AU2021301453A1 - Improved methods of grafting plants - Google Patents

Abstract

The present invention relates generally to the fields of horticulture and agriculture, and particularly to the production of plants using grafting techniques. In one form, the invention relates to a method for producing a grafted plant, including providing a plant rootstock portion, a plant scion portion comprising bud tissue, and a plant interstock portion. The plant interstock portion is disposed between, and makes contact with both the plant rootstock portion and the plant scion portion such that a functional union is formed between (i) the plant rootstock portion and the plant interstock portion and (ii) the plant interstock portion and the plant scion portion. A particularly preferred plant scion is obtained from a plant of the genus

Description

IMPROVED METHODS OF GRAFTING PLANTS

5 FIELD OF THE INVENTION

[001]. The present invention relates generally to the fields of horticulture and agriculture, and particularly to the production of plants using grafting techniques. 0 BACKGROUND TO THE INVENTION

[002]. It is known in the arts of horticulture and agriculture to graft together two or more plant portions of different species to form a grafted plant. After grafting, the so-formed plant continues to grow into a mature plant. Grafting is used extensively in commercial5 settings for the asexual propagation of plants.

[003]. Typically, the “scion” of a first species is grafted onto the tmnk of a “rootstock” of a second species. The scion portion forms the upper part of the grafted plant and is selected for some advantageous feature such as the production of high quality fruit or an0 aesthetically pleasing flower. On some occasions, scions from multiple species or varieties may be grafted onto a single rootstock so as to, for example, produce a tree bearing two or more fruit species or varieties.

[004]. The rootstock may be chosen for vigour, hardiness, disease resistance, water5 tolerance, or to restrict tree height for example. Generally, the rootstock is grown for at least a year before grafting is performed.

[005]. For a successful graft, the vascular cambium tissues of the rootstock and scion portions must make physical contact with each other such that a functional union between0 the vascular cambium of each tissue is established. Generally, non-vascular structural tissues of the scion and rootstock do not form any useful union. [006]. As is well understood by the skilled artisan, it cannot be expected that any scion/rootstock combination can be successfully grafted. Generally, the higher the genetic relatedness of the scion and rootstock, the more likely a functional graft union will form. The success rate is typically low when grafting is attempted between plants of the same

5 family but from different genera. Grafting between different families is rarely successful. In that sense, the scion and rootstock are said to be “incompatible”.

[007]. In some instances, a scion/rootstock combination forms a functional plant at first instance, however the viability of the plant decreases time until its economic value is lost,0 or it dies. Such combinations could nevertheless be considered incompatible given that the union fails or is compromised albeit after the elapse of some time. In some cases the incompatibility may not be apparent for at least five or ten years. Whatever the time frame, failure of a grafted plant is to be avoided given the economic costs associated with removal and replacement with a new plant. 5

[008]. Where a scion is incompatible with a rootstock, an “interstock” portion of a third plant may be used. The interstock portion is capable of forming a functional union with both the rootstock and scion portions such that an indirect vascular connection is formed between the scion and rootstock. While the prior art provides various methods for0 interstock-mediated grafting, such methods can present one or more problems.

[009]. A first problem may arise for grafting methods requiring “bark slip”, i.e. the bark of the rootstock being readily separable from the underlying tissues to form a bark flap. In such methods the interstock and part of the scion are maintained under the bark flap. While5 generally effective, some expertise is required to carefully peel away the bark in a manner that does not unduly damage underlying tissues and to form a recess that is appropriately sized and shaped so as to snugly receive the interstock and scion portions.

[010]. A second problem may arise in that bark slip presents only during certain windows0 of time in the rootstock growth cycle, thereby prohibiting year-round production of grafted plants. [Oil]. A third problem may arise for bark slip reliant methods in that only rootstocks having a relatively large diameter tmnk may be useful, thereby excluding the use of smaller rootstock seedlings. It can be difficult, if not impossible, to provide bark flaps of sufficient

5 size to retain the interstock and scion portions for rootstocks having a small diameter tmnk.

[012]. A fourth problem may arise in that a bark flaps may overlie some or all of the interstock. The flaps may also overlie some or all of the interface between the interstock and the scion portions, and/or some or all of the interface between the interstock and the0 rootstock portions. In such circumstances the overlying preventing or inhibiting visual assessment that the graft has successfully taken.

[013]. A fifth problem may arise in that for certain combinations of incompatible scion and rootstock, complex methods and/or extended nursery time is required to overcome the5 incompatibility. A commercially important example presents in grafting certain citms varieties to the trifoliate orange ( Poncirus trifoliata ) rootstock. One such citms variety is the “Imperial” variety of mandarin which, if grafted to trifoliate orange rootstock results in a tree of limited lifespan (typically less than ten years). That problem is overcome in the art at present by a multi-step process requiring the grafting of a compatible scion, allowing0 that scion to grow and then grafting the incompatible scion to a stem of the grown compatible scion. This multi-step procedure adds considerable nursery time and associated expense in the production of an Imperial mandarin tree.

