Abstract:
Disclosed is a method for producing Phalaenopsis orchid clone plants, which comprises cutting the tip of a growing root of a Phalaenopsis orchid that has been prepared under sterile conditions at a length of from 1 to 5 mm to prepare a root tip for culture having said predetermined length, cultivating said root tip in a PLB-inducing medium under sterile conditions to thereby induce PLB therein, further cultivating said PLB in a propagating medium, and then re-differentiating said PLB in a re-differentiation medium. The method is practicable and stably given PLB of Phalaenopsis orchids.

Description:
FIELD OF THE INVENTION 
     The present invention relates to a method for producing Phalaenopsis clone plants through root tip culture, and more precisely, to a method for stably mass-producing Phalaenopsis clone plants through root tip culture. 
     BACKGROUND OF THE INVENTION 
     Phalaenopsis attract a great deal of public attention. For cultivation of plants, recently, mass-production of plants through clonal propagation is being in full flood. To the induction of protocorm-like bodies (PLB) that are in the initial stage for the production of clonal plants, at present, applied are conventional leaf segment culture and also other spike-axillary bud culture and root tip culture (M. Tanaka, 1987, Studies on the Clonal Propagation of Phalaenopsis through in-vitro Culture, Memoirs of Faculty of Agriculture, Kagawa University, No. 49; 1-85; S. Ichihashi, 1992, Micropropagation of Phalaenopsis through the Culture of Lateral Buds from Young Flower Stalks, Lindleyana, 7(4): 208-215; M. Kobayashi, M. Komatsuda &amp; S. Yoneuchi, 1990, Studies on the vegetative propagation of Phalaenopsis through root tip culture, J. J. Soc. Hort. Sci., 63(suppl.2); 664-671). 
     However, in the process of the induction of PLB through such known root tip culture (M. Kobayashi, M. Komatsuda &amp; S. Yoneuchi, 1990, Studies on the vegetative propagation of Phalaenopsis through root tip culture, J. J. Soc. Hort. Sci., 63(suppl.2); 664-671) or any other culture, the degree of the intended induction is often low or, as the case may be, no induction is attained for some varieties, hybrids and materials. 
     Because of such unsure induction of PLB, mass-production of plants through clonal propagation could not apply to some varieties and hybrids of Phalaenopsis. Therefore, in order to improve the efficiency in the induction of PLB, it is necessary to establish an effective method of initial culture capable of overcoming the difference in varieties and hybrids and the difference in materials. 
     The reasons for such unsure induction of PLB in known root tip culture are believed to be essentially that the surface of the meristematic tissue of a root tip, which is a material of a PLB-forming source, will be often damaged while being sterilized, and that said tissue could not satisfactorily display its ability for cell division due to conditions and methods unsuitable for cultivating it thereby resulting in that its ability to form PLB is lowered. 
     SUMMARY OF THE INVENTION 
     The object of the present invention is to solve the above-mentioned problems and to provide a practicable and stable method for inducing PLB of Phalaenopsis orchids through root tip culture. 
     The present inventor has assiduously studied root tip culture of Phalaenopsis orchids and, as a result, has found that, when a root tip as cut out of the tip of a root to have a predetermined length is used, PLB can be formed to an elevated degree. After further studies on the method for processing said root tip, the media for PLB induction from said root tip and also the conditions for pre-culture of said root tip, the inventor has at last developed a practicable method for induction of PLB of Phalaenopsis orchids, and has completed the present invention. 
