Grafting, a fundamental method of asexual or vegetative propagation, involves joining a scion (a detached shoot or bud) with a growing plant (stock or rootstock) to facilitate their union. This process relies on plant cell division to create callus tissue, which is a normal healing response in plants. The formation of callus tissue is crucial for establishing a successful graft union, and promoting rapid callusing is a key parameter for effective grafting.
Several factors influence callus formation, including temperature, light, pressure, moisture, and chemical growth regulators. Among these, temperature plays a particularly significant role, with optimal growth occurring within the 5° to 32° C range. Accelerating callus growth by increasing temperatures above ambient levels is known as "hot-callusing."
Challenges in Traditional Hot-Callusing
While simply placing a grafted plant in a warm greenhouse can accelerate callus formation at the union, this method has a significant drawback: it promotes growth not only at the graft union but also from the scion buds and roots. This can be problematic because the scion buds and leaves require moisture and nutrient translocation, which places demands on the graft union. If the callus bridge between the rootstock and scion is inadequately formed before significant growth occurs, the scion buds and leaves can desiccate.
To address this, nurserymen have developed specialized "sweat" boxes or frames within greenhouses to provide controlled increases in temperature and humidity. These structures are typically heated by water, steam pipes, or electric cables. Other methods have involved placing grafted trees in outdoor hot beds or barrels filled with heat-retaining media like peat moss, often heated with cables. Additionally, grafting tents have been used outdoors, creating miniature greenhouses with solar energy as the heat source. However, these approaches often suffer from high costs, labor-intensive construction, and difficulty in achieving precise temperature control.
Another technique involves placing a heating cable in moist sawdust, covering it with more sawdust, and positioning the graft union on top. This method, however, has the disadvantage of callusing the graft union primarily on one side.
The Inventive Hot-Callusing Apparatus and Method
The invention described herein provides a novel solution to these challenges by directing heat exclusively to the graft union area. This approach accelerates callusing of both the stock and scion by promoting rapid callus formation while leaving other plant parts, such as buds and roots, unheated. The primary advantage of this method is the localized application of heat, which speeds up the callusing process without stimulating premature growth in other parts of the plant. Consequently, the demand for moisture and nutrient translocation to the scion does not arise until the callus bridge between the scion and rootstock is fully formed.
Apparatus Design and Functionality
The apparatus consists of a hollow cylinder (1) equipped with a series of laterally extending openings (2). These openings are designed to sufficiently enclose the graft union area (6) of the stock and scion, thereby confining heat to this specific region and minimizing its escape. Heating means (7), such as heating cables, are placed within the cylinder to warm the air. Temperature regulation is managed by a thermostatic sensor (9).
The cylinder can be constructed from various materials, including plastic or metal, and the openings (2) are sized to accommodate the graft union. The slot width is made slightly larger than the plant's diameter to allow for easy insertion of the joined stock and scion, while remaining narrow enough to minimize heated air loss. The length of the opening is sufficient to at least partially surround the graft union area, ensuring adequate heat delivery for effective callusing.
In one embodiment (FIG. 2), two strands of heating cable (7) are separated by a material (8) within the cylinder. The thermostatic sensor (9) is positioned near the graft union to regulate the heating elements. This sensor can be located in one of the openings (2) or across several openings.
An alternative embodiment (FIG. 3) features a smaller internal hollow cylinder (10) filled with water. The heating cables (7) are attached to opposite sides of this internal pipe, preventing them from crossing and short-circuiting. The cables heat both the air within the outer cylinder (1) and the water in the inner cylinder (8). The heated water acts as a buffer, helping to stabilize the air temperature within the outer cylinder and minimize temperature fluctuations. This embodiment also incorporates insulating material (11) to cover the openings (2) and enclosed graft unions, further reducing warm air escape and enhancing heat distribution around the graft union area.