[014]. A sixth problem may arise where a grafted scion has not taken successfully to the5 rootstock. In such a circumstance, the rootstock is wasted or may need to be re grafted.

[015]. Any of the first, second, third, fourth, fifth or sixth problems may present solus, and the present invention (in one or more embodiments) overcomes or ameliorates that problem. In some circumstances, any combination of two, three, four or five of the first,0 second, third, fourth, fifth and sixth problems may present and the present invention (in one or more embodiments) overcomes or ameliorates such combination. All six of the first, second, third, fourth, fifth and sixth problems may present and the present invention (in one or more embodiments) overcomes or ameliorates all six problems.

[016]. In some circumstances, the present invention (in one or more embodiments)

5 provides an improvement to a prior art grafting method, whether or not the improvement is in respect of any of the first, second, third, fourth, fifth or sixth problems. In other circumstances, the invention (in one or more embodiments) provides no improvement whatsoever over any prior art and instead merely provides a useful alternative to the prior art. 0

[017]. The discussion of documents, acts, materials, devices, articles and the like is included in this specification solely for the purpose of providing a context for the present invention. It is not suggested or represented that any or all of these matters formed part of the prior art base or were common general knowledge in the field relevant to the present5 invention as it existed before the priority date of each claim of this application.

SUMMARY OF THE INVENTION 0 [018]. In a first aspect, but not necessarily the broadest aspect, the present invention provides a method for producing a grafted plant, the method comprising the steps of: providing a plant rootstock portion, a plant scion portion comprising bud tissue, and a plant interstock portion; disposing the plant interstock portion between the plant rootstock portion and the plant scion portion such that the plant interstock portion is contacted with5 the plant rootstock portion and the plant interstock portion; wherein the plant rootstock, interstock and scion portions are prepared, and the steps of disposing and contacting are performed such that a functional union is formed between (i) the plant rootstock portion and the plant interstock portion and (ii) the plant interstock portion and the plant scion portion. 0 [019]. In one embodiment of the first aspect, the plant scion portion is obtained from a plant of the genus Citrus.

[020]. 3 In one embodiment of the first aspect, the plant of the genus Citrus is Citrus

5 reticulata.

[021]. In one embodiment of the first aspect, the plant rootstock portion is incapable of forming sufficient functional union with the plant scion portion such that the grafted plant is viable for at least 1, 2, 3, 4, 5, 6, 7, 8, 9 or 10 years. 0

[022]. In one embodiment of the first aspect, the plant rootstock portion is incapable of forming sufficient functional union with a scion obtained from Citrus reticulata such that the grafted plant is viable for at least 1, 2, 3, 4, 5, 6, 7, 8, 9 or 10 years. 5 [023]. In one embodiment of the first aspect, the plant rootstock portion is obtained from a plant of the genus Poncirus.

[024]. In one embodiment of the first aspect, the plant of the genus Poncirus is Poncirus trifoliata. 0

[025]. In one embodiment of the first aspect, the plant interstock portion isobtained from a Citrus x sinensis plant.

[026]. In one embodiment of the first aspect, a portion of the plant rootstock portion has5 been removed to expose a region configured to contact and form a functional union with a surface of the plant interstock portion and the plant scion portion.

[027]. In one embodiment of the first aspect, the method comprises mobilising a region of bark of the plant rootstock portion so as to accommodate the plant interstock portion and/or0 the plant scion portion such that the mobilised region of bark overlies a region of the plant interstock portion and/or a region of the plant scion portion. [028]. In one embodiment of the first aspect, the plant interstock portion comprises or is devoid of bud tissue.

5 [029]. In one embodiment of the first aspect, the rootstock is devoid of a region of bark which has been mobilized and/or the method is devoid of the step of mobilising a region of bark of the plant rootstock portion.

[030]. and/or the method is devoid of the step of mobilising a region of bark of the plant0 rootstock portion the method comprises removing a portion of the bark of the plant rootstock portion so as to provide a contact surface configured to contact and form a functional union with the plant interstock portion and/or the plant scion portion.

[031]. In one embodiment of the first aspect, the contact surface of the plant rootstock5 portion is configured to contact the plant interstock portion and/or the plant scion portion is elongate and a surface of the plant interstock portion and/or the plant scion portion is configured to contact the contact surface is elongate.

