by Jovita Turan, 28 June, 2020
INTRODUCTION
Rose is a woody perennial flowering plant of the genus Rosa and it belongs to the family Rosaceae. Plats are usually prickly erect shrubs, climbing or trailing with pinnate leaves. Roses have showy flowers with five petals in the wild state but often double or partly double petals under cultivation. Flowers vary in size and shape and are usually large, in colors ranging from white through yellows and reds.
Roses predate mankind on earth by about 10 million years. These early species were hardy and vigorous varieties that had only 4 to 8 petals, but they were the parents responsible for the serendipitous development of the rose as we have come to know it today. Almost 300 varieties, commonly referred to as Species, have been identified in this category and are responsible for the evolution of the Rose as we know it today. Throughout the history of civilization, the rose has played important roles in almost every walk of life. From poetry to music, from festivities to wars, the rose has been an integral part of society.
Rose is one of the most important commercial crops. It is generally propagated by vegetative methods like cutting, layering, budding, and grafting. Seeds are used for propagation of species, new cultivars, and the production of rootstocks. The purpose of this article is to analyze and describe different techniques of rose propagation.
PROPAGATION BY SEEDS
Growing roses from seed certainly not the fastest method of propagating roses, however, it is the most rewarding way and is used for new cultivars development. Rose propagation from seeds can be an interesting experiment, even though this propagation method does not produce exact duplicates of the parent plant.
The time to start rose propagation by seeds is after the hard frost in the fall. The first step in rose propagation from seed is to gather the rose hips. Roses are bi-sexual, having both the male (stamen) and female (ovary) organs that pollinate themselves and set hips full of seeds. Generally, it takes about four months for rose hips to mature enough to produce viable seeds that would be suitable for rose propagation.
Depending on the type of rose plant, rose hips will generally turn orange, yellow, red, or brown when they are mature but others stay green even when they are ripe. Only rose hips that remain on the plant are useful for rose propagation. They may be stored in the refrigerator for several weeks in case of delayed further steps.
During the next step, each rose hip has to be cut in half and seeds have to be removed. Rose hips may contain from one to forty seeds per hip. Seeds should be rinsed under running water to remove the pulp. Alternately, the seeds can be rinsed in a solution of purified water (any bottled water will do) with 5% bleach. This would be about two teaspoons of bleach per cup of water. Firstly, the rose seeds have to be rinsed with plain bottled water in a strainer, then soaked in straight 3% peroxide for 24 hours and rinsed and strained again after this process. A sharp blade in this step can damage the seeds.
Removed and cleaned seeds have to be placed in a plastic bag along with some damp peat moss and be kept in a warm room for about four weeks. If some mold appears within the bag it will help break down the very hard shell of the seeds so they can more easily germinate. After the four weeks warm stratification, the bag of seeds has to be moved into the refrigerator for another six – ten weeks before planting of cold stratification.
The next step for rose propagation with seeds is to plant all of the seeds in a flat about a 1.30 cm deep and a 2.6 cm apart, using either sand or vermiculite as a planting medium as well as a very light mixture of 50% sterile potting soil and 50% vermiculite.
The planting medium has to be moist but not soggy while the seeds germinate, in a fairly cool area where the temperature is about 12 to 15 degrees Celsius. While the seeds are sprouting spray may be needed with a fungicide if any mold develops on the seedlings or the planting medium and they have to be placed in direct sunlight.
When the seedlings develop their first true leaves, they can be potted up. Once potted, seedlings require a weak dose of fertilizer with every other watering. They have to be kept in a warm area where the temperature is at least 20 degrees and give them plenty of direct light for sixteen hours each day. It takes at least three years for a new rose seedling to reach maturity by developing into a big bush. And, it can take up to five years to completely evaluate them.
PROPAGATION BY CUTTINGS
Some varieties of rose also grow well from cuttings prepared from ripened growth in September and October and rooted outdoors in a sheltered border. This is a method especially suitable for the increase of rambler roses, shrub roses, and the various species. It can sometimes be used successfully with other types, including some of the vigorous hybrid tea and floribunda roses. Rooting cuttings is a relatively simple matter. It is the way most old roses were handed down from one family member or friend to another, and the way many old rose collectors prefer growing them today.
