How to Do Hobby Breeding
Usually, amateur plant breeders work with characteristics that can be relatively easily changed - for example, flower color, fruit shape, or plant size. However, even though the experiment may seem simple, it makes it possible to produce an unusual or beautiful plant.
For successful plant breeding, it's important to understand the principles of their reproduction. This text will explain these principles and describe some of the simple techniques that can be used to produce new species or strains of plants.
Plant Selection
Plant characteristics can be changed over several generations through the process of selection. There are two types of selection - natural and artificial.
Natural selection is a process that occurs in nature, where strong and well-adapted plants survive, while weak and poorly adapted plants eventually die out. This process has been taking place since the beginning of life on Earth and still occurs in nature today.
Artificial selection is a process that people use to obtain more desirable plant species. Thousands of years ago, people learned that saving seeds from a plant variety they wanted to continue growing would increase the chance of obtaining a plant similar to its original. But our ancestors didn't know what their chances of success were, nor did they understand the processes by which traits were changed or preserved. It wasn't until the eighteenth and nineteenth centuries that people began to understand the laws of heredity and plant reproduction processes. Even today, these basic principles are not fully explained. But now we have enough knowledge to be able to select plants for breeding with considerably greater certainty of success than our primitive ancestors had.
Basics of Plant Reproduction:
Types of Reproduction
Plants reproduce in two ways – sexually and asexually.
Asexual or vegetative reproduction occurs without the fusion of germ (reproductive) cells. In garden plants, asexual reproduction occurs when a part of the plant is separated from the mother plant and develops into a complete organism, such as when strawberries produce runners that root and form new strawberry plants. Asexual reproduction can be induced artificially using leaf cuttings, stem cuttings, root cuttings, etc. Plants that originate from asexual reproduction are usually identical to the mother plant.
Sexual reproduction involves the union of male and female sex cells. Their fusion creates a seed - and eventually a new plant. Sexual reproduction is the most common type of reproduction in garden plants. Plants originating from sexual reproduction are often completely different from their parents and from each other. Thanks to the possibilities of variation, sexual plant reproduction is the method used by plant breeders in developing new strains and varieties.
Plant Flower
Figure 1 Flower Structure
Figure 2 Schematic Representation of a Flower
1.Receptacle 2.Sepal 3.Petal 4.Stamen 5.Pistil
Sexual reproduction in plants occurs in the flower. The reproductive organs of the flower are the stamen and pistil. The part of the stamen called the anther produces pollen grains, which contain male germ cells. At the base of the pistil is the ovary; it produces ovules, which contain female germ cells. When the ovules are fertilized by male germ cells, they develop into seeds within the ovary.
Petals, which significantly contribute to the beauty of flowers, serve useful functions such as aiding in pollination and protecting the sexual organs from physical damage. Sepals, which are often green, support the petals and protect the flower parts.
Flower parts vary considerably in size, shape, color, and number, but generally it is easy to distinguish the pistil from the stamens. Stamens can be identified by the yellow powder (pollen) on their tips and the pistil by the bulge (ovary) at its base. However, in unusual flowers this may require careful study to distinguish them.
Types of Flowers
Flowers are classified according to the arrangement of sexual organs (by sexuality), i.e., according to the presence of male and female reproductive organs. They are divided into bisexual (monoclinous) and unisexual (diclinous - male and female).
Bisexual flowers contain both stamens and pistil in the flower (Figure 1). This is the most common type of flower. Common bisexual flowers include tomatoes, morning glory, snapdragon, petunia, lily, and iris.
Unisexual flowers contain either only stamens (male flowers) or only pistil (female flowers) (Figure 3).
Figure 3: Pumpkin flowers are imperfect, each flower has only one type of sexual organ
Those that have a pistil are called female flowers and those that contain stamens are called male flowers.
Unisexual flowers are further divided into monoecious (male and female flowers are on one individual - "house"; e.g., corn, pumpkin, clematis, bittersweet nightshade, begonia) and dioecious (male flowers and female flowers are on separate plants; e.g., willow, Cannabis sativa, asparagus, spinach, cotton).
Figure 4: Cross-section of a chrysanthemum. Polygamous flowers, such as chrysanthemums, are formed by clusters of flowers. Some polygamous flowers have both ray and disc florets, while some flowers have only ray florets.
