprayed to soil around each rooted cutting, and they were raised for 1 month (6.25 mg per liter of the culture soil). These were used as 5 mother trees for the following experiments. In this case, each pot had a volume of 24 liters, and the culture soil prepared by mixing black soil and culture soil in a ratio of 1:1 was used. [00831 10 Three mother trees obtained in the above manner were used to take 8 to 10 lateral shoots each, and they were cut to each node. Internode including apex (about 1 mm) of axillary shoots was defined as "node 1". Since nodes 1 to 3 were very short in length and soft in stiffness, cuttings 15 were not prepared from these internodes. [0084] The remaining shoots were cut and separated into sixth to 13th nodes, and cuttings of each node were planted. An IBA/talc powder in an amount of 8,000 ppm was applied to 20 the base of each cutting, the cuttings were inserted in shaped culture soils, and the shaped culture soils were placed in a tray filled with peat/ vermiculite = 1:1 (v/v) to have rooted cuttings. They were left in a greenhouse having a temperature of 26 0 C and a relative humidity of 5 80 %, and after 6 weeks, each node was examined for a rooting percentage. [0085] The tissue of stem of each cutting was stored in a solution containing 50 % ethanol, acetic acid and formalin 30 = 18:1:1 (v/v/v). Cross-sectional tissues of these cuttings were cut to a thickness of 50 pm with an electric refrigeration type freezing microtome (supplied by Komatsu Electronics Inc.). Then, lignified portions were stained with a phloroglucin hydrochloric acid staining method. 35 Each cut sample was observed through an optical microscope DMLB30FL (Leica), and the cross-sectional areas and the areas of xylem and piths were calculated using MICROSCOPE VHX-900 (supplied by Keyence Corporation). Then, the ratio 26 of xylem area to total cross sectional area at the basal part of cuttings was calculated. Fig. 6 is a graph showing the results as the cross-sectional areas and the xylem ratios. In the graph, one point corresponds to one cutting, 5 "0" indicates a rooted cutting, and "x" indicates a cutting that did not root. [0086] As is clear in Fig. 6, optimum portions having high rooting ability can be narrowed down by examining the 10 correlation between the xylem ratio and the rooting percentage. Cuttings having high rooting percentages had a cross-sectional area in the range of 5.6 to 23.0 mm2 and had a xylem ratio of from 0.10 to 0.45. Cuttings having a cross-sectional area of 8.2 to 18.7 mm2 and a xylem ratio 15 of from 0.21 to 0.41 are more preferred. [0087) Cuttings of which the rooting was not easily observable had a cross-sectional area of over 23.0 mm or had a cross sectional area of less than 5.6 mm 2 . In cuttings having a 2 20 cross-sectional area of over 23.0 mm , no sufficient water was secured from the base portion of each cutting, and it was found that they withered. In cuttings obtained from the mother trees that were retarded in growth with a plant growth regulator, cuttings having a cross-sectional area of 25 less than 5.6 mm 2 had small node lengths and were soft and too immature as cutting materials, and they were hence hard to plant and unsuitable. When such cuttings were planted, it was found that the survival ratio of the cuttings was decreased due to fungi, etc. Further, even if the cross 30 sectional area was an optimum value, when the xylem ratio exceeded 0.45, the probability of no rooting was very high. [0088] In Example 4, cuttings were collected from mother trees raised without the treatment with the plant growth 35 regulator in place of the mother trees treated with the plant growth regulator, and the cuttings were planted. Fig. 7 shows their rooting percentages after 6 weeks. Rooting percentages of cuttings having a cross-sectional area in 27 the range of 5.6 to 23.0 mm 2 and a xylem ratio of from 0.10 to 0.45 in Example 4 and Referential Example 2 were calculated from data shown in Figs. 6 and 7, and Table 2 shows the rooting percentages. 