     Specifically, the present invention is a method for producing Phalaenopsis orchid clone plants, which comprises cutting the tip of a growing root of a Phalaenopsis orchid that has been prepared under sterile conditions at a length of from 1 to 5 mm to prepare a root tip for culture having said predetermined length, cultivating said root tip In a PLB-inducing medium under sterile conditions to thereby induce PLB therein, further cultivating said PLB in a propagating medium, and then re-differentiating said PLB in a re-differentiation medium. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     FIG. 1 shows one embodiment of preparing a root tip of a Phalaenopsis orchid to be subjected to root tip culture according to the present invention, in which 1A indicates the way of cutting a root, 1B is a root tip obtained, and 1C is a notched root tip. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Now, the present invention is described in detail hereinunder. 
     Varieties and hybrids of Phalaenopsis orchid for use in the present invention are not specifically defined. For example, employable herein are Phalaenopsis orchids of the genus Doritaenopsis, such as Dtps. Odoriko, Dtps. Zuma Headliner, and Dtps. White Wondern; and those of the genus Phalaenopsis, such as Phal. Orchid World, Phal. Zuma&#39;s Pixie, and Phal. Alfenso Morenon. 
     In the present invention, any of the above-mentioned hybrids and even any other different varieties and hybrids of Phalaenopsis orchid can be used to effectively induce PLB. 
     The growing root of a Phalaenopsis orchid as referred to herein, which is prepared under sterile conditions, may include, for example, growing roots of plants which are cultivated under ordinary sterile conditions, those of spike-axillary bud-derived plants which are cultivated under ordinary sterile conditions, and those of plants growing in greenhouses. The growing roots of plants as cultivated under sterile conditions are preferred to those of plants as grown in greenhouses, as they can be directly used herein without being subjected to sterilization of their surfaces and, therefore, they are not damaged with such surface sterilization. For the growing roots of plants as grown in greenhouses, they shall be used after having been subjected to sterilization of their surfaces according to known methods (for example, see M. Kobayashi, M. Komatsuda &amp; S. Yoneuchi, 1990, Studies on the vegetative propagation of Phalaenopsis through root tip culture, J. J. Soc. Hort. Sci., 63(suppl.2); 664-665). 
     The root of a Phalaenopsis orchid thus prepared is cut at a length of from 1 to 5 mm, preferably from 2 to 4 mm, from its tip, using a sterile knife to give a root tip for culture. If the length of the root tip is smaller than the lowermost limit, many such root tips will die, resulting in the decrease in the survival rate of root tip. On the other hand, if too long root tips are used, the degree of PLB formation will be low though their survival rate will be high. 
     The degree of PLB formation will be elevated effectively, if the top of the root tip for culture is notched to a depth of from 0.5 to 2.0 mm, preferably to a depth of about 1/2 of the length of said root tip, depending on the length thereof (see FIG. 1). 
     Next, the thus-processed root tip for culture is placed on a PLB-inducing medium with its cut surface being kept in contact with the medium. 
     As the PLB-inducing medium, usable are any ordinary media for plant tissue culture. For example, used herein is MS medium or 1/3 MS medium. Preferably, the PLB-inducing medium may contain any saccharide of, for example, polysaccharides, monosaccharides and sugar alcohols (e.g., sucrose, sorbitol). For sucrose, its content in the medium may be from 0.5 to 3%, preferably 0.5%. For sorbitol, its content therein may be from 0.05 to 0.5%, preferably 0.1%. The addition of sorbitol to the medium may increase the degree of PLB induction and also the survival rate of root tip being cultivated. 
     Moreover, the addition of plant hormones to the PLB-inducing medium is more advantageous. For plant hormones, auxins such as naphthalene-acetic acid (NAA) may be added to the medium in an amount of from 0.005 to 0.05 ppm, preferably 0.01 ppm; or cytokinins such as benzyladenine (BA) may be added thereto in an amount of from 1 to 15 ppm, preferably 5 ppm. 
     In the method of the present invention, in general, a gelling agent such as Gellan gum or agar may be used as the support for the medium. For Gellan gum, it may be added to the medium in an amount of from 0.2 to 0.4%, preferably from 0.25 to 0.3%. 
     The induction culture for PLB may be conducted in any ordinary manner. In general, for example, root tips are cultivated at from 20° to 28° C. preferably at 25° C. for from 30 to 60 days, while being exposed to light (at an illuminance of from 500 to 5000 lux, preferably 3000 lux) continuously or for 16 hours a day. 
