A step by step description of the methods of propagating olive trees.
Olive tree propagation is an important topic. There is not enough time to express all the principles, but I will try to give you a quick, simple overview. Plant propagation is the multiplication of plants by both sexual and asexual reproduction. The topics I will talk about are sexual propagation, even though it is not used a lot for olives, as well as micropropagation, a new technique for the future. At the moment, vegetative propagation is used.
Some general principles of sexual propagation: the basis is the seed. A seed has three essential parts. The first is the embryo from which the new plant will develop. There is the food storage material which gives necessary sustenance to the embryo, and there is the seed covering which protects the embryo.
The flower is an important key for fertilisation: the calyx, sepals, corolla, stamens, stigma, pistil and ovule. The final product is the fruit from the ovule, with the seeds. The integuments will form the seed coats. The nucelles will be the peristyle, and the two polar nucleus will form the endosperm. The egg nucleus will mix with one sperm nucleus to make the embryo, a new plant.
This is the process: there is pollination, fertilisation, flowering, fruiting and seed. Seed formation is preceded by meiosis, typical cell division in sexual propagation, from which are formed the male sperm cells and the female eggs. They combine together to make the ovule. The zygote develops into the embryo.
The structure of the olive seed: the epicarp, the mesocarp and the endocarp. The epicarp is the external part, the fruit. The flesh is the mesocarp, itself. The endocarp is not the seed, but the hard part you see when you take away the flesh. In the seed coat we have the endosperm, the cotyledons, the hypocotyl and the radicle. These are the starting point of the new plant.
Why do we propagate olives sexually? First of all, to obtain rootstock material, for breeding to obtain new cultivars, for breeding new rootstock genotypes, and to obtain deeper and stronger root systems for at least the first stage. It has been proven that root systems grown from seeds are stronger and more consistent than root systems derived from rooting.
What are the advantages and disadvantages of sexual propagation? If plants have viruses, seeds can produce virus-free plants. No skills are required, even though there are some mechanical and chemical encouragements that can be done to promote the germination of the hard seeds. Also, this material is inexpensive and they give a stronger root system. The disadvantages are low germination sometimes, 20% to 60%, or even less than 10%, which is not viable commercially. And plants have variability. With vegetative propagation, from the same mother trees, we get homogenous plants. Also, plants from seeds have a longer juvenile stage.
I will speak quickly of micropropagation, tissue culture, as is it not something you can do yourself for your orchard. Micropropagation is the culture of plant material, maybe buds or node cuttings, even embryos. This requires a completely sterile environment. Usually micropropagation is done in glass or plastic vessels which are incubated in controlled environments. It is important to control climatic temperature, humidity and light.
A medium with substances that all plants require, such as carbohydrates, mineral salts, vitamins and amino acids, is used. Crucial to this process are growth regulators, particularly cytokinins, auxins and gibberellins. They promote cell extension, root formation, leaf expansion and organ development.
Micropropagation includes five stages: establishment, multiplication, rooting, transplanting and acclimatisation. Establishment, first of all, is the collection of the parts we are going to use for propagating material, maybe microcuttings with one or more buds. Then there is the sterilisation of this material, because we don't want to infect the medium, and we want plants which are completely free from pests and diseases. It is crucial that the plant material is from a known genetic source of good quality. Collection of this material should be done in spring because that is the best time when vegetative activity is high. A growth chamber set at 20 to 24 degrees Celsius is used, with 2000 to 4000 lux light intensity, and a lighting period of 16 hours or so.
Cytokinins are important because they stimulate the bud and we get more branching, more material to propagate. One plant can be used to produce up to ten thousand plants. But this doesn't work for olives. The olive plant has a strong apical dominance so it doesn't branch a lot. We have to wait about 50 days to get ex-plant material which is one bud, which we may use for further multiplication. This method may work well for other kinds of plants but not for olives. There are only a few times when this method is used for olives. Auxins are hormones that encourage the rooting of cuttings. It has been found that less use of cytokinins (or better still, no use of cytokinins) improves the rooting of the material. It has also been found that some bacterial infection may encourage the rooting process.
Transplanting and acclimatisation are the last two phases of micropropagation. We have to transfer the plants from vitro to vivo, in other words to a more natural situation. The plant passes from the heterotrophic stage where it has to be fed to the autotrophic stage when the plant starts producing its own food and growing roots, shoots and leaves. It is very important to know the concept that the initial humidity must be quite high, about 90% to 95% but later on it has to be slowly reduced in order to harden the plant and adapt it to the external environment. A mix of peat and sand is used.