5 [0089] Table 2 Referential Example 4 Example 2 Rooting percentage (%) [0090] As shown in Table 2, the cuttings that had a cross 10 sectional area in the range of 5.6 to 23.0 mm 2 and a xylem ratio of from 0.10 to 0.45 and a xylem ratio in the range of from 0.10 to 0.45 and that were collected from the mother trees treated with the plant growth regulator exhibited high rooting percentages as compared with the 15 cuttings that had a diameter and a flexural strength in the same ranges and that were collected from the mother trees that were not treated with the plant growth regulator. [0091] Example 5 20 Of clonal mother trees of Eucalyptus globulus, mother trees clone A having a tree height of 100 cm to 110 cm, mother trees clone B having a tree height of 100 to 120 cm and mother trees clone C having a tree height of 100 to 120 cm were used, and granules of a triazole-containing plant 25 growth regulator SUMAREKUTO (trade name, an effective component content, 0.6 % of paclobutrazol, supplied by Ishihara Sangyo Kaisha, Ltd.) were sprayed to a culture soil surface (around each rooted cutting) such that their amount of the effective component per liter of the soil was 30 1.25 mg or 6.25 mg each. In 4 weeks after the spraying of the plant growth regulator to the soil, cuttings were prepared, or about 3 cm long cuttings having two leaves each were collected. The base of each cutting was cut back with a knife and immersed in a fungicide solution for 5 35 seconds, and an indole-3-butric acid (IBA)/talc powder in 28 an amount of 8,000 ppm was applied to the base of each cutting. The cuttings were inserted in shaped culture soils, and the shaped culture soils were placed in a tray filled with peat/ vermiculite = 1:1 (v/v) to have rooted 5 cuttings. Three ramets were used per experimental plot. They were left in a greenhouse having a temperature of 26 0 C and a relative humidity of 80 %, and after 6 weeks, each cutting was examined for a rooting percentage. Table 3 shows the results of the elongation of the tree 10 height and the rooting percentages 4 weeks after the spraying to the soil. [0092] Table 3 Effective ' Rooting Clones amount(mg/ Elongation of tree percentage L) height (cm) 0 32.0±3.3 50.7 Outside the invention A 1.25 17.2±4.0 77.3 Within the invention Within the 6.25 16.7±2.5 81.3 invention 0 41.7±9.4 74.7 Outside the invention B 1.25 17.7±1.5 85.3 Within the invention 6.25 14.0±2.0 84.0 Within the invention 0 37.3±4.6 18.7 Outside the invention C 1.25 13.3±4.9 50.7 Within the invention 6.25 19.0±4.8 45.3 Within the .25 19.0±4.8 __ 45.3invention 15 [0093] As is shown in Table 3, the elongation of the tree height of the mother trees in the soils treated by spraying 1.25 mg/liter of soil or more of the effective component for 20 growth retardation was inhibited such that it was about 10 to 20 cm as compared with an elongation of about 30 to 50 cm of the elongation of mother trees in soils that were not 29 treated. Simultaneously, the cuttings obtained from the mother trees that were treated for growth retardation exhibited high rooting percentages. [0094] 5 It has been found that the mother trees are fully retarded in growth by spraying a growth-retarding effective component of 1.25 mg or more per liter of soil when the mother trees to which the plant growth regulator is to be applied have a height of 100 to 120 cm and raising the 10 mother trees for less than 1 month after the spraying or within a period for which the elongation of the mother trees does not exceed 20 cm, and that cuttings collected from the mother trees under the circumstances provided by replicating the above circumstances have the highest 15 rooting percentages. [0095] Example 6 Of clonal potted mother trees of Eucalyptus globulus propagated by cutting, clonal mother trees A having a tree 20 height of 90 cm to 140 cm were used, and granules of a triazole-containing plant growth regulator SUMAREKUTO (trade name, an effective component content, 0.6 % of paclobutrazol, supplied by Ishihara Sangyo Kaisha, Ltd.) were sprayed to a culture soil surface each such that their 25 amount of the effective component per liter of soil was 6.25 mg. In 2 weeks, 4 weeks, 8 weeks and 12 weeks after the treatment, cuttings were collected, and about 3 cm long cuttings having 2 leaves were prepared. The base of each cutting was cut back with a knife and immersed in a 30 fungicide solution for 5 seconds, and an indole-3-butric acid (IBA)/talc powder in an amount of 8,000 ppm was applied to the base of each cutting. The cuttings were inserted in shaped culture soils, and the shaped culture soils were placed in a tray filled with peat/ vermiculite = 35 1:1 (v/v) to have rooted cuttings. Three ramets were used per experimental plot. They were left in a greenhouse having a temperature of 26 0 C and a relative humidity of 80 %, and after 6 weeks, each cutting was examined for a 30 rooting percentage. Table 4 shows the results of the elongation of the tree height and the rooting percentages in each treatment period after the spraying to the soil. 5 [0096] Table 4 Raising period Treatment Elongation Rooting (week) after of tree percentage spraying of height (%) growth-retarder 2 No treatment 10.8 ±3.0 50.7 Growth-retarding 8.5 ±1.5 57.3 treatment 4 No treatment 32.0 ±3.3 50.7 