Abstract:
A new flower-thinning agent is now provided, which is comprising cholesterol as the active component and advantageously exerts the flower-thinning effects superior to the known flower-thinning agents.

Description:
SUMMARY OF THE INVENTION 
     This invention relates to a new flower-thinning agent for use in the thinning treatment of flowers of fruit trees of various kinds. More particularly, this invention relates to a new flower-thinning agent which is applied to the flowers of cultivated fruit trees, for the purpose of partially removing or thinning the such flowers which are not required to undergo the fructification, while retaining on the tree such flowers which are required to fructify. 
     BACKGROUND OF THE INVENTION 
     In the cultivation of fruit trees of various kinds, it is essential to carry out preliminary work of picking off some of the flowers or fruit which are not required to fructify. This work of picking off the unrequired bodies of flowers or fruit is known as &#34;thinning&#34; of the flowers or fruit. Meanwhile, this thinning of the flowers or fruit usually requires a large amount of labor by workers. The thinning work must be done usually in the busy seasons of agriculture, and hence it is frequently difficult to carry out the thinning work at an appropriate time, so that the quality of the fruits cultivated and harvested is therefore sometimes lowered. 
     Heretofore, the methods for thinning the flower or fruit of fruit trees by chemical compounds have been extensively researched for almost all kinds of fruit trees such as apple tree, peach tree and others, and there has been proposed and developed a number of chemical thinning agents. The known chemical thinning agents may be classified according to their biological mechanisms of the action of these agents, and they may generally be classified into two groups, that is, a first group of such agents which act as a plant hormone and the second group of such agents which can exert phytotoxicity against the bodies or different organs of the flowers of fruit trees. While, such chemical thinning agents which have been extensively applied in practice for partial removal of the unrequired flowers or fruits are limited only to the formulation known under the name &#34;Ethyclozate&#34; for use in the thinning treatment of tangerine tree; the formulation known under the name &#34;Sevin&#34; for use in the thinning treatment of apple tree; and certain sulfur preparations for use in the thinning treatment of apple tree. The active components of the thinning agents known under the names &#34;Ethyclozate&#34; and &#34;Sevin&#34; belong to a class of plant hormone in nature, so that their flower-thinning effects can vary unfavorably depending on the biological conditions, of the trees treated and also on the weathering conditions, which is specifically observed with the plant hormone agents in general. On the other hand, the sulfur preparations practically employed as the chemical thinning agent are active in inhibiting the fertilization of flowers owing to its phytotoxicity to the stigma of the flower body, so that its flower-thinning activity is normally lower than those of the flower-thinning agents of plant hormone type. When the sulfur preparations are applied in an increased rate of application in an attempt to enhance its flower-thinning effects, the leaves and other portions of the fruit trees treated can often be damaged by the phytotoxicity of the sulfur preparations 
     For these reasons, there exists a great demand for a new flower-thinning chemical agent which is free from the above-mentioned drawbacks of the known chemical flower-thinning agents. In an attempt to meet this demand, we previously investigated a number of chemical compounds which were different in nature from the active components of the known thinning agents, and we already found that 2-pyrrolidone-5-carboxylic acid and salts thereof such as the sodium salt; and salts of an N-acylaminodicarboxylic acid; as well as esters of sucrose with a higher fatty acid and plant sterols were each active in thinning the flowers of the cultivated fruit trees. Flower-thinning agent comprising the above-mentioned compounds as the active component are disclosed in the specifications of European Patent Publication No. 0089205 A2 (published on Sept. 21, 1983) and U.S. Ser. No. 473,354. 
     We have further investigated in an attempt to find out other chemical compounds which are effective in the thinning of flowers and fruit and we have now found that cholesterol is active as a flower-thinning agent. 
     DETAILED DESCRIPTION OF THE INVENTION 
     According to an aspect of this invention, therefore, there is provided a new flower-thinning agent comprising as the active component an effective amount of cholesterol, in association with a suitable liquid or solid carrier for the active component. 
     According to a further aspect of this invention, there is provided a method for thinning flowers of cultivated fruit trees, which comprises applying to the flowers and/or to the body of the fruit trees an effective amount of cholesterol. 
     This invention also includes use of cholesterol as a flower-thinning agent. 
     The flower-thinning agent according to this invention is applied to a fruit tree on the flowering time. The flower-thinning agent of this invention may be applied to a wide variety of fruit trees such as, for example, pear, peach, persimmon, apple, cherry and so on. 
     The flower-thinning agent according to this invention may be formulated into various form such as a solution, wettable powder, emulsion or spray, by mixing with any suitable solid or liquid carrier such as water. It is preferable that the thinning agent is applied in the form of an aqueous emulsion or dispersion of cholesterol as the active component. Such an aqueous emulsion or dispersion of cholesterol may be prepared using surface-active esters of sorbitol with a fatty acid, esters of polyhydric alcohol with a fatty acid, or lecithin as a dispersing agent. 
     The time of application of the flower-thinning agent of this invention may be chosen to be conducted either before or after the spontaneous or artificial pollination of the flowers, so that the flower-thinning effect obtained will reach a desired extent. Besides, the concentration of the cholesterol in the thinning agent as applied may also be chosen appropriately so that the flower-thinning effect obtained will reach a desired extent according to the nature of the fruit tree as treated. 
     The concentration of the cholesterol in the thinning agent may vary, in general, depending on the nature of the fruit tree treated and also on the environmental conditions when the agent is applied, but the concentration of cholesterol is usually in a range of 0.005 to 1.0% by weight, preferably, 0.005 to 0.02% by weight and especially 0.01 to 0.02% by weight. 
     The flower thinning agent according to this invention may be applied at a rate of 80 to 120 l, usually, 100 l per 10 ares of a place where the fruit trees to be treated are planted. 
     The flower-thinning agent according to this invention may optionally contain one or more of plant serols, such as for example, sitosterol, campesterol, stigmasterol and brassicasterol, in combination with the cholesterol. 
     The flower-thinning agent according to this invention has the following advantageous characteristics: 
     (1) The agent of this invention does not exhibit the flower-thinning effect against those flowers of which the fertilization has been finished, and thus it is possible to select the class of fruit trees from which the flowers are to be removed by the thinning treatment, if one choose the time when the agent is applied. 
     (2) The agent of this invention has no phytotoxicity to the plant to which it is applied. 
     (3) The agent of this invention may effectively be applied to a wide variety of fruit trees. 
     (4) The agent of this invention has no toxicity against humans and does not cause any environmental pollution. 
     (5) The agent of this invention is inexpensive. 
     The following Examples illustrate the invention. 
    