[032]. In one embodiment of the first aspect, the plant interstock portion comprises (i) a0 first contact surface configured to contact and form a functional union with a contact surface of the plant rootstock portion, and (ii) a second contact surface configured to contact and form a functional union with a contact surface of the plant scion portion.

[033]. In one embodiment of the first aspect, the first contact surface is adjacent to the5 second contact surface.

[034]. In one embodiment of the first aspect, the plant interstock portion comprises bud tissue. 0 [035]. In one embodiment of the first aspect, the bud tissue extends from a position below the second contact surface. [036]. In one embodiment of the first aspect, the method comprises the steps of causing or allowing a bud shoot to form from the bud tissue of the plant interstock portion to burst and then removing the bud shoot.

5

[037]. In one embodiment of the first aspect, the method comprises the step of applying binding means to maintain contact between (i) the plant rootstock portion and the plant interstock portion and (ii) the plant interstock portion and the plant scion portion. 0 [038]. In a second aspect, the present invention provides a plant interstock portion for producing a grafted plant, the plant interstock portion comprising an inward facing surface configured to contact and form a functional union with a plant rootstock portion, a first outwardly directed contact surface configured to contact and form a functional union with a contact surface of the plant scion portion, and (ii) a second outwardly directed surface5 that is incapable of contacting and forming a functional union with a contact surface of the plant scion portion.

[039]. In one embodiment of the second aspect, the plant interstock portion is elongate. 0 [040]. In one embodiment of the second aspect, the first outwardly directed contact surface is positioned above or below the second outwardly directed surface.

[041 ]. In one embodiment of the second aspect, the plant interstock portion comprises bud tissue. 5

[042]. In one embodiment of the second aspect, the bud tissue extends from the second outwardly directed surface.

[043]. In one embodiment of the second aspect, the plant interstock portion is compatible0 with a plant scion portion of the genus Citrus such as Citrus reticulata and also a rootstock portion of the genus Poncirus such as Poncirus trifoliate. [044]. In a third aspect, the present invention provides a grafted plant produced from a plant rootstock portion, a plant interstock portion and a plant scion portion, wherein a functional union has formed or in the process of forming between (i) the plant rootstock

5 portion and the plant interstock portion and (ii) the plant interstock portion and the plant scion portion.

[045]. In one embodiment of the third aspect, the plant scion portion is obtained from a plant of the genus Citrus. 0

[046]. In one embodiment of the third aspect, the plant of the genus Citrus is Citrus reticulata.

[047]. In one embodiment of the third aspect, the plant rootstock portion is incapable of5 forming a functional union with the plant scion portion.

[048]. In one embodiment of the third aspect, the plant rootstock portion is incapable of forming a function union with a scion obtained from Citrus reticulata 0 [049]. In one embodiment of the third aspect, the plant rootstock portion is obtained from a plant of the genus Poncirus.

[050]. In one embodiment of the third aspect, the plant of the genus Poncirus is Poncirus trifoliata. 5

[051]. In one embodiment of the third aspect, the plant interstock portion is a chip configured to be predominantly or completely overlaid by the plant scion portion.

[052]. In one embodiment of the third aspect, a portion of the plant rootstock portion has0 been removed to provide a region which contacts and forms a functional union with a surface of the plant interstock portion. [053]. In one embodiment of the third aspect, the grafted plant comprises a previously mobilised region of bark of the plant rootstock portion which accommodates the plant interstock portion and/or the plant scion portion such that the previously mobilised region

5 of bark overlies a region of the plant interstock portion and/or a region of the plant scion portion.

[054]. In one embodiment of the third aspect, plant interstock portion is devoid of bud tissue. 0

[055]. In one embodiment of the third aspect, the rootstock is devoid of a region of bark which has been previously mobilised.

[056]. In one embodiment of the third aspect, the plant rootstock portion has a portion of5 its bark removed so as to provide a contact surface which contacts and forms a functional union with the plant interstock portion.

[057]. In one embodiment of the third aspect, the contact surface configured to contact the plant interstock portion is elongate and a surface of the plant interstock portion which0 contacts the contact surface is elongate.

[058]. In one embodiment of the third aspect, the plant interstock portion comprises (i) a first outwardly directed contact surface which contacts and forms a functional union with a contact surface of the plant scion portion, and (ii) a second outwardly directed surface5 that is incapable of contacting and forming a functional union with a contact surface of the plant scion portion.

[059]. In one embodiment of the third aspect, the first outwardly directed contact surface is positioned above or below the second outwardly directed surface. 0 [060]. In one embodiment of the third aspect, the plant interstock portion comprises bud tissue and/or a bud shoot.

[061]. In one embodiment of the third aspect, the bud tissue and/or the bud shoot extends from the second outwardly directed surface.

[062]. In one embodiment of the third aspect, a bud shoot has been removed.