If both unisexual and bisexual flowers occur on a single species, the plant is polygamous (e.g., ash tree). A polygamous flower (Figure 4) is actually a cluster of small flowers. These florets often resemble petals. Some florets have both stamens and pistils; they are called disc florets. Some have only pistils and are called ray florets. Typical polygamous flowers are rudbeckia, chrysanthemums, asters, and calendula.
Pollination and Fertilisation
For pollination, we need just a little time, knowledge, and a sensitive hand to replace the bees.
Pollination is the transfer of male plant cells (pollen) to the female organs of the flower (stigma). Pollination is a necessary prerequisite for seed formation to occur later. When the anther is mature, it splits open and releases pollen. The pollen is then transferred to the stigma by various natural means, the most common being wind, water, and insects. In plant breeding, pollination is carefully controlled by humans.
There are two types of pollen transfer – self-pollination and cross-pollination. In cross-pollination, pollen is transferred from the anther of a flower on one plant to the stigma of a flower on another plant. In self-pollination, pollen is transferred from the anther to the stigma of the same flower or to another flower on the same plant (e.g., beans, peas). Cross-pollination usually results in much larger yields.
The parent flower that provides the pollen is called the stamen; the flower that bears the seed is called the carpel.
Fertilisation is the union of two germ cells. After pollination, which is the transfer of pollen from the anther to the surface of the stigma, pollen grains attempt to reach the ovule by forming a pollen tube.
The pollen tube must grow through the entire length of the style, which is located in the pistil between the stigma and the ovary. Eventually, it penetrates through the micropyle to the embryo sac. One of the sperm cells fertilises the egg cell, which transforms into a diploid zygote, while the other fertilises the diploid central cell of the embryo sac, forming the basis of the triploid nutritive tissue of the embryo, the endosperm. The endosperm is used as a source of nutrients during germination or is consumed during embryo development. Its nutritional function can then be taken over by cotyledons, for example in leguminous plants. In angiosperms, the nutritive tissue forms only after fertilisation, while in gymnosperms it forms independently. The fruit develops.
Heredity
Plants inherit traits from their parents in the same way as animals. The laws of heredity explain why offspring inherit different characteristics (traits) from the same parents. Moreover, these laws allow us to predict the number of offspring that will inherit a particular trait. Knowledge of the laws of heredity is essential for effective plant breeding.
Genes. All cells contain genes, which are units that determine the characteristics of a plant or animal. Except for germ cells, each cell in a plant contains two genes for each trait - for example, for the color trait, a plant may have one gene for yellow and one for red. Germ cells have only one gene for each characteristic. Of the thousands of germ cells that a plant produces, approximately half have one of the genes for each trait and approximately half have the other gene.
When male and female germ cells merge in an egg, each contributes one gene for each trait, so the new seed has two genes for each characteristic. Different combinations of many genes inherited from the male sex and from the female sex determine the traits of offspring and future generations.
By looking at plants, you cannot tell exactly what genes they contain. For example, a plant may have one gene for red and one for yellow, but only its red color may be displayed on this flower; by looking at the plant, you cannot have any idea about the yellow color gene. Nevertheless, this yellow gene is present in the plant's cells and some of the plant's offspring may inherit this gene and then pass it on to their descendants. If the plant and its offspring are self-pollinated, in the first or second generation, depending on how the genes interact with each other, some offspring will produce yellow flowers.
By observing the phenomena of various offspring of different colors (or other characteristics you are interested in), you can learn what genes the parent plants had and how they interact with each other. With this knowledge, your breeding work will be considerably simplified.
If a plant that is self-pollinated produces offspring identical to itself, then it is called a true variety. If the offspring of the first generation are not identical to the parent plant, then it is said that segregation has occurred.
General Breeding Techniques
The equipment needed for plant breeding is relatively inexpensive and easy to use. Here are some items you may find useful:
Magnifying glass (power 10 or 15)
Tweezers
Scalpel
Small pointed scissors
Fine-haired brush
Small containers or vials
Alcohol
Rubber bands or soft wire
Paper or cellophane bags
Paper clips
Label
Notebook
When to Breed
The steps before pollination should generally begin just before the flower opens. If you wait until the time it opens, it may be pollinated naturally, which causes the flower to be unusable for experimentation. But since most plants flower for a certain period of time and some flowers on the plant bloom earlier, before you start breeding, there will probably be other flowers on the plant that have not yet opened and you can still experiment with the plant.