Growth-retarding 16.7 ±2.5 81.3 treatment 8 No treatment 48.0 ±3.6 49.3 Growth-retarding 26.5 ±0.9 52.0 treatment 12 No treatment 76.0 ±2.6 30.6 Growth-retarding 33.2 ±13.5 22.7 treatment [0097] 10 As shown in Table 4, in the treatment plot of raising period of 2 weeks, the elongation of the tree height was inhibited to some extent as compared with the plot of no treatment, and the rooting percentage was also improved to some extent. In the plots of raising periods of 8 weeks and 15 12 weeks, the elongation of the tree height was about 25 cm or more, and it was not found that the cuttings from these mother trees had improved looting percentages as compared with those in the plots of no treatment. In the plot of raising period of 4 weeks, the elongation of the tree 20 height was about 14 cm to 19 cm or inhibited such that it was 20 cm or less, and it was found that the rooting percentage was remarkably improved. [0098] Example 7 25 Of clonal potted mother trees of Eucalyptus globulus 31 propagated by cutting, clonal mother trees D having a tree height of 90 cm to 110 cm were used, and granules of a triazole-containing plant growth regulator SUMAREKUTO (trade name, an effective component content, 0.6 % of 5 paclobutrazol, supplied by Ishihara Sangyo Kaisha, Ltd.) were sprayed to a potted culture soil surface in an amount of 1, 2, 3 or 5 g. Their amount of the effective component per liter of soil was 0.25 mg, 0.50 mg, 0.75 mg or 1.25 mg. [0099] 10 In one month after the treatment, about 3 cm long cuttings having 2 leaves were prepared. The base of each cutting was cut back with a knife and immersed in a fungicide solution for 5 seconds, and an indole-3-butric acid (IBA)/talc powder in an amount of 8,000 ppm was 15 applied to the base of each cutting. The cuttings were inserted in shaped culture soils, and the shaped culture soils were placed in a tray filled with peat/ vermiculite = 1:1 (v/v) to have rooted cuttings. Three ramets were used per experimental plot. They were left in a greenhouse 20 having a temperature of 26*C and a relative humidity of 80 %, and after 6 weeks, each cutting was examined for a rooting percentage. Table 5 shows the results of the elongation of the tree height one month after the treatment and the rooting percentages. 25 32 [0100] Table 5 Amount of granules 0 1 2 3 5 (g) Amount of effective component (mg/ 0 0.25 0.50 0.75 1.25 L) Elongation of tree height 39.2±2.9 17.3±2.8 39.2±2.1 35.0±3.1 15.7±2.4 (cm) Rooting p R ntg 62.7 56.0 40.0 44.0 69.3 percentage (%) Outside Outside Outside Outside Within the the the the the . invention invention invention invention [0101] 5 As shown in Table 5, in the treatment plot where the amount of effective component per liter of soil was 0.25 mg, the elongation of the tree height was inhibited to some extent as compared with the plot of no treatment, but no improvement in rooting percentage was found. In the 10 treatment plot of 0.50 mg and the treatment plot of 0.75 mg, no growth retardation effect was found, nor was found any improvement in rooting percentages. In contrast, in the treatment plot of 1.25 mg, the elongation of the mother trees was inhibited such that it was 20 cm or less, or the 15 growth retardation effect was found, and an improvement in rooting percentage was found. That is, it has been found that when the optimum amount of 1.25 mg of effective component of paclobutrazol per liter of soil is used to a certain height of the mother tree for cuttings, a 20 sufficient growth retardation effect can be produced, and that the rooting percentage is improved. Industrial Utility [0102] 25 The standard for selecting cuttings according to the first invention of this invention is one standard and can be utilized for mass-producing rooted cuttings of the genus Eucalyptus such as Eucalyptus globulus. 33 [0103] The second invention of this invention relates to a method of propagation of plants of the genus Eucalyptus, and they can be highly efficiently propagated and allowed 5 to be rooted cuttings. Throughout this specification and the claims which follow, unless the context requires otherwise, the word "comprise", and variations such as "comprises" and "comprising", will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integers or steps. The reference in this specification to any prior publication (or information derived from it), or to any matter which is known, is not, and should not be taken as an acknowledgment or admission or any form of suggestion that that prior publication (or information derived from it) or known matter forms part of the common general knowledge in the field of endeavour to which this specification relates. 34