[063]. In one embodiment of the third aspect, the bud tissue and/or the stump of a removed bud shoot is callused.

[064]. In one embodiment of the third aspect, the grafted plant comprises binding means which maintains contact between (i) the plant rootstock portion and the plant interstock portion and (ii) the plant interstock portion and the plant scion portion.

[065]. In one embodiment of the third aspect, the plant interstock portion is not partially or fully obscured by a bark portion of the plant rootstock portion.

[066]. In one embodiment of the third aspect, the functional unions formed between (i) the plant rootstock portion and the plant interstock portion and (ii) the plant interstock portion and the plant scion portion are both visible.

[067]. In one embodiment of the third aspect, the grafted plant is produced by the method of any embodiment of the first aspect.

[068]. In a fourth aspect, the present invention provides the combination of the plant interstock portion of any embodiment of the second aspect with a plant rootstock portion and/or a plant scion portion. [069]. In one embodiment of the fourth aspect, the combination comprises the plant interstock portion of any embodiment of the second aspect with a plant rootstock portion and a plant scion portion.

5

BRIEF DESCRIPTION OF THE FIGURES

[070]. FIG. 1 illustrates diagrammatically a preferred method of the present invention whereby an interstock having bud tissue allows for the grafting of a scion to an otherwise0 incompatible rootstock. The diagrams run left to right in accordance with the sequence of the method steps.

[071]. FIG. 2 is a photograph of a rootstock ( Poncirus trifoliata ) grafted to an Imperial mandarin scion using a sweet orange interstock chip having bud tissue. The photograph5 was taken four weeks after budding and with the budding tape removed.

[072]. FIG. 3 is a photograph of a rootstock ( Poncirus trifoliata ) grafted to an Imperial mandarin scion using a sweet orange interstock chip having bud tissue. The photograph was taken after the development of interstock and scion budshoots (around 8 weeks after0 grafting). The top of the rootstock seedling has been removed to force growth of the new interstock and scion budshoots.

[073]. FIG. 4 is a photograph of a rootstock ( Poncirus trifoliata) grafted to an Imperial mandarin scion using a sweet orange interstock chip having bud tissue. The photograph5 was taken after the development of interstock and scion budshoots, and the subsequent removal of the interstock budshoot to leave the scion shoot only.

[074]. Unless otherwise indicated herein, features of the drawings labelled with the same numeral are taken to be the same features, or at least functionally similar features, when0 used across different drawings. [075]. The drawings are not prepared to any particular scale or dimension and are not presented as being a completely accurate presentation of the various embodiments.

5 DETAILED DESCRIPTION OF THE INVENTION AND PREFERRED EMBODIMENTS THEREOF

[076]. After considering this description it will be apparent to one skilled in the art how the invention is implemented in various alternative embodiments and alternative0 applications. However, although various embodiments of the present invention will be described herein, it is understood that these embodiments are presented by way of example only, and not limitation. As such, this description of various alternative embodiments should not be constmed to limit the scope or breadth of the present invention. Furthermore, statements of advantages or other aspects apply to specific exemplary embodiments, and5 not necessarily to all embodiments, or indeed any embodiment covered by the claims.

[077]. Throughout the description and the claims of this specification the word "comprise " and variations of the word, such as "comprising" and "comprises" is not intended to exclude other additives, components, integers or steps. 0

[078]. Reference throughout this specification to “one embodiment” or “an embodiment” or similar terminology means that a particular feature, stmcture or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, appearances of the phrases “in one embodiment” or “in an embodiment”5 or similar in various places throughout this specification are not necessarily all referring to the same embodiment, but may.

[079]. As used herein, the directional terms “outwardly directed” and “inwardly directed” are to be considered with reference to a plant in that “outwardly directed means generally0 toward the environment of the plant, and “inwardly directed” means generally away from the environment of the plant. The relative positional terms “above” and “below” are to be considered with reference to a plant in a normal generally upward growing orientation with roots in a substrate and the remainder of the plant extending generally away from the substrate and toward the sky.

5 [080]. The present invention (in one or more embodiments) is predicated at least in part on the inventor’s discovery that grafting techniques can be performed by methods which do not require bark slip, or the growth of an intermediate scion before grafting of a target scion. In addition or alternatively, the present invention (in one or more embodiments) is predicated at least in part on the inventor’s discovery that the use of a plant interstock0 portion in the form of a chip having bud tissue is useful in producing grafted plants. In addition or alternatively, the present invention (in one or more embodiments) is predicated at least in part on the inventor’s discovery that a Citrus spp scion can be grafted to a Poncirus trifoliata rootstock by the use of a plant interstock portion in the form of a chip, the chip having bud tissue or being devoid of bud tissue. 5

[081 ]. The present invention will now be more fully described by reference to the attached

Figures. It should be understood that any additional, alternative or optional features referred to in the course of the following description of the embodiments of the Figures should not be taken as necessarily linked to all the features of those embodiments. 0

[082]. Turning firstly to FIG. 1, there is shown a series of diagrams showing a preferred method of the present invention.