    
     EXAMPLE 1 
     An emulsion of 1% (by weight) of cholesterol in water was prepared by mixing together 1 part (by weight) of cholesterol, 15 parts of soya lecithin, 20 parts of ethyl acetate, 13 parts of stearic acid monoglyceride and 51 parts of water. 
     The emulsion as thus obtained was diluted with water to form an emulsion preparation containing the cholesterol at a desired, particular concentration. 
     EXAMPLE 2 
     An aqueous emulsion containing 2% (by weight) of a mixture of cholesterol and plant sterols comprising 50% (by weight) of β-sitosterol, 28% of campesterol, 15% of stigmasterol and 7% of brassicasterol (ratio by weight of cholesterol to the plant sterols=80/20) was prepared by mixing together 2 parts (by weight) of the mixture of cholesterol and plant sterols, 15 parts of soya lecithin, 10 parts of stearic acid monoglyceride, 20 parts of ethyl acetate and 53 parts of water. The resultant emulsion was diluted with water to form an emulsion preparation of a desired particular concentration of the sterols. (Hereinafter, a preparation containing the mixture of cholesterol and the plant sterols is referred to as &#34;mixed agent&#34; or &#34;cholesterol/sterol agent&#34;). 
     The following Examples illustrate the flower-thinning effects of the thinning agent of this invention. 
     EXAMPLE 3 
     Flower Thinning of Japanese Pear Tree 
     The flower-thinning agents of this invention as prepared according to the foregoing Examples 1 to 2 and containing the active component compounds at a concentration of 0.005 to 0.03% (by weight) were sprayed onto the flowers of Japanese pear trees (Variety: Hou-sui). 
     Said thinning agents as sprayed were applied at a rate of 100l per 10 ares. 
     The thinning effects of the agent applied were estimated by counting the number of all the individual flower bodies initially tested (termed as &#34;number of flowers tested&#34;), the number of flower clusters initially tested, the total number of fructified, individual flower bodies in the flower clusters (termed as &#34;number of fructified flowers&#34;) and the number of the flower clusters of which any individual flower bodies had been fructified (termed as &#34;number of fructified flower clasters) and evaluating &#34;percentage of fruit set&#34; (which means percentages of the total number of the fructified, individual flower bodies in the flower clusters, as calculated on the basis of the total number of the fructified and unfructified individual flower bodies in the flower clusters which were remaining on the tree even after the thinning treatment) and &#34;percentage of bearing clusters&#34; (which means percentages of the number of the flower clusters of which any individual flower body had been fructified, as calculated on the basis of the total number of the flower clusters which were remaining on the tree even after the thinning treatment). 
     Tables 1 to 5 given below show the influences on the flower thinning effects (percentage of fruit set and percentage of bearing cluster) of (a) the concentration of the active component in the emulsion applied, (b) the time of spraying the emulsion and (c) spraying of the emulsion on a flower-bud. 
     The thinning effects were estimated after 30 days after the spraying of the emulsion. 
     