I would say that micropropagation is an efficient multiplication technique to produce plants in reduced space and in a relatively short time. Again, it is not so for olives because the proliferation is very low, the apical dominance for olives is quite high, which is an obstacle to the branching and production of material. Also, deatin (?) which is a cytokinin is required, and it is very expensive. So it doesn't work from an economic point of view. And the rooting phase is not very efficient. However, micropropagation for olives may be used to obtain the best plants, to propagate olive plants for a collection of germplasm, and, of course, to research the physiology and nutritional value of the olive plant.
Vegetative propagation is currently the most important technique. Lots of nursery people are making a lot of money; there is a big demand for olive trees in Australia. It is a very good business. And it is not very hard. Vegetative propagation is used to produce plants which are going to be identical in germ type with the mother plants. The best method would be to obtain the mother trees by cloning, but it is still too early for that here in Australia. Everyone is saying, OK, that's the best variety, that's the one you should plant. But how can you prove that what they say is so? We need several years before saying that any variety is the right one, the best one. Even so, the beginning is quite good to understand that maybe Manzanillo or Corajollo (?)or Arvaquina are the best varieties. But it still takes several years before you can speak with certainty of the best varieties for a given environment.
This type of propagation is accomplished by a cell division process which is mitosis. What are the advantages of vegetative propagation? Uniformity of plants, same characteristics as the mother tree. If we identify a good variety, we propagate this variety, we grow it and we get good material. Rapid growth and development, more or less in 12 to 14 months we can make a lot of plants which are ready to plant in the ground. Early production and of course economic returns. When we talk about vegetative propagation, I refer to two types of propagation. One is propagation by cuttings in a medium, and the grafting and budding. It still implies the use of the vegetative part of the bud, not the seed. You use a rootstock and scion.
I will talk about propagation by cuttings. We have different types of cuttings: propagation by ovulists (?), suckers, hardwood cuttings, trenches (tranches?). It is quite old-fashioned now. These are the ones from ovulists, because these big old olive trees develop a sort of cell hyperplastic mass (?) along the trunk. You use an axe, you get the ovules (?) and put them in the ground and you get new trees from there. It is quite a long process, but quite cheap. That is how lots of old olive orchards in Italy have been propagated. Mostly by ovules. Suckers come from the bottom of trees, but we don't use them now. We now use leaf-stem cuttings.
The factors that affect success of propagation include external and internal factors. The internal factors are genetically determined. We have varieties such as Frantoyo (?) and even Manzanillo which root very well. I am in charge of the management of a big olive nursery, and we have a very high success rate with Manzanillo and Corojollo. But Kalamata, the Greek table olive variety, has a very low rate of rooting, 5% to 20%. In other words, it is better if we graft this variety rather than propagating from cuttings.
Cuttings are taken in late summer and early spring. Early autumn when there is still plenty of sun and there is a flush of vegetative activity is the best time. Last year I started taking cuttings on the 15th of April, and I had a success rate of 89% with Manzanillo and Corojollo varieties. Spring is also a good time when vegetative activity is high.
It is important to select the right cutting material. Usually you take one-year-old shoots, the basal part and the medial part. The apical part is too soft and doesn't root very well, according to my experience in this sort of climate. It is important to discharge the juvenile shoots that grow all along the trunk. They root better than one-year-old material, but when you sell the plants they are delayed in production. If a normal cutting takes three or four years to produce, the juvenile cuttings may take twice as long to begin to produce.
External factors include the use of hormones. You need to know which hormones to use and the concentration to use. The most commonly used hormone is indolebutyric acid, which is the best in my opinion. Others include naphthaleneacetic acid and indoleacetic acid, which are good. The concentration I use is 4000 ppm, and also 2000 to 3000 ppm should be OK. It is important that the mother trees are certified, that you know the source and genotype. An efficient and effective nursery has to know the varieties. It is the most important thing. Any good nursery has to have the mother trees around so the customer can be shown and allowed to choose. To allow the customer to feel sure he is making the right choice.