Preparing the Flowers
When the plant has produced a sufficient number of flowers, we choose a late afternoon and prepare them. We must distinguish between male and female types. Female flowers already have a visible base of the future fruit below the flower (for example, in courgettes, an elongated cylinder or miniature courgette), they have a shorter stem and there are usually fewer of them than male flowers. Male flowers have a longer stem, do not bear fruit, and in classic varieties, they are in the majority. Flowers that are due to bloom the next day are already fully developed in the afternoon and have a slightly opening tip at the top. Such a male flower, suitable for pollination ("ripe"), is carefully taped with crepe adhesive tape or clamped with a clothes peg. We do the same with female flowers. In this way, for one female flower from one plant, we prepare several male flowers from other plants.
Extremely high temperatures or humid conditions are harmful to pollen. To achieve the best results, you should pollinate plants on dry days in cool morning hours, or as soon as the anthers are in bloom.
Selecting Parents
Some plants have natural barriers that prevent cross-pollination or self-pollination. It is recommended to verify this before you start breeding the plant, because even though it is often possible to overcome these barriers, some plants cannot be artificially pollinated. An example of a barrier that can be overcome is the prevention of natural cross-pollination in snapdragon. Snapdragon flowers are constructed to prevent wind-borne pollen from other flowers from entering. However, it is possible to open the flower manually. An example of a barrier that cannot be overcome is self-pollination, which is prevented in some orchids. The stigmas of some orchids produce a substance that kills the pollen of flowers from the same plant. The mechanism that performs this function cannot be removed without removing the pistil.
Plants that are selected for breeding should be robust and healthy. It is usually easier to determine which ones are healthy after several flowers have bloomed on the plant.
When selecting according to the male plant cell (pollen), it is good to choose one that has heavy yellow powder on the anther. This powder is pollen. If you scratch your nail against the anther, a trace of pollen should remain on the nail. A fresh flower is more likely to have healthier pollen than a flower that has started to wilt or dry out.
When selecting according to the female organ of the flower, test the stigma. It should either have a shiny substance that is sticky to the touch or has a "hairy" surface. This is the substance or surface that captures pollen, allowing fertilization.
After you have selected a plant according to pollen and stigma, you are ready to start pollinating.
Steps Before Pollination
The first step is to mark those flowers that are to serve as male plant cells (pollen) and those that are to serve as female flower organs. This can be done, for example, with coloured thread, one colour for male and another colour for female.
Figure 5: It is necessary to prevent self-pollination by removing all anthers or stamens
The next step is to protect the plant from unwanted pollen. If the plant is to be cross-pollinated, its stamens must be removed to prevent the possibility of self-pollination. The removal of stamens is called castration. This should be done before the anthers open and release pollen. This may require opening the flower by hand before it is ready to bloom. Castration can be performed by pulling off the stamens or anthers using tweezers (Figure 3), or by cutting off the stamens or anthers with sharp pointed scissors, or by removing the petals to which the stamens are sometimes attached. A magnifying glass will be especially useful during castration.
Both reproductive organs should be protected from contamination by foreign pollen. This can be done in one of the following ways:
Closing the flower. In many flowers, such as bindweed, petunias and lilies, the petals around the flower organs can be closed with a piece of soft wire or rubber band (Fig. 11). Care should be taken not to tear the petals.
Figure 6: Protecting the flower from unwanted pollination by tying (left) or covering with a bag (right)
To protect the flower from unwanted pollination, close the flower using soft wire or a rubber band (Figure 4 left) or cover it with a bag (Figure 4 right). Cellophane or plastic bag will allow you to monitor the flowers throughout.
Flowers that are to be self-pollinated should also be protected from foreign pollen, either by closing or covering the flower.
If the plant is grown indoors, there is little chance of contamination by foreign pollen and you do not need to cover or close the flower. However, both indoor and outdoor plants require castration to prevent self-pollination.
Pollination Steps
Figure 7: One way of cross-pollination is to remove the stamens with pollen and then hold the stamens with tweezers and brush the anther over the stigma.