                                           TABLE 1__________________________________________________________________________Influence of the Concentration of Cholesterol on the flower thinningeffect.                Number of   Number of Concentration of          Number of                flower                      Number of                            fructified                                  Percentage                                        PercentageActive the active com-          flowers                clusters                      fructified                            flower                                  of fruit                                        of bearingcomponent ponent (%)          tested                tested                      flowers                            clusters                                  set (%)                                        clusters (%)__________________________________________________________________________Cholesterol  0.005   298   52    159   50    53.3* 96.0 0.01     297   54    138   49    46.5**                                        90.6** 0.02     386   59     60   38    15.6**                                        64.4**Control        368   58    297   58    80.7  100.0(Untreated)    407   54    328   54    80.6  100.0__________________________________________________________________________ *Significance at 5% level. **Significance at 1% level. 
    
     
                                           TABLE 2__________________________________________________________________________Influence of the Concentration of the Mixed Agent (cholesterol/plantsterols: at ratio of80/20 by weight) on the flower thinning effect when applied prior to thepollination               Number of   Number of Concentration         Number of               flower                     Number of                           fructified                                 Percentage                                       PercentageActive of the active         flowers               clusters                     fructified                           flower                                 of fruit                                       of bearingcomponent component (%)         tested               tested                     flowers                           clusters                                 set (%)                                       clusters (%)__________________________________________________________________________Mixed  0.005  173   27    61    21    35/3.sup.a                                       77.8Agent 0.01    199   28    73    23    36.7.sup.a                                       82.1 0.02    160   29    68    26    42.5.sup.a                                       89.7 0.03    191   27    73    24    38.2.sup.a                                       88.9Control       314   62    259   61    82.5.sup.b                                       98.4(Untreated)__________________________________________________________________________ .sup.a,b Statistical treatment is based on Mean separation within column by Duncan&#39;s multiple range test, 5% level. 
    