     To induce PLB, low-temperature culture is preferred in the initial stage of cultivating root tips. For example, prior to being cultivated under the above-mentioned ordinary conditions, root tips are preferably pre-cultivated at low temperatures of from 5° to 15° C., preferably at 10° C. for from 8 to 72 hours, preferably for about 12 hours, while being exposed to light under the same conditions as for such ordinary culture, to produce better results. 
     As a result of said induction culture of root tip for PLB, PLB are formed. The ability of root tips to form PLB varies, depending on the varieties and hybrids of Phalaenopsis orchid from which said root tips are derived. Therefore, the cultivation of root tips shall be continued for an appropriate period of time. 
     Next, to regenerate the plants of a Phalaenopsis orchid from PLB thus induced from the root tip of the Phalaenopsis orchid through the culture of said root tip, PLB may be transplanted into ordinary sterile media, in which PLB may grow with ease to give the intended plants. In general, one PLB grows to give one plants. Therefore, in order to mass-produce a large number of the intended plants, PLB must be propagated. For this, in order to facilitate the re-differentiation of PLB into plants, the culture environment for the propagation of PLB, which includes, for example, the degree of lighting and that of aeration, must be kept all the time constant. 
     In the present invention, PLB as induced from root tip of a Phalaenopsis orchid are cultivated in a propagation medium, and thereafter said PLB are re-differentiated in a re-differentiation medium to obtain plants of said Phalaenopsis orchid. 
     The PLB propagation medium for use in the present invention may be any ordinary medium that is generally used for ordinary propagation of PLB. Concretely, it may include, for example, MS media. Preferred are Tanaka&#39;s V &amp; W-modified media (M. Tanaka, 1987, Studies on the Clonal Propagation of Phalaenopsis through in-vitro Culture, Memoirs of Faculty of Agriculture, Kagawa University, No. 49; 1-85). Regarding the conditions for propagating PLB, PLB may be cultivated and propagated at from 20° to 28° C., preferably from 23° to 26° C., while being exposed to light at an illuminance of from 200 to 10000 lux, preferably 2000 lux, for from 8 to 24 hours a day, preferably for 16 hours a day. 
     The re-differentiation medium for use in the present invention may be any ordinary one that is generally used for ordinary re-differentiation of PLB. Concretely, it may include, for example, MS media. Preferred embodiments of the media are the present inventor&#39;s V &amp; W-modified media (T. S. Zhou, 1995, in-vitro Culture of Doritaenopsis: Comparison Between Formation of Hyperhydric Protocorm-like-body (PLB) and the Normal PLB., Plant Cell Reports, 15: 181-185). The conditions for the intended re-differentiation may be the same as those mentioned hereinabove. 
     Now, the present invention is described in detail by means of the following Examples, which, however, are not intended to restrict the scope of the invention. 
     EXAMPLE 1 
     Growing roots derived from plants of Dtps. Odoriko as cultivated according to spike-axillary bud culture were used herein as samples. For the preparation and cultivation of the spike-axillary buds of Dtps. Odoriko, referred to was a Tanaka method (M. Tanaka, 1987, Studies on the Clonal Propagation of Phalaenopsis through in-vitro Culture, Memoirs of Faculty of Agriculture, Kagawa University, No. 49: 1-85). 
     The roots were cut at a length of 1 mm, 2 mm and 5 mm from their tips to prepare root tips to be cultivated herein. Apart from these, also prepared herein other root tips of 2 mm long, which were notched at their tops to have a notch of about 1.0 mm in depth. 0.5% of sucrose and 0.4% of Gellan gum were added to a 1/3 MS medium to prepare a medium for cultivation of the root tips. The root tips were put on this medium and cultivated at 25° C., while being exposed to light at 3000 lux for 16 hours a day. After 2 months, the root tips were checked. The results obtained herein are shown in Table 1 below. 
     