Roses may be rooted at any time of the year. However, freezing weather is not good and summer heat can certainly be a challenge for cuttings to root before dehydrating. The success is much more likely in the milder weather of late spring and early fall.
The easiest part of the rose to root is the tip of stems that have recently bloomed. Ideally, these tips have withered flowers, or hips, beginning to form. The flower heads or hips should be removed down to the first set of healthy leaves. Cuttings should be 15 to 20 cm long and be cut from the parent plant with a sharp knife or pruning shears at about a 45 degree angle and may remain 3-4 growth buds along the stem. It is important that the cuttings not be allowed to dry out or be exposed to extreme heat or cold, at least until they are stuck into the rooting medium. Experienced old rose collectors often carry Styrofoam ice chests, plastic bags, a small amount of water, and ice if they are likely to be in very hot conditions before getting the cuttings to the rooting area. Cuttings may be stored for several days in this manner.
Before planting the cuttings, to maximize the chances of roots forming some actions can help. For instance, the foliage removal (except thorns), wounding of cuttings as this helps to expose more of the cambium layer – this is the area where the roots will be produced from and it is light green color. The use of rooting hormones has been shown to increase the percentage of cuttings to root and the number of roots per cutting, but it is not necessary for success because roses naturally produce auxins at the cut that stimulate root production. Rooting hormones are commercially available in powder form and are popular with some rose growers. Others also like to use 2,5 cm sections of cut branches from willows, cut both horizontally and laterally, to soak in a pan of water that has been brought to a rolling boil (rainwater is ideal). Research at the Ohio State University has shown that willows (apparently any species of Salix) contain substances that can induce rooting and prevent ‘damping off’ or canker in other plants.
Selecting the site for sticking the cuttings is very important. Roses prefer a sunny location, but for rooting purposes, it is usually best that they are shielded from the hot afternoon sun. Bright light, but not direct sunlight, is ideal. It is also good if a location can be chosen where the soil is sandy and well-drained, and where drip from the roof helps to keep the area moist. The sand or sandy soil should be amended with l/4 to l/3 peat moss, composted pine bark, or similar material. Though, 50/50% blend of potting soil and perlite is mostly recommended rooting medium. The cuttings remain moist while at the same time the soil drains well as the perlite provides excellent aeration to the roots.
Foliage on the lower half of the cuttings should be removed, but allowed to remain on the upper part. After dipping into powdered rooting hormone, soaking in willow water, or with no hormone treatment at all, the cuttings are ready to stick into the media. If a powdered hormone is used, some of the material from the container has to be removed remove, each cutting has to be rolled or dipped into the material and taped lightly to remove any loose powder. Wooden pencil or dibble is used to make a hole for each individual cutting. The cuttings should be stuck half the length of the cutting into the media to prevent damaging the cutting as it is stuck or unnecessarily removing the rooting hormone. The cuttings should be placed 15 or 20 cm apart in rows with the soil carefully firmed around each cutting, labeled with a permanent marker stating the variety, if known, or the site where collected, including the date the cuttings were stuck.
It is especially important early in the rooting period of the cuttings that they not be allowed to dry out but not get too wet and rot. Plastic bags can be used over the top of pots to maintain high humidity. Moreover, extreme cold can cause damage that could have been prevented by covering cuttings for a few hours or days.
During the first month or two after being stuck, the cuttings begin to develop what is called ‘callus tissue’. It is a swelling on the cutting tip and other areas where roots are to develop. As winter begins to turn to spring, the cuttings will sprout roots and new growth. This is a critical time for the new plants and it is important that they not be allowed to dry out. Although the plants are usually well rooted by late April or May, it is best to leave them in place until the next fall or winter. New roots are very fragile and break easily and plats are extremely vulnerable to stress the first summer and are best left to develop a good root system.