[083]. The first step is selecting a rootstock, according to any desirable property or any5 advantage it may confer to the resultant grafted plant. A portion of the rootstock tmnk is marked (10).

[084]. The second step is the cutting a portion of bark and underlying tissue from the rootstock trunk (10) to form an elongate cavity having an outwardly facing contact surface0 (15). The removal is effected by use of a sharp blade being urged downwardly along the tmnk in a first cut graduating from shallow to deep. Once the first cut is of sufficient length, a second cut is made toward the bottom, the cut being angled generally downwardly so as to intersect with the first cut thereby excising a portion of the rootstock tmnk (10). The excised portion is discarded. The second cut forms a generally upwardly directed angled contact surface (16), and also a small notch (17) on the rootstock tmnk (10) within

5 which a lower terminal region of the plant interstock portion (100) may sit. The outwardly facing contact surface (15) and upwardly facing contact surface (16) each has exposed cambium vascular elements (including xylem and phloem).

[085]. The third step involves disposing a chip-shaped interstock portion (100) into the0 cavity so as to contact the outward facing contact surface (15) of the rootstock portion (10). Further detail of the interstock portion (100) is shown at FIG. 3, and will be explained at this point of the description given the relevance to the method shown at FIG. 1.

[086]. The interstock portion (100) has been obtained by cutting a bud (105) from a donor5 plant (not drawn) which is compatible with the rootstock. In cutting out the bud (105), an inwardly facing contact surface (110) is formed to expose vascular cambium tissue (not drawn). A generally upwardly facing contact surface (115), and a generally opposed downwardly facing contact surface (116) are formed in the course of cutting out the bud from the interstock donor plant. It will be noted from the drawing of step 3. 0

[087]. In this preferred embodiment the plant interstock portion is obtained from a plant of the genus Citrus, and selected so as to allow for the compatible grafting of the selected plant scion portion to the selected plant rootstock portion. In this preferred embodiment, the plant scion portion is Imperial mandarin ( Citrus reticulata). For that scion, the5 interstock portion should be different (i.e. not Citms reticulata) given the known incompatibility with the Poncirus trifoliata rootstock. In this embodiment, the interstock is a Citrus x sinensis, and particularly a “Valencia” cultivar.

[088]. A scion portion (200) is prepared, and as discussed above is obtained from an0 Imperial mandarin ( Citrus reticulata) plant and contacted with the contact surface (15) of the rootstock portion (10) as shown at the fourth step of FIG. 1. It will be noted from the drawing that the contact surfaces (115) and (215) are shaped and dimensioned so as to mutually complimentary in so far as mutual contact is made across the surfaces (115) and (215).

5 [089]. Further detail of the scion portion (200) is shown at FIG. 3. The scion portion (200) is prepared by cutting a bud (205) from a donor plant (not drawn). In cutting out the bud (205) an inwardly facing contact surface (210) is formed, having exposed vascular cambium tissue (not drawn). An upwardly facing contact surface (215) is further formed in the course of cutting out the bud from the scion plant.. It will be understood from the0 fourth step of FIG. 1 that exposed cambia of the scion portion (200) and interstock portion (100) are brought together by way of abutment of the contact surfaces (115) and (215). The abutment provides the opportunity for a functional union to form such that water and nutrients can flow between the scion portion (200) and the interstock portion (100). It will be understood that water and nutrients may flow also between the rootstock portion (10)5 and the interstock portion (100), and also between the rootstock portion (10) and the scion portion (200). Rather than flow directly between the scion portion (200) and the interstock portion (100), water and nutrients may flow between the scion portion (200) and the interstock portion (100) via the rootstock portion (10). 0 [090]. From the arrangement shown at step four of FIG. 1 it will be understood that the surfaces interfacing with the environment of the rootstock portion (10), the interstock portion (100) and the scion portion (200) are all bark covered and therefore provide protection for the surfaces having exposed cambium tissue (15), (110), (115). 5 [091]. The arrangement shown at step 4 of FIG. 1 is maintained in place by wrapping budding tape thereabout, and the resultant grafted plant being maintained with water, nutrients, light and any other requirements.

[092]. Budding tape is removed after about four weeks, and as shown in FIG. 4 the tissues0 of the rootstock (10), interstock (100) and scion (200) have fused, although lines of demarcation remain, as exemplified by the light coloured boarders apparent about and between the interstock portion (100) and the scion portion (200). As shown in FIG. 2 the budding tissues (105) and (205) have not yet formed bud shoots.