- Cross-pollination. There are several methods that can be used for cross-pollination of flowers. Here are the four most common methods:
1. Remove the stamen with pollen using tweezers. Place the stamen in a small container. Expose the pistil by carefully removing the petals and sepals from the selected bud using scissors. Early castration not only exposes the pistil but also prevents self-pollination. Hold the stamen in the tweezers above the exposed stigma and gently brush the anther across the female flower organs (stigma) (Figure 5).
2. Cut off the flower that serves as the male plant cell (pollen). Expose the stigma. Using tweezers, remove the stamen from the cut flower and gently rub the anther across the female flower organs (stigma).
3. Using a brush, transfer pollen from the anthers (male plant cells) into a small container. Remove the protection from the stigma and wipe the pollen onto the stigma (Figure 6). Then replace the protective cover.
Figure 8: If the stamens are too small or difficult to grasp, you can perform cross-pollination by transferring pollen from the anthers with a brush into a container and then rubbing the stigma with pollen
4. Place the removed stamens in a bag and shake it. Take the stamens out of the bag and be careful not to spill the pollen. Remove the protection from the stigma and place the bag containing pollen above the stigma and shake the bag so that the pollen falls onto the stigma surface. This method is commonly performed with corn.
Whenever you work with different pollens, always thoroughly clean the brush, tweezers, and other items that might come into contact with any pollen with alcohol first. This step is very important to prevent pollination of the female reproductive organ with unwanted pollen that may have caught on the object. After washing the tools, make sure they are dry again before use.
- Self-pollination. The procedures for self-pollination of flowers will depend on the flower species. For perfect flowers, your work is done once you close or cover the flower. However, sometimes you can help the pollen fall and attach to the stigma by shaking the flower once daily for several days after the flower has opened.
Only composite flowers that contain both disc and ray flowers can be self-pollinated. Since they have both pistils and stamens, they can be self-pollinated in the same way as hermaphroditic flowers.
With unisexual flowers, self-pollination will only be possible for those flowers that are on the same plant. For self-pollinating unisexual flowers, pollen from the stamens of one flower must be transferred to the stigma of a pistil flower from the same plant. To do this, you can use any of the cross-pollination methods mentioned above.
Post-Pollination Steps
Immediately after pollination, close or cover the flower again. Label the pollinated fruit right away. We mark the pollinated fruit so we can identify it later. For example, tie a colored piece of cloth around the stem, but not too tightly, as the stem expands as the fruit grows.
Observing the Results
Once the pollination phase is complete, time must pass for fertilization to occur and for the subsequent development of the fertilized egg. When the seed is fully developed, it should be harvested. In plants grown for flowers, seeds are harvested as soon as they are dry, or just as they begin to open. In fruits and vegetables, the seed will be fully developed and ready for harvest when it has reached maturity in the seed portion.
When harvesting seeds, place them in packets bearing the assigned offspring number. Be careful to store seeds from different cross-pollinations and self-pollinations in separate packets. Allow the seeds to dry in a relatively warm place for about one week, then store them in a cool, dry location.
As soon as possible, the seeds should be planted and the results recorded in your record book. The offspring can be used for further study. Any seeds that are not planted should be kept in case of an unfavorable crop.
Breeding Experiments You Can Try
The following crops have been selected as examples of different types of flowers that occur in plant breeding - hermaphroditic, unisexual, and polygamous. The suggested techniques, with minor modifications, can be used for crossing other plants with similar flowering systems.
Corn (Maize)
Corn is an excellent plant for amateur plant breeders to experiment with because it is easy to work with and visible changes in the kernels of the F1 generation often occur. Varieties you can work with include yellow field corn, white field corn, sweet corn, calico corn, and strawberry corn.
Figure 9: Corn has unisexual flowers. Staminate (male) flower and pistillate (female) flower.
Corn has unisexual flowers, with both flowers (male and female) on the same plant (Figure 7). The male staminate flowers are concentrated in the terminal tassel; the female flowers occur only on lateral ears. The stigma, which has a hairy surface for most of its length, is receptive to pollen.
Procedure:
1. Choose the corn varieties you want to cross and sow the seeds at your experimental site. You can work with as many variants as you wish, but if this is your first experiment, it's best to focus on just three or four. Corn loses its pollen in a relatively short time, so to ensure the pollen of different varieties is ready at approximately the same time, plant several seeds from each variety repeatedly over several weeks and mark the rows for future use.