Once the cuttings have formed roots, they can be transplanted carefully into larger pots or the garden, again keeping them well watered. They will be small, but most varieties grow quickly and produce a fair quantity of flowers by next spring. To protect them from wind damage, it is a good idea to prune back any tall shoots and thin the plants sparingly, if possible, at the time they are being transplanted. During the naturally dormant period in late winter, the plants may be dug either with a ball of soil or bare root. For best results, plant in locations receiving at least a half-day of the sun in well-prepared soil. A regular fertilizer program may be started by mid-spring.
PROPAGATION BY GRAFTING
Grafting is chiefly employed by trade rose growers for the rapid increase of new varieties as roses are propagated by taking a cutting or a bud from a selected variety and attached to a selected rootstock. The advantage, in this case, is that the work can be carried out in a warm greenhouse in January or February. Then buds obtained from the resultant rose plants can be used for budding in July; in other words, two generations can be obtained in one season.
There are several methods of grafting, but the simplest is splicing, which consists of matching the tapered edge of the scion with precision to the cut edges of the bark of the stock. The rootstock plants for grafting are usually produced from cuttings. Firstly, the rootstocks should be rooted from cuttings then the budding or grafting operations take a place. Some growers graft and root the rootstocks at the same time; this technique is called stenting.
For a rootstock either softwood (at a stage where leaves are well developed) or semi-hardwood material needs to be selected of 6-8 mm diameter from actively growing plants. It is advisable to remove all buds from the stock to overcome the problem of excessive suckering. The length of stock can be varied between 50 and 400 mm. A 50 mm length will give acceptable results but stocks that are 100 mm long are easier to work with. Rockwool is an excellent rooting medium, however, sand/peat mixes and peat/perlite mixes have also been used with success. For a scion, glasshouse-grown softwood/semi-hardwood cuttings with one or two well-developed leaves are the most suitable. Many growers also favor material taken from stems that carry well-aged flower buds and in which the eyes or buds are nicely plump but still dormant.
Firstly, a thin slip of bark is removed from the lower part of the scion to expose the wood and form a tongue. Each scion needs no more than two joints, one on the portion shaved to form the tongue to attach to the stock, and one above to break into growth. Then, the stock needs to be headed back, leaving just sufficient stem above the soil to take the tongue of the scion, very little more than 2,5 cm is required for this. A shallow strip is shaved from the side of the briar stock. This must exactly correspond in length and breadth with the tongue cut on the scion so that the two will fit perfectly together with no gaps, cavities, or overlapping edges. Union of the two is only possible when the two barks fit exactly. The grafting should ensure that a large cambium layer interface occurs for a strong union and effective vascular connection. The graft union can be held together by tying with non-adhesive PVC tape but if short stocks/scions are used, pinning or clamping with pegs may be more convenient after bounding firmly, the grafting can be sealed with wax.
Alternatively, the scion can be cut with a taper and a vertical incision made in the bark at the top of the stock, which is first beheaded. The bark is then prized open, as in budding, and the tapered part of the scion is slipped down under the bark so that exposed the tissue lies closely against tissue. Then all is bound with raffia.
The pots with grafted plants are plunged in sand or peat in a close frame in a warm greenhouse. The soil in the pots must not be allowed to dry out, and the atmosphere needs to be kept humid by the use of the syringe when needed. As the eyes break into growth ventilate the frames increasingly to acclimatize the plants to cooler conditions.
PROPAGATION BY AIR-LAYERING
Another method for propagating roses is the air layering method. About 4000 years ago the Chinese people used it to duplicate plants that were difficult to root by cuttings. It is one of the easiest methods of propagating a rose, and when done well and at the right time, you can get an absolute 100% success rate. Some roses may take a little longer to root, but most will only take between 3 and 8 weeks to root. There is no trauma to the mother plant; in fact, it will promote growth as if you pruned that branch. Healthy new shoots will sprout below the air-layer. Another benefit of air layering is that new rosebush may continue blooming, even as it develops its new roots. The perfect time to air layer a rose in during the spring, just after its first bloom, because this is the time that they are actively growing.