[093]. FIG. 5 shows the situation about eight weeks after grafting, with bud shoots (120)

5 and (220) extending from the interstock portion (100) and scion portion (200) respectively. The upper terminus of the rootstock portion (10) has been removed to stimulate growth of new buds and budshoots. In this situation, the scion has taken well yielding clearly healthy foliage. If for some reason the scion did not take, then the rootstock would not be wasted, and instead grown having the foliage of the interstock 0 a. .

[094]. FIG. 6 shows the situation where the interstock budshoots have been removed, leaving the scion portion budshoots (120). The stump of the removed interstock budshoot is marked (130). The stump (130) will eventually form a callus, leaving only scion stems and foliage on the hybrid tree. 5

[095]. Also clear from FIG. 6 is the demarcation (300) between the scion portion (200) and the interstock portion (100).

[096]. As will be appreciated, the method may be operable whereby the interstock portion0 and scion portions are brought together to form a combination as a first step, with that combination being contacted to the rootstock portion in a second step to form the arrangement as shown in step 4 of FIG. 1.

[097]. The embodiments exemplified in the drawings (and optionally one or more other5 embodiments) overcome the problems associated with the use of grafting methods reliant on bark slip in the rootstock portion. As will be now appreciated, the present methods do not require the mobilisation of any mobilised bark portion to form a flap. As shown at step 2 of FIG. 1, a portion of rootstock bark and some underlying tissue is completely removed by cutting, and discarded with no bark flap being formed. Accordingly, the present method0 may be utilised year-round and having no regard as to whether or not the bark of the rootstock portion is in a state where it is readily separable. [098]. The embodiments exemplified in the drawings (and optionally one or more other embodiments) overcome the problems associated with the use of grafting methods on small diameter rootstock portions. It is difficult or impossible to provide bark flaps of a useful

5 size in such rootstock portions, however with the present methods not requiring bark flaps at all, small diameter rootstocks may be exploited. An advantage may be provided in the relatively immature rootstock plants having short production times may be exploited in the present methods. 0 [099]. The embodiments exemplified in the drawings (and optionally one or more other embodiments) overcome the problems associated with visual obfuscation of the interstock portion and/or any one or more of the grafting unions formed. The absence of any requirement for a bark flap in the present methods means that the entire interstock portion and all graft unions are clearly visible (at least when any tape or other binding means5 present is removed). Accordingly, the nurseryman is able to readily inspect the health of the newly grafted portions, and take corrective action or avoid further time and expense maintaining a failing graft.

[100]. Where the scion portion appears to be failing, then the plant can nevertheless be0 maintained and grown for sale where the interstock portion comprises budding tissue. In that regard, the interstock portion becomes the new scion portion. The original scion portion can be cut back and left to callus so as to leave shoots and foliage from only the new scion portion. 5 [101]. The embodiments exemplified in the drawings (and optionally one or more other embodiments) overcome the extended nursery time for propagating some plant species (such as Citrus species) by grafting. The extended nursery time may arise from the need to firstly graft an interstock stem to a rootstock tmnk, wait for a functional union to form and for the interstock stem to grow sufficiently so as to be capable of supporting a scion. 0 Once the interstock stem has grown sufficiently, the scion is then grafted thereonto and the resultant hybrid tree allowed to grow. [102]. The present invention has been described in some regards with reference to specific scion/interstock/rootstock combinations. It is contemplated however that the present methods may be extended to other combinations, and particularly other combinations

5 which present the same or similar problems as detailed in the Background section herein.

[103]. It will be appreciated that in the foregoing description, various features of aspects of the invention are sometimes grouped together in a single embodiment, figure, or description thereof for the purpose of streamlining the disclosure and aiding in the0 understanding of one or more of the various inventive aspects. This method of disclosure, however, is not to be interpreted as reflecting an intention that the claimed invention requires more features than are expressly recited in each claim. Rather, as the following claims reflect, inventive aspects may lie in less than all features of a single foregoing disclosed embodiment. 5

[104]. Furthermore, while some embodiments described herein include some but not other features included in other embodiments, combinations of features of different embodiments are intended to fall within the scope of the invention, and form different embodiments, as would be understood by those in the art. For example, in the following0 claims, any of the claimed embodiments can be used in any combination.

[105]. In the foregoing description, numerous specific details are set forth. However, it is understood that some embodiments of the invention may be practiced without these specific details. In other instances, well-known methods, stmctures and techniques have5 not been detailed in order not to obscure an understanding of the invention.