     
                                           TABLE 3__________________________________________________________________________Influence of Time of Spraying the Mixed Agent (cholesterol/plant sterols:at ratioof 80/20 by weight) on the flower thinning effect (Spray afterPollination). -Time of spraying the              Number of   Number ofmixed agent (0.015%        Number of              flower                    Number of                          fructified                                Percentage                                      percentageactive component        flowers              clusters                    fructified                          flower                                of fruit                                      of bearingconcentration)        tested              tested                    flowers                          clusters                                set (%)                                      clusters (%)__________________________________________________________________________Immediately after        151   34     55   30    36.4.sup.a                                      88.2pollination12 hours after pollination        137   36    113   36    82.5.sup.b                                      100.01 day after pollination        188   37    122   36    64.9.sup.b                                      97.32 days after pollination        179   38    124   37    69.3.sup.b                                      97.43 days after pollination        125   24    86    24    68.8.sup.b                                      100.0Control (untreated)        314   62    259   61    82.5.sup.b                                      98.4__________________________________________________________________________ 
    
     
                                           TABLE 4__________________________________________________________________________Influence the Time of Spraying the Mixed Agent (cholesterol/plantsterols: at ratioof 80/20 by weight) on the flower thinning effect (Spray beforePollination).Time of spraying the              Number of   Number ofmixed agent (0.015%        Number of              flower                    Number of                          fructified                                Percentage                                      Percentageactive component        flowers              clusters                    fructified                          flower                                of fruit                                      of bearingconcentration)        tested              tested                    flowers                          clusters                                set (%)                                      clusters (%)__________________________________________________________________________12 hours before pollination        151   23     54   19    35.8.sup.a                                      82.61 day before pollination        198   29     65   22    32.8.sup.a                                      75.92 days before pollination        172   28    137   27    79.7.sup.b                                      96.4Control (Untreated)        314   62    259   61    82.5.sup.b                                      98.4__________________________________________________________________________ 
    
     
                                           TABLE 5__________________________________________________________________________Influence of Spraying the Mixed Agent (cholesterol/plant sterols: atratioof 80/20 by weight) onto flower-bud, on the flower thinning effect.           Number of   Number of     Number of           flower                 Number of                       fructified                             Percentage                                   PercentageTime of spray     flowers           clusters                 fructified                       flower                             of fruit                                   of bearingof the agent     tested           tested                 flowers                       clusters                             set (%)                                   clusters (%)__________________________________________________________________________1 day before     166   28    160   28    96.4.sup.a                                   100.0Control (Untreated)     314   62    259   61    82.5.sup.b                                    98.4__________________________________________________________________________ 
    
     EXAMPLE 4 
     Flower Thinning of Peach Tree 
     Using the emulsion preparation as prepared according to Example 2, there was evaluated the flower thinning effect on peach tree (variety: Nishiki) of the flower-thinning agent according to this invention. 
     In this Example, the thinning effects of the agent applied were estimated by counting the number of all the individual flower bodies initially tested (namely, &#34;number of flowers tested&#34; as defined before), the number of newly shot branches initially tested, the total number of fructified, individual flower bodies on the newly shot brances (termed as &#34;number of fructified flowers&#34;) and the number of the newly shot brances of which any individual flower bodies had been fructified (termed as &#34;number of fructified, newly shot brances&#34;) and evaluating &#34;percentage of fruit set&#34; (which means percentages of the total number of the fructified, individual flower bodies on the newly shot branches, as calculated on the basis of the total number of the fructified and unfructified individual flower bodies on the newly shot branches and &#34;percentage of bearing, newly shot branches&#34; (which means percentages of the number of the newly shot branches of which any individual flower body had been fructified, as calculated on the basis of the total number of the newly shot branches). 
     The thinning effects were estimated 30 days after the spraying of the emulsion. 
     Test results obtained are shown in Tables 6 and 7. Table 6 shows influence of the concentration of the mixed agent (ratio by weight of cholesterol/plant sterols: 80/20) on the thinning effect. Table 7 shows the thinning effect of the mixed agent which was applied after the pollination. 
     