                       TABLE 1______________________________________Length Number of          Number of                   Percentage of                            Number of                                    Survivalof Root Root     PLB      PLB      Living Root                                    RateTips  Tips     Formed   Formation                            Tips    (%)______________________________________1 min 20       4         20%     4       202 min 20       5        25       10      505 min 20       3        15       17      85Notched 20       7        35       10      50______________________________________ 
    
     As in Table 1 above, the survival rate in the group of root tips of 2 mm long was about 50%, and the percentage of PLB formation was increased in said group. In particular, the percentage of PLB formation was significantly increased in the group of notched root tips. 
     EXAMPLE 2 
     Growing roots derived from plants of Dtps. Odoriko as cultivated according to spike-axillary bud culture were used herein as samples. The spike-axillary buds of Dtps. Odoriko were prepared and cultivated in the same manner as in Example 1. 
     The roots were cut at a length of 2 mm from their tips to prepare root tips to be cultivated herein, which were notched at their tops to have a notch of about 1.0 mm in depth. 
     Three media were prepared herein for cultivation of the root tips. The first is a medium a, which was prepared by adding 0.5% of sucrose and 0.4% of Gellan gum to a 1/3 MS medium; the second is a medium b, which was prepared by adding 0.5% of sucrose, 0.1% of sorbitol and 0.4% of Gellan gum to a 1/3 MS medium; and the third is a medium c, which was prepared by adding 0.5% of sucrose, 0.1% of sorbitol, 0.01 ppm of NAA, 5 ppm of BA and 0.4% of Gellan gum to a 1/3 MS medium. The root tips were put on any of these media and cultivated at 25° C., while being exposed to light at 3000 lux for 16 hours a day. After 2 months, the root tips were checked. The results obtained herein are shown in Table 2 below. 
     
                       TABLE 2______________________________________ Number of          Number of                   Percentage of                            Number of                                    Survival Root     PLB      PLB      Living Root                                    RateMedium Tips     Formed   Formation                            Tips    (%)______________________________________a     40       12        30%     18      45b     40       17       43       20      50c     40       26       65       33      83______________________________________ 
    
     As in Table 2 above, the addition of plant hormones such as NAA and BA to the medium along with sorbitol resulted in the noticeable increase in the survival rate and the percentage of PLB formation. 
     EXAMPLE 3 
     Growing roots derived from plants of Dtps. Odoriko as cultivated according to spike-axillary bud culture were used herein as samples. The spike-axillary buds of Dtps. Odoriko were prepared and cultivated in the same manner as in Example 1. 
     The roots were cut at a length of 2 mm from their tips to prepare root tips to be cultivated herein, which were notched at their tops to have a notch of about 1.0 mm in depth. 
     0.5% of sucrose, 0.1% of sorbitol, 0.01 ppm of NAA, 5 ppm of BA and 0.4% of Gellan gum were added to a 1/3 MS medium to prepare a medium for cultivation of the root tips. The root tips were put on this medium and pre-cultivated under various conditions (at from 5° to 15° C. for from 12 to 72 hours), while being exposed to light at 3000 lux, and thereafter further cultivated at 25° C. in an ordinary manner, while being exposed to light at 3000 lux for 16 hours a day. After 2 months, the root tips were checked. The results obtained herein are shown in Table 3 below. The samples in the control group were not pre-cultivated but were directly cultivated at 25° C. with exposure to light at 3000 lux for 16 hours a day, and checked after 2 months. 
     
                                           TABLE 3__________________________________________________________________________Temperature  Time for              Number ofin Pre-  Pre-culti-       Number             Number                  Percentage                        Living                             Survivalcultivation  vation       of Root             of PLB                  of PLB                        Root Rate(°C.)  (hr) Tips  Formed                  Formation                        Tips (%)__________________________________________________________________________ 5     12   10    4     40%  6    60  24   10    1    10    5    50  72   10    0     0    1    1010     12   10    7     70%  8    80  24   10    6    60    8    80  72   10    1    10    4    4015     12   10    5     50%  7    70  24   10    5    20    8    80  72   10    2    20    8    80Control  --   10    6    60    7    70__________________________________________________________________________ 
    
     As in Table 3 above, the root tips of the group that had been pre-cultivated at a low temperature of 10° C. for 12 hours gave an increased percentage of PLB formation and an increased survival rate, as compared with those of the other groups. 
     As has been described in detail hereinabove with reference to its preferred embodiments, the present invention increases the percentage of the formation of PLB of Phalaenopsis orchids and also the survival rate of root tips of Phalaenopsis orchids, while increasing the degree of regeneration of plants of Phalaenopsis orchids. Thus, it is expected that the present invention contributes to a high degree to overcoming the problems to be caused by the difference in the varieties and hybrids of Phalaenopsis orchids in the production of clonal plants of Phalaenopsis orchids. 
     The entire disclosure of Japanese Patent Application No. 8-104743 filed on Apr. 3, 1996 including specification, claims and summary are incorporated herein by reference in its entirety.