[106]. Thus, while there has been described what are believed to be the preferred embodiments of the invention, those skilled in the art will recognize that other and further modifications may be made thereto without departing from the spirit of the invention, and0 it is intended to claim all such changes and modifications as fall within the scope of the invention. Steps may be added or deleted from a method, and functionally equivalent operations and intermediates may be interchanged.

[107]. Those skilled in the art will appreciate that the invention described herein is susceptible to further variations and modifications other than those specifically described.

It is understood that the invention comprises all such variations and modifications which fall within the spirit and scope of the present invention.

[108]. While the invention has been disclosed in connection with the preferred embodiments shown and described in detail, various modifications and improvements thereon will become readily apparent to those skilled in the art.

[109]. Accordingly, the spirit and scope of the present invention is not to be limited by the foregoing exemplary embodiments, but is to be understood in the broadest sense allowable by law.

Claims (50)

CLAIMS:

1. A method for producing a grafted plant, the method comprising the steps of: providing a plant rootstock portion, a plant scion portion comprising bud tissue, and a

5 plant interstock portion; disposing the plant interstock portion between the plant rootstock portion and the plant scion portion such that the plant interstock portion is contacted with the plant rootstock portion and the plant interstock portion; wherein the plant rootstock, interstock and scion portions are prepared, and the steps of0 disposing and contacting are performed such that a functional union is formed between (i) the plant rootstock portion and the plant interstock portion and (ii) the plant interstock portion and the plant scion portion.

2. The method of claim 1 , wherein the plant scion portion is obtained from a plant of the5 genus Citrus.

3. The method of claim 2, wherein the plant of the genus Citrus is Citrus reticulata.

4. The method of any one of claims 1 to 3, wherein the plant rootstock portion is incapable0 of forming sufficient functional union with the plant scion portion such that the grafted plant is viable for at least 1, 2, 3, 4, 5, 6, 7, 8, 9 or 10 years.

5. The method of any one of claims 1 to 4, wherein the plant rootstock portion is incapable of forming sufficient functional union with a scion obtained from Citrus reticulata such that the5 grafted plant is viable for at least 1, 2, 3, 4, 5, 6, 7, 8, 9 or 10 years.

6. The method of any one of claims 1 to 5, wherein the plant rootstock portion is obtained from a plant of the genus Poncirus. 0

7. The method of any one of claims 1 to 6, wherein the plant of the genus Poncirus is Poncirus trifoliata.

8. The method of any one of claims 1 to 7, wherein the plant interstock portion isobtained from a Citrus x sinensis plant .

5 9. The method of any one of claims 1 to 8, wherein a portion of the plant rootstock portion has been removed to expose a region configured to contact and form a functional union with a surface of the plant interstock portion and the plant scion portion.

10. The method of claim 9, comprising mobilising a region of bark of the plant rootstock0 portion so as to accommodate the plant interstock portion and/or the plant scion portion such that the mobilised region of bark overlies a region of the plant interstock portion and/or a region of the plant scion portion.

11. The method of any one of claims 1 to 10, wherein the plant interstock portion comprises5 or is devoid of bud tissue.

12. The method of any one of claims 1 to 11, wherein the rootstock is devoid of a region of bark which has been mobilized and/or the method is devoid of the step of mobilising a region of bark of the plant rootstock portion. 0

13. The method of any one of claims 1 to 12, comprising removing a portion of the bark of the plant rootstock portion so as to provide a contact surface configured to contact and form a functional union with the plant interstock portion and/or the plant scion portion. 5

14. The method of claim 13, wherein the contact surface of the plant rootstock portion is configured to contact the plant interstock portion and/or the plant scion portion is elongate and a surface of the plant interstock portion and/or the plant scion portion is configured to contact the contact surface is/are elongate. 0

15. The method of any one of claims 1 to 14, wherein the plant interstock portion comprises (i) a first contact surface configured to contact and form a functional union with a contact surface of the plant rootstock portion, and (ii) a second contact surface that configured to contact and form a functional union with a contact surface of the plant scion portion.

16. The method of claim 15, wherein the first contact surface is adjacent to the second

5 contact surface.

17. The method of any one of claims 1 to 10, wherein the plant interstock portion comprises bud tissue. 0

18. The method of claim 17 when appended to claim 15, wherein the bud tissue extends from a position below the second contact surface.

19 The method of claim 17 or claim 18, comprising the steps of causing or allowing a bud shoot to form from the bud tissue of the plant interstock portion to burst and then removing the5 bud shoot.