                                           TABLE 6__________________________________________________________________________Influence of the concentration of the mixed agent on the flower thinningeffect.         Number of   Number of   PercentageConcentration   Number of         newly shot               Number of                     fructified                           Percentage                                 of bearingof the active   flowers         branches               fructified                     newly shot                           of fruit                                 newly shotcomponent (%)   tested         tested               flowers                     branches                           set (%)                                 branches (%)__________________________________________________________________________0.005   301   38    116   38    38.5.sup.a                                 100.00.01    243   35    125   33    51.4.sup.ab                                 94.30.02    275   35    116   33    42.4.sup.a                                 94.3Control 258   33    169   32    65.5.sup.b                                 97.0(Untreated)__________________________________________________________________________ 
    
     
                                           TABLE 7__________________________________________________________________________Influence of the mixed agent when applied afterthe pollination on the flower thinning effect.               Number of   Number of   PercentageTime of the spray of the         Number of               newly shot                     Number of                           fructified                                 Percentage                                       of bearingmixed agent (0.015% active         flowers               branches                     fructified                           newly shot                                 of fruit                                       newly shotcomponent concentration)         tested               tested                     flowers                           branches                                 set (%)                                       branches (%)__________________________________________________________________________1 day after pollination         105   24    58    22    55.2.sup.a                                        91.72 days after pollination          72   12    56    12    77.8.sup.b                                       100.03 days after pollination          73    9    52     9    71.2.sup.b                                       100.0Control (Untreated)         258   33    169   32    65.5.sup.b                                        97.0__________________________________________________________________________ 
    
     EXAMPLE 5 
     Flower Thinning of Apple Trees 
     The emulsion preparations as prepared according to the Example 1 above and containing cholesterol as the active agent at a concentration of 0.01 to 0.04% (by weight) were sprayed onto the flowers of apple trees (Variety: Orin). 
     The tests of this Example were carried out sucessively for 3 days at the beginning of May. 
     In this Example, the thinning effects of the agent applied were estimated by evaluating &#34;percentage of fruit set in respect to lateral flowers&#34;, which means percentage of the total number of fructified lateral flower bodies in the flower clusters tested, as calculated on the basis of the total number of fructified and unfructified lateral flower bodies in the flower clusters tested which were remaining on the trees even after the thinning treatment, and also by evaluating &#34;percentage of fruit set in respect to central flowers&#34;, which means percentage of the total number of fructified central flower bodies in the flower clusters tested, as calculated on the basis of the total number of the fructified and unfructified central flower bodies in the flower clusters tested which were remaining on the trees after the thinning treatment. 
     The thinning effects were estimated 30 days after the spray of the thinning agent. 
     The test results are shown in the Table 8. 
     
                                           TABLE 8__________________________________________________________________________        Concentration                Percentage of Fruit Set (%)Time of Spray of Flower        of Active                Lateral Flower of                         Central Flower ofThinning Agent        Component (%)                Flower Cluster                         Flower Cluster__________________________________________________________________________2 days after full bloom        0.04    43.2     78.2of central flower.        0.02    67.5     87.5(Manual pollination was        0.01    76.9     96.8effected 2 hours beforespraying).3 days after full bloom        0.04    77.5     88.2of central flower.        0.02    42.5     88.5(Manual pollination was        0.01    65.0     91.2effected 1 day beforespraying).4 days after full bloom        0.04    87.5     92.9of central flower.        0.02    76.3     95.8(Manual pollination was        0.01    87.5     91.0effected 2 days beforespraying).Control (Untreated)  80.0     98.4__________________________________________________________________________ 
    
     From the Table 8, it is evident that remarkable thinning effects can be obtained when the thinning agent is sprayed 2 days after the full bloom of central flowers. Particularly, the percentages of fruit set in respect to lateral flowers are lowered when the active component is applied at concentrations of 0.02% and 0.04%. 
     The percentages of fruit set in respect to the lateral flowers are lowered also when the thinning agent is applied 3 days after the full bloom of the central flowers. 
     However, no thinning effect can be obtained when the thinning agent is applied 4 days after the full bloom of the central flowers and 2 days after the pollination.