Claims (12)

1. A method of producing rooted cuttings of plant of the genus Eucalyptus by collecting cuttings from a mother tree 5 and allowing the cuttings to root, characterized in that cuttings having a diameter of 1.8 to 5.0 mm and a flexural strength of 0.2 to 6.0 N are used.

2. A method of producing rooted cuttings of plant of the 10 genus Eucalyptus by collecting cuttings from a mother tree and allowing the cuttings to root, characterized in that cuttings having a cross-sectional area of 4.5 to 20.5 mm 2 and a xylem ratio of from 0.15 to 0.48 are used. 15

3. A method of producing rooted cuttings of plant of the genus Eucalyptus by collecting cuttings from a mother tree treated with a plant growth regulator and allowing the cuttings to root, characterized in that cuttings having a diameter of 1.9 to 4.5 mm and a flexural strength of 0.4 to 20 5.4 N are used.

4. A method of producing rooted cuttings of plant of the genus Eucalyptus by collecting cuttings from a mother tree treated with a plant growth regulator and allowing the 25 cuttings to root, characterized in that cuttings having a cross-sectional area of 5.6 to 23.0 mm 2 and a xylem ratio of from 0.10 to 0.45 are used.

5. The method of producing rooted cuttings of plant of the 30 genus Eucalyptus as recited in claim 3 or 4, wherein a growth regulator is applied to soil around the mother tree.

6. The method of producing rooted cuttings of plant of the genus Eucalyptus as recited in any one of claims 1 to 5, 35 wherein the mother tree from which the cuttings are taken is selected from a tree from a rooted cutting, a grafted tree or a tree from a seedling. 35

7. The method of producing rooted cuttings of plant of the genus Eucalyptus as recited in any one of claims 1 to 6, wherein the plant of the genus Eucalyptus is Eucalyptus globulus, Eucalyptus nitens, Eucalyptus grandis, Eucalyptus 5 europhylla, Eucalyptus eurograndis, Eucalyptus citriodora or Eucalyptus camaldulensis.

8. A method of raising a mother tree of plant of the genus Eucalyptus for cuttings, which comprises spraying a plant 10 growth regulator containing paclobutrazol as an effective component to soil in an effective component amount of 1.25 mg or more per liter of the soil.

9. The method of raising a mother tree of plant of the 15 genus Eucalyptus for cuttings as recited in claim 8, wherein a time period for raising the mother tree of plant of the genus Eucalyptus for cuttings from the spraying of the plant growth regulator to the soil to the collection of cuttings is set for one month or less. 20

10. The method of raising a mother tree of plant of the genus Eucalyptus for cuttings as recited in claim 8, wherein a time period for raising the mother tree of plant of the genus Eucalyptus for cuttings from the spraying of 25 the plant growth regulator to the soil to the collection of the cuttings is set for a time period for which the elongation of the mother tree is inhibited such that it is 20 cm or less. 30

11. The method of raising a mother tree of plant of the genus Eucalyptus for cuttings as recited in any one of claims 8 to 10, wherein the height of the mother tree is between 90 cm and 140 cm. 35

12. The method of raising a mother tree of plant of the genus Eucalyptus for cuttings as recited in any one of claims 8 to 11, wherein the plant of the genus Eucalyptus is Eucalyptus globulus, Eucalyptus nitens, Eucalyptus 36 grandis, Eucalyptus europhylla, Eucalyptus eurograndis, Eucalyptus citriodora or Eucalyptus camaldulensis. 37