2. Once cob shoots begin to develop on the plant, before the silks appear, cover the shoots with a loosely fitted bag, secured at the bottom with a paper clip or string. A transparent plastic bag will allow you to monitor silk development. Cover several cob shoots, because the more that are pollinated, the greater your chances of obtaining the desired results.
3. Watch the cobs carefully. When the silks are visible, the cob is ready for pollination. The corresponding tassels should then be covered with a bag and prepared for use the following morning. The bag should be placed on the underside of the tassel to prevent pollen from falling out and to avoid mixing with other pollen.
4. The following morning, shake the bag thoroughly to release the pollen into it. Remove the bag from the tassel in a downward-bent position to prevent pollen spillage (Figure 8).
Figure 10: When collecting corn pollen, bend the tassel downward to prevent pollen from spilling out of the bag
Then remove the bag covering the silk. Place the bag from the tassel onto the cob, taking care not to spill the pollen. Secure the bag to the stalk below the cob and shake it (Figure 9).
Figure 11: Place the bag containing pollen onto the corn cob, attach the bag to the stalk below the cob, and label the pollinated cob with a tag
5. Label each cob that was pollinated with the name or number of the plants that served as female and male organs, and record the crossing in your notes.
6. Leave the bag on the plant's cob until the leaves dry. After the pollinated cob has dried, record all changes that occurred in the kernels.
Pumpkins
Pumpkin flowers are large and easy to work with. The flowers are unisexual, with both male and female flowers on the same plant. The pistil of the flower is enlarged at the base, while the staminate flowers are positioned on a long stalk (see Figure 3).
Although some pumpkin or squash varieties are pollen-sterile for crossing, meaning they cannot be crossed, many others can be crossed. It is also possible to cross certain species of pumpkins and squashes.
Remember that if you cross pure varieties, segregation will not occur until the F2 generation, meaning that the different colors and shapes that the offspring inherited will not all be visible until self-pollination occurs and the seeds begin to produce fruits.
In other words, you cross in the first year. In the second year, you sow the crossed (so-called F1 hybrid) seeds. Plants in the F1 generation tend to be quite uniform. Therefore, do not select in the second year and just harvest seeds from all plants. Only in the third year, in the F2 generation, will the genetic differences between individual plants fully manifest, and the time comes for observation, comparison, and selection. In the third year, keep seeds only from those plants that best match your vision of the new variety. Be attentive and open to something new or unusual. You can still adjust your variety idea. In the following years, remove all plants that do not match your idea of the new variety. The variety will stabilize, and after four to six years of selection, you can offer the world something completely new.
Procedure:
1. Plant different types of pumpkins/squashes. Mark the individual rows so you know which plants should be the female sexual organs and which should be the male sexual organs. You will have no trouble with the male and female sexes being ready for pollination at the same time, as these plants produce flowers for quite a long period.
2. In the evening, before the flowers open, put a bag over them or close the flowers with a rubber band or string (see Figure 4). In the evening hours, it is easy to determine which flowers will open the following morning. The flowers will be slightly open, revealing the inner color, which is lighter than the color on the outer side of the petals. Both (pistillate and staminate) flowers must be protected to prevent bee access.
3. Early in the morning on the day the flowers open, remove the stamens from the staminate flower and gently rub the anthers over the stigma of the pistillate flower. (Figure 11)
Figure 12: To pollinate a pumpkin, gently rub the anther over the stigma of the pistillate flower
4. Replace the bag on the pistillate flower.
5. Mark this pollinated female flower and make a note in your records.
6. When the petals dry out or when the ovary bulges through the bag, you can remove the protective covering on the female flowers.
7. When the fruits are ripe, harvest the seeds (Fig. 19). Fruits usually ripen approximately 45 days after pollination. Store the seeds until next year, when (1) you plant them, (2) self-pollination of the resulting flowers occurs, and (3) you harvest the seeds again. A year after planting the seeds produced by self-pollination of the F generation, segregation will likely occur.