It would be ideal if the mother trees were cloned, set fruit and continuously checked for mutations. Because if there is a mutation, then you don't get the material you wish you would. It is important to understand this physiological principle. It should be free of pests and diseases, with a good carbon-nitrogen ratio. The higher this relationship, the better the rooting, experiments tell us. Equilibrate fertilisation, because a lot of people apply a lot of nitrogen to push growth, because they believe they will get more shoots, more cuttings. This is wrong. The more nitrogen you add, the more unbalanced the nutrients. This relationship is not good for the success of rooting. And your management of the mother trees should be optimum.
The environments of the nursery. The first phase of propagating takes 8 to 12 weeks, with an average figure of 10 weeks. We need a glasshouse for this first phase. We need a greenhouse for the second phase, for the hardening period, and we need a shade house to make the plants grow and develop. It would be good to have standard construction, as we had to have a consistent environment for micropropagation. A modern nursery should have it, but it is not compulsory. You should have good quality water, you should have an environment to keep chemicals, fertilisers, to keep them all in proper containers, and a place to keep all the tools that are used in the nursery.
This is the glasshouse for the propagation of first phase. We need some beds, maybe (...?) or Fixit (?). Inclination is absolutely crucial because we don't want waterlogging. If the water stays there, you won't get good rooting. Two things may kill the cuttings at that stage: too much water or not enough water. It is very important to provide the water in the medium but at the same time have good drainage.
Now we need a misting system, of course. Temperature control system--why did I put automatic or manual? Automatic is the best. You switch on and it goes, but sometimes there is a problem with the power or something, and one or two days is enough to make you lose everything. So, you have to be able to control also manually. The lighting control system. Here in Western Australia in summer there are very hot days, and the greenhouse gets a lot hotter inside than outside. The floor should be concrete and sloped.
The third phase, very simple, no need to have complicated things: a shadow (shutter?) (shed?) system. If you don't have a problem with frost, if you didn't find the best time to propagate, the plants must stay outside after the hardening time of the second stage. You should have a shed or something to guarantee that nothing will happen. You have to have them in two-litre containers, which they prefer. A lot of nursery men use smaller containers which stress the plant. If you leave the plants there 12, 14, 15 months there is no room in 8mm containers, 1 litre container, for the root system to grow and develop. There is no room. It is an economic issue, of course. We need a fertigation system, individual dripper system, the methodology they use in Tuscany and (...?), again a sprinkler system, electrical and doorways.
Now I will give you some practical numbers. Rooting, first phase: You get the cuttings, one-year-old wood, liniefied (?) and not vertical. As soon as it is vertical, it is juvenile. You can see the difference by looking at the internodes. You need the ones that are inclined at 45 degrees or thereabouts.
Preparation of cuttings: 10 to 12 cm in length, 4 to 6 nodes, 2 or 3 buds without leaves. You leave the leaves in the last two nodes, and they are 2 to 4 mm. You may use an alcohol solution like I use, which is good. You may use the (...?), you may use the (...?), you may use the (...?). The concentration that I have been using is 4000 ppm, but it can be lower. The treatment must be done as soon as possible once you prepare the cuttings, no more than 24 to 40 minutes, particularly if it is a hot day.
You make perhaps 20 cuttings, tie them together and dip into the hormone solution for five seconds. Ideally, within twenty minutes, the cuttings should go into perlite medium in the first phase hothouse, with a humidity of about 95%. It is crucial. If you don't keep this high humidity during the first week, they will lose their leaves and die. Bottom heating should be 18 to 24 degrees Celsius. I would advise you to use the lower temperature even if it takes longer, because it does not dry the environment excessively. It is a little bit easier to keep a higher moisture content. The leaves should stay humid in between the two cycles of misting. If it is hot outside, you need a cooling system or the environment may dry out. The 95% humidity is crucial.
The first week 12 to 15 seconds of misting every 10 to 12 minutes. Second week, 10 to 12 seconds every 12 to 15 minutes, third week, 7 to 10 seconds every 15 to 18 minutes. In other words, we are reducing the time of misting and the intervals longer.
It is very important after 25 or 30 days to check the cuttings. By then you should have some root initiation. The first transplant should be after 10 or 12 weeks, when the root system is quite long, about 3 to 5 cm long and the colour has turned from white to brownish. It is quite consistent, it is not very fragile, and this is the best time to do the first transplant. If the cuttings stay longer in the first phase in the glasshouse, you have to reduce the moisture in the air, because by now there is a root system. The higher the moisture in the air, the higher it will be in the medium, so it is very important to reduce the moisture in the air.