20. The method of any one of claims 1 to 19, comprising the step of applying binding means to maintain contact between (i) the plant rootstock portion and the plant interstock portion and (ii) the plant interstock portion and the plant scion portion. 0

21. A plant interstock portion for producing a grafted plant, the plant interstock portion comprising an inward facing surface configured to contact and form a functional union with a plant rootstock portion, a first outwardly directed contact surface configured to contact and form a functional union with a contact surface of the plant scion portion, and (ii) a second outwardly5 directed surface that is incapable of contacting and forming a functional union with a contact surface of the plant scion portion.

22. The plant interstock portion of claim 21 that is elongate. 0

23. The plant interstock portion of claim 21 or claim 22, wherein the first outwardly directed contact surface is positioned above or below the second outwardly directed surface.

24. The plant interstock portion of any one of claims 21 to 23, comprising bud tissue.

25. The plant interstock portion of claim 24, wherein the bud tissue extends from the second

5 outwardly directed surface.

26. A grafted plant produced from a plant rootstock portion, a plant interstock portion and a plant scion portion, wherein a functional union has formed or in the process of forming between (i) the plant rootstock portion and the plant interstock portion and (ii) the plant interstock portion0 and the plant scion portion.

27. The grafted plant of claim 26, wherein the plant scion portion is obtained from a plant of the genus Citrus. 5

28. The grafted plant of claim 27, wherein the plant of the genus Citrus is Citrus reticulata.

29. The grafted plant of any one of claims 26 to 28, wherein the plant rootstock portion is incapable of forming a functional union with the plant scion portion. 0

30. The grafted plant of any one of claims 26 to 29, wherein the plant rootstock portion is incapable of forming a function union with a scion obtained from Citrus reticulata

31. The grafted plant of any one of claims 1 to 5, wherein the plant rootstock portion is obtained from a plant of the genus Poncirus. 5

32. The grafted plant of any one of claims 26 to 31 , wherein the plant of the genus Poncirus is Poncirus trifoliata.

33. The grafted plant of any one of claims 26 to 32, wherein the plant interstock portion is a0 chip configured to be predominantly or completely overlaid by the plant scion portion.

34. The grafted plant of any one of claims 26 to 33, wherein a portion of the plant rootstock portion has been removed to provide a region which contacts and forms a functional union with a surface of the plant interstock portion.

5 35. The grafted plant of claim 34, comprising a previously mobilised a region of bark of the plant rootstock portion which accommodates the plant interstock portion and/or the plant scion portion such that the previously mobilised region of bark overlies a region of the plant interstock portion and/or a region of the plant scion portion. 0

36. The grafted plant of any one of claims 26 to 35, wherein the plant interstock portion is devoid of bud tissue.

37. The grafted plant of any one of claims 26 to 36, wherein the rootstock is devoid of a region of bark which has been previously mobilised. 5

38. The grafted plant of any one of claims 26 to 37, wherein the plant rootstock portion has a portion of its bark removed so as to provide a contact surface which contacts and forms a functional union with the plant interstock portion. 0

39. The grafted plant of claim 38, wherein the contact surface configured to contact the plant interstock portion is elongate and a surface of the plant interstock portion which contacts the contact surface is elongate.

40. The grafted plant of any one of claims 26 to 39, wherein the plant interstock portion5 comprises (i) a first outwardly directed contact surface which contacts and forms a functional union with a contact surface of the plant scion portion, and (ii) a second outwardly directed surface that is incapable of contacting and forming a functional union with a contact surface of the plant scion portion. 0

41. The grafted plant of claim 40, wherein the first outwardly directed contact surface is positioned above or below the second outwardly directed surface.

42. The grafted plant of any one of claims 26 to 41, wherein the plant interstock portion comprises bud tissue and/or a bud shoot.

5 43. The grafted plant of claim 42 when appended to claim 40, wherein the bud tissue and/or the bud shoot extends from the second outwardly directed surface.

44. The grafted plant of claim 17 or claim 18, wherein a bud shoot has been removed. 0

45. The grafted plant of any one of claims 42 to 44, wherein the bud tissue and/or stump of removed bud shoot is callused.

46. The grafted plant of any one of claims 26 to 45, comprising binding means which maintains contact between (i) the plant rootstock portion and the plant interstock portion and (ii)5 the plant interstock portion and the plant scion portion.

47. The grafted plant of any one of claims 26 to 46, wherein the plant interstock portion is not partially or fully obscured by a bark portion of the plant rootstock portion. 0

48. The grafted plant of any one of claims 26 to 47, wherein the functional unions formed between (i) the plant rootstock portion and the plant interstock portion and (ii) the plant interstock portion and the plant scion portion are both visible.

49. The combination of the plant interstock portion of any one of claims 21 to 25 with a plant5 rootstock portion and/or a plant scion portion.

50. The combination of the plant interstock portion of any one of claims 21 to 25 with a plant rootstock portion and a plant scion portion. 0