Figure 13: Harvesting pumpkin seeds and storing them for planting next year
Tomato
Figure 14: Reproductive parts of tomato
Tomatoes have a perfect flower with both male and female reproductive cells on the same flower (Figure 13). The reproductive organs are easily recognizable, making tomato crossing relatively easy. For this experiment, select tomatoes with two different fruit colours, such as red and yellow. If the tomatoes are pure varieties, differences in colour will be visible in the F2 generation. Along with different colours, changes in fruit shape and other plant characteristics are likely.
Procedure:
1. Plant seeds or young plants and label individual rows so you know which plants will produce red fruits and which will produce yellow fruits. Tomatoes flower for several weeks, so you won't have any trouble ensuring both buds are at the same stage and both reproductive organs are ready at the same time.
2. Once the flowers that will serve as mating varieties begin to open, castration should be performed on the plants. The tomato flower has a pistil fused with the stamens, the male reproductive organs, in such a way that the pistil is completely enclosed between them and often not visible at all. Therefore, we must first expose the pistil by using scissors to remove the petals and sepals from the selected bud. Then, with a scalpel, we longitudinally cut the fused stamens and gradually remove them.
3. Both varieties, pollen and seed, that you want to use should be at the same stage of opening. After removing the stamens, cover both varieties simultaneously with a bag to prevent self-pollination.
4. Once you have an exposed pistil on one variety, transfer pollen from the other variety onto its stigma, which is located at the tip of the pistil. Hold the stamen in tweezers above the stigma and gently brush the anther across the female flower organs (stigma).
5. Replace the bag that was removed from the pollinated flower.
6. Label the flower that was pollinated (Figure 14) and note everything in your records.
Figure 15: Tomato flower that has been emasculated, pollinated and labelled
7. After one week, remove the bag covering the pollinated flower and leave it exposed.
8. Once the fruits ripen, harvest them and save the seeds for future planting and self-pollination (Figure 15).
Figure 16: Harvesting and storing tomato seeds for planting next year
Chrysanthemums
Chrysanthemums are polygamous flowers. If you don't have chrysanthemums available for breeding, you can use any other polygamous flower, such as asters or China asters. Polygamous flowers are more difficult to cross than hermaphroditic or unisexual flowers. If you're breeding plants for the first time, it would be better to gain experience by starting first with simpler plants, such as pumpkin, squash, iris or lily, before attempting to cross polygamous flowers.
Procedure:
1. Plant seeds or young plants. Chrysanthemums, asters and China asters bloom for quite a long time, so you won't have any difficulty ensuring that both buds are at the same stage and both reproductive organs are ready at the same time.
2. Immediately after the flower with the carpel opens and before the pollen is mature, remove the disc florets with tweezers. As shown in Figure 4, the disc florets are in the centre of the flower. They are easily identifiable because they are often yellow and have both reproductive organs - pistil and stamens - while the ray florets surrounding the disc have only pistils. Remove some ray florets near the centre of the flower, just to make sure you haven't missed any of the disc florets. If any disc florets remain on the flower, they are likely to self-pollinate (Figure 17).
Figure 17: When emasculating chrysanthemums, make sure you have removed all disc florets
3. After removing the disc florets, cover the female organs of the flower with a bag.
4. Once the flowers with male reproductive organs open, cover them with a bag.
5. Pollination will be more effective if you trim the ray florets on the female organ just above the stigma. This step can be performed at any time after the disc florets are removed and before pollination is carried out (Figure 18).
Figure 18: Trimming ray florets for more effective pollination
6. The flower is ready for pollination approximately four or five days after it opens. Shortly before pollinating the flower, dip the fine-haired brush into alcohol and let it dry.
7. Remove the flower with the male organ. Using the fine-haired brush, gently brush the disc of the pollen flower. The pollen should adhere to the brush. Then gently wipe the trimmed ray flowers of the pistil (see Figure 8). Each time you change the flower with male organs, dip the brush into alcohol and let it dry.
8. Replace the protective bags on both the male and female organ flowers.
9. Label the pollinated flower and make a note of the cross in your records.
10. Three or four days later, repeat step 7. Make sure you use pollen from the same flower with male organs that you used the first time. Replace the bag on the pistil.
11. About a week after the last pollination, remove the bag from the pistil.
12. After the pistil head dries, harvest and store the seeds (Figure 19).
Figure 19: Each mature ray flower will have a seed. Harvest these seeds and plant them next year.