To start, a stem has to be chosen from a healthy rose plant that has already borne a flower, it should be pencil size, still be green, without woody bark, and have swelling buds with no signs of disease or insect damage. This is the perfect indication that the stem is mature enough to root. To speed up the rooting process and encourage vigorous growth, it is a good idea to take additional care of the plant.
During the next step, the leaf-sets and thorns have to be removed. Layering has to be done in the area just below the first five leaf-sets. The first cut should be 0.6cm below a leaf node in the stripped area, and the second 2.5 cm below the first and they have to be only as deep as the bark, which has to be gently peeled off.
Then, the soft tissues need to be scraped off gently and the rooting hormone has to be applied with a small brush. In the end, a plastic sheet has to be wrapped around the stem, taping the adjoining edges to form a tube. The bottom end of the tube needs to be tied with a twist tie and the peat moss needs to be placed around the cut. Twisting the tie too tight will strangle the stem and prevent it from growing, but it has to be tight enough to ensure that any excess moisture can still run down the stem.
The parent plant has to be kept well-watered. When white roots are visible, the plastic should be removed as usually it happens in three to six weeks. Cut should be done through the cane below the new root ball with sharp, clean bypass pruners. Then, the newly rooted cane can be cut down to no more than 25 cm tall, removing all leaves and side shoots so the fledgling roots have less growth to support. The cutting should be planted that root ball remains under the soil in a clean nursery pot filled with moist potting mix. The potted plant has to be moved to an area in bright, indirect sunlight. The soil has to be consistently moist until late fall when the plant prepares for dormancy. New roses can be planted in full sun in late winter to early spring before it begins to leaf out.
MICROPROPAGATION
New cultivars development utilizes seeds while cuttings and budding are commercial methods of propagation. However, these methods of propagation are not sufficient to produce a large number of good quality and high yielding plants to fulfill growing demand because these methods have slow multiplication rate, attack of different insect pests, diseases and unfavorable weather conditions. To produce a higher yield of better quality, healthy and disease-free plants of roses round the year, micropropagation is a viable technique.
Significant features of the in vitro propagation procedure are its enormous multiplicative capacity in a relatively short period and its ability to generate propagules around the year. Using this technology, up to 400,000 plants could be cloned, from a single rose on an annual basis.
Micropropagation methods of regeneration are different from conventional propagation methods in several ways. In the micropropagation way, the artificial growth medium is used instead of soil, light, temperature, and humidity are adjusted according to plant requirements and any plant part can be used. Healthy and disease-free plants are produced without any season effect and many plants can be produced from a single plant part, haploid plants can be produced, plant breeding cycle can be shortened and can be used to produce mutations in plants. A successful micropropagation protocol proceeds through a series of stages, each with a specific set of requirements. These are the initiation of aseptic cultures, shoot multiplication, rooting of micro shoots, and hardening and field transfer of tissue culture raised plants.
There are different direct and indirect techniques of micropropagation of roses. In direct techniques, shoots are developed from the explant tissue without callus formation e.g. meristem culture. In this technique small, (0.2-0.5 mm) pieces of meristem are used as explant. This technique is used for virus eradication because meristem has faster cell division than virus multiplication. In seed culture, seeds are cultured on nutrient medium to develop shoots and roots. In indirect techniques, first callus is developed from the explant and from callus, shoots and roots are developed e.g. leaf culture. In this technique, small leaf segments having mid rib are used to culture and produce callus, which further develops into shoots and roots. In anther culture, anthers (male part of a flower) are used as explant to produce haploid plants used in the breeding program. For root culture, root segments are used as explant. In cell culture, only cell can be used as explant after separating from the tissue. Ovary and flower petals can also be used to develop in vitro plants.
To sum up, the main rose propagation techniques are by seeds, cuttings, grafting, layering, and micropropagation. Propagation by seeds is the most slowly one but by this method, new and different cultivars can be developed. Cuttings, grafting or budding are commercial methods of propagation, while layering can be an alternative and one of the easiest vegetative propagation method that can provide 100 % success. And finally, micropropagated plants are a healthier, disease-free, and most important use of this method can easily produce a higher yield of better quality more oil contents, rapid growth rate, and aesthetic value.
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