Second phase, after the first transplant, roots 3 to 5 cm, colour grey-brown, and they are reasonably hard, thick roots. The temperature in the glasshouse or greenhouse 20 to 24 degrees, humidity 75% to 85%. We start with 85% and reduce to 75%, because we want to reduce gradually to acclimatise these cuttings, which come from a really delicate environment, very humid, to the external conditions. I recommend the pots for the first transplant be 300 to 500 mm. The medium is perhaps 40% peat, rock pumice 40%, compost 10%, sand 10%. Be careful of the compost, because we don't want waterlogging. This can kill the trees at this stage. We don't want a lot of water in the medium. So it is probably better to have not more than 10% compost. At this stage, there is no need to put in any fertiliser. The root system is still fragile. They do not absorb water and nutrients. Don't worry about nutrients at this stage. The medium has to be well-mixed and sterilised, and the pH should be between 6.2 to 6.5.
There is no rule about how long the transplants should remain. I would say the plant has been hardened after two weeks, but to be safe, I would say to make it at least one month. One to two months is ideal, but the root system is probably OK after just two weeks. You have to water the rooted cuttings. Brief and frequent irrigation, of course, and avoid waterlogging. Remember that transplants must not be done where there is hot, windy conditions, because the cuttings are still very sensitive.
Once the plants have survived the second stage, it is very unlikely that they will die. So, after 4 to 8 weeks you do the second transplant. You look for really good, well-developed root systems. The tree is in a 500 mm pot, you pull the plant out and look at the root system. If the roots are all around, it is too late. You don't want the roots to grow all around in a root ball. You want them when they start thatching, that is the time to do the second and final transplant.
In nurseries they use a maximum of one-litre pots. My view is that this is too small. Two litres is the best one. Now, you need an automatic irrigation system. We increase the amount of compost. It was 10%, now it is 30%. The tree still may be killed by waterlogging. It is very hard to kill an olive tree, but waterlogging does the job. Again, the medium should be sterilised and well-mixed. You can put some lime into the compost as long as the pH is not higher than 6.5 or 6.6. In this case, we need some fertiliser. Slow-release fertiliser, nitrogen, phosphate and potassium. Frequent urea and calcium nitrate for fertigation.
Grafting and budding are essentially the same technique. Both involve taking a section of stem or bud and attaching it to a different plant. You want to have a plant with good productive characteristics on a good root system. You do it to make a tree more resistant to pests and diseases, more resistant to soil conditions. You want to put together suitable characteristics. Grafting terminology: the scion is the top of the grafted plant. The rootstock forms the roots of the system. Budding refers to part of a scion, usually one bud. Grafting refers to a section of stem with two or more buds. The graft union is the part where the rootstock and scion meet together. The best time for grafting is spring when the bark can easily be detached. The scion is taken from one-year-old shoots with medium vigour. They should have one or two internodes.
It is better if the rootstock is two years old, because you want a root system that is very well developed. The stress will be less. The reasons for grafting are to propagate varieties which are very hard to root, such as Kalamata variety; to propagate new varieties; to obtain plants resistant to pests and disease; and to convert mature olive trees to new varieties.
(...?) grafting, very quick because most of them are quite similar, even though they use different terminology. You cut the seedlings about 5 cm from the ground, make two cm vertical cuts on the bark. You prepare the scion, which is 3 to 5 cm length, cut it obliquely and insert the scion into the bark of the seedlings. Tie up the graft with raffia or other fibre, cover with grafting wax. Callousing takes place after 20 days or so. They should develop after 30 days. Choose the best shoots and remove the others. Other grafting methods include side grafting, clonal grafting and top-working mature plants.
Slides: Old olive trees in Italy--hard to shake. Calabrian orchard--different varieties for different regions.
I think it is important to talk about chilling requirements. Different varieties have different requirements. A variety may grow well but not set flowers because the chilling requirement has not been satisfied. The interaction of genotype with environment, acclimatisation, may give varying results. Different climatic conditions within the years is a natural way of selection. That is why there is a big number of varieties in Europe that can be used for specific environments.
Each variety has its chilling requirement in hours. The temperature should be below a certain minimum degree, a number of hours below, for example, 12 degrees Celsius. If the chilling requirement is not satisfied, the tree does not flower. The chilling requirement induces the flowering. But there needs to be a high temperature during the time of fertilising.