The Hot-Callusing Method
The hot-callusing method involves mechanically joining the stocks and scions using conventional techniques, such as wrapping with grafting strips. The prepared graft union is then placed into an opening (2) of the cylinder (1), ensuring the graft union area (6) is substantially encompassed. Air within the cylinder is heated, typically to a temperature between 21° and 27° C., which promotes rapid callusing. This controlled heating is maintained until a sufficient callus bridge has formed between the rootstock and scion. The duration required for callusing can vary depending on the plant species and specific conditions.
In the embodiment utilizing the internal water cylinder (FIG. 3), heating cables warm the water, which subsequently heats the air in the outer cylinder. Once the heating cable is thermostatically shut off, the warmed water continues to provide heat to the air within the cylinder, maintaining a stable temperature.
Applications and Benefits
This hot-callusing method and apparatus are applicable to a wide range of plants where accelerated callus tissue formation through heat is beneficial. It is particularly useful for grafting fruit trees, such as apple, pear, and prune, as well as nut trees like filbert and walnut.
A significant advantage is the ability to perform grafting outdoors, even during winter months, without requiring elaborate protective structures. The apparatus can be placed directly on the ground, needing only a heat source for the heating elements. This allows for year-round labor utilization, as grafting can be conducted during the dormant season when buds are not actively growing.
Trees can be bench grafted in the fall using this invention. At this time, the scion buds have not yet completed their rest period and have not begun growth. Following hot-callusing in the apparatus, the trees can be transferred to cold storage to fulfill the bud rest requirement, preparing them for nursery planting in the spring. For trees bench grafted in late winter or spring, hot-callusing can be performed just before planting. This timing ensures that by the end of the callusing period, outdoor weather conditions are suitable for planting. In regions with mild winters, trees may be planted directly into the nursery immediately after hot-callusing.
The apparatus allows for continuous operation, as one group of hot-callused trees is removed and replaced by a second group.
Experimental Results
An experiment conducted with filbert trees demonstrated the effectiveness of the method. Thirty-nine filbert tree grafts were placed outdoors in the FIG. 3 embodiment, with ambient air temperatures ranging from 10° to 13° C. The air within cylinder 1 was maintained at 27° C., and the trees remained in the apparatus for 28 days. Following hot-callusing, these trees were planted directly into the nursery. Another group of 15 trees underwent the same hot-callusing process and planting procedure, with ambient temperatures between 10° and 13° C. All of these trees (100 percent) survived planting. In parallel, a control group of 15 trees was grafted under identical conditions but without the use of the specialized hot-callusing apparatus, providing a comparative benchmark for survival rates.
A demonstration of grafting apple trees
Claims
- An apparatus for hot-callusing graft unions of plants, comprising:
- a hollow cylinder having a plurality of laterally extending openings of sufficient size to at least partially enclose the graft unions to be callused and retard the escape of air through said openings when the graft unions are in place, and confine heat to the graft unions; and
- means for heating the graft unions within said cylinder.
- The apparatus of claim 1, wherein the openings are sized to substantially surround the graft union area.
- The apparatus of claim 1, wherein the means for heating comprises heating cables.
- The apparatus of claim 3, further comprising a thermostatic sensor for regulating the heating means.
- The apparatus of claim 1, further comprising an internal cylinder filled with water, wherein the heating means heats the water, which in turn heats the air in the outer cylinder.
- A method for hot-callusing graft unions of plants, comprising:
- mechanically joining stocks and scions;
- placing the joined stocks and scions in a device comprising a hollow cylinder having openings of sufficient size to at least partially enclose the graft unions to be callused and retard the escape of air through said openings when the graft unions are in place, and confine heat to the graft unions; and
- heating air in said cylinder until the graft unions are callused.
- The method of claim 6, wherein the heating is performed at a temperature between 21° and 27° C.
- The method of claim 6, wherein the device further comprises an internal cylinder filled with water, and the heating means heats the water, which in turn heats the air in the outer cylinder.