Since ancient times, people have been fascinated by the beauty and variety of surrounding plants, especially flowers. Over all centuries, their fragrance and tenderness have been the personification of love, purity, and the manifestation of feelings. Gradually, a man realized that he could not only enjoy the existing forms of these beautiful creatures, but also take part in their formation. Thus began the era of plant breeding, leading to the production of new species that have more necessary and important traits in the geno- and phenotype. The two sciences working together on this issue have so far managed to achieve simply fantastic results - genetics and botany.
The subject of study of botany
Botany is a science that studies everything related to plants. That is them:
- morphology;
- genetics;
- physiology;
- anatomy
- taxonomy.
This discipline covers all aspects of the life of flora representatives, starting with the internal processes of respiration, reproduction and photosynthesis and ending with the external variety of phenotypic characters.
This is one of the most ancient sciences, which appeared along with the development of man. A person has always been interested in creatures growing around him, so decorating the surrounding space. In addition, in addition to beauty, at all times it was also a powerful source of food, medicinal components, and building material. Therefore, botany is a science that studies the most ancient, important, diverse and complex organisms on our planet - plants.
Plant breeding
With the passage of time and the accumulation of theoretical knowledge about the structure of these creatures from the inside, their lifestyle and the processes taking place in them, an understanding of how their growth and development can be manipulated has become available. The science of genetics was gaining momentum, which made it possible to study different objects at the chromosomal level, cross them together, get good and bad results, and choose the ones that were beneficial and necessary. This was made possible thanks to the following discoveries.
- Double fertilization in plants.
- The discovery of mitosis and meiosis.
- Development of crossbreeding methods.
- Phenomena of heterosis, outbreeding, and inbreeding.
- Deciphering the genetic code of plants.
- Biomolecular studies of the composition of cells and tissues.
- Discoveries in the field of cytology and histology.
Of course, this is not all the prerequisites that served as the beginning to a powerful movement and the development of breeding methods for working on plants.
Crossbreeding and its characterization
Another name for the crossing process is hybridization. The method of using this phenomenon is called hybridological. The first to use it for his experiments was Gregor Mendel. Every schoolboy knows his famous experiments on peas.
The essence of the whole process is the interbreeding of parental forms in order to obtain heterozygous progeny, which will be called a hybrid. At the same time, different types of crossing are developed. They are selected taking into account the individual characteristics of the variety, species or genus. In total, there are two main types of such processes.
- Outbreeding, or unrelated crossbreeding. It implies that the initial parental forms do not belong to the same species, genus or variety. That is, they do not have family ties. This crossing is one of the most popular and most often leads to heterosis in the development of clean lines.
- Inbreeding, or inbreeding, is a closely related hybridization of individuals belonging to the same species or genus, variety. This method is used to fix in the population any useful trait, including phenotypic. With repeated correctly carried out incuht, it is possible to obtain genetically pure plant lines.
These types of crosses have narrower varieties within themselves. So, crossbreeding is considered one of the forms of outbreeding - hybridization between varieties.
In addition to types, there are also different types of crosses. They were described and studied in detail by Mendel, Thomas Morgan and other geneticists of past centuries.
Types of Crossing
There are several main types of hybridization of individuals.
- Monohybrid, or simple. It implies the crossing of parental forms with the receipt of the first offspring, carried out once.
- Hybrid - parents based on two pairs of signs are taken as the basis.
- Returnable - A hybrid from the first generation interbreeds with the original parent.
- Polyhybrid, or double - individuals of the first generation are then crossed with each other, and subsequent with other varieties and species.
All designated varieties matter in each specific situation. That is, for some plants, simple crossing is enough to get the desired result. And for others, a complex stepwise polyhybrid hybridization is required to obtain the desired trait and fix it in the entire population.
Hybrids of different generations
As a result of any crossing, this or that offspring is formed. The features that it took from the parents are capable of manifesting themselves in varying degrees.
Thus, the signs of first-generation hybrids are phenotypically always uniform, which is confirmed by Mendel’s law (first) and his experiments on peas. Therefore, often to obtain the same result, which is required only at a time, it is precisely the mono-hybrid type of hybridization that is used.
Further, all subsequent individuals already combine properties in themselves, therefore, splitting appears in certain ratios. Recessives appear, mutational processes interfere . Therefore, the most important generation of plants is the most important for the industrial activity of man, his agriculture.
A typical example: if the goal is to obtain only yellow tomatoes as a result of one seasonal period, then the yellow and red tomatoes should be crossed, but the red must be obtained earlier from the yellow parent. In this case, the first generation will certainly be the same - the yellow fruits of tomatoes.
Intraspecific hybrids: characteristic
Interspecific are those hybrids that are obtained as a result of outbreeding or distant crossbreeding. That is, this is the result of mating individuals belonging to different species in order to obtain a new one with predetermined characteristics and properties.
In this way, many important agricultural and ornamental plants were obtained in industry by humans, and many new species of animals were bred in animal breeding.
Examples of similar organisms
Examples of interspecific hybrids among plants:
- grain feed wheat;
- triticale - wheat and rye;
- rye-wheatgrass forms;
- Wheat Elimus
- several types of tobacco and others.
If we talk about animals, then many representatives can also be cited as an example:
- hinnies (horse and donkey);
- liger - lion and tigress;
- Mezhnyak - black grouse and capercaillie and others.
The main problem of such hybridizations is that the offspring is either sterile or nonviable. That is why people created and developed a lot of ways to eliminate these factors. Indeed, if the desired result is obtained, it is very important not only to fix it, but also to introduce the receipt of such organisms into the system.
What is the cause of infertility of interspecific hybrids?
The causes of such problems lie in the processes of meiosis and mitosis, namely in anaphase, when the chromosomes diverge to the poles of the cell. At this moment, each of them is looking for its own homologous pair. Thus, entire chromosomes from chromatids are formed and the general karyotype of the organism is formed.
But for those individuals in whom the merger came from different parental forms, the possibility of meeting such structures is minimal or impossible. That is why there is a random combination of characters and as a result, individuals become infertile or nonviable. That is, genes, in fact, become incompatible.
If we turn to the molecular level and find out what is the reason for the infertility of interspecific hybrids, the answer will be this: this is the incompatibility of the DNA sections from the cell nucleus and mitochondria. As a result, there is no conjugation of chromosomes in the meiotic process.
This leads to disastrous results both in plant breeding and in breeding and breeding of breeds and new species of animals. Especially often this happens in representatives of the flora. Therefore, you can get a crop of hybrid plants only once, which is extremely inconvenient for the development of agriculture.
After it became clear to the scientists what was the reason for the infertility of interspecific hybrids, active work began on finding a way to eliminate these causes. This led to the creation of several ways to eliminate the sterility of individuals.
Ways to Overcome Infertility
The main path that biologists have chosen to solve this problem is as follows. At the stage of meiosis, when the chromosomes diverge to the poles of the cell, a special substance is introduced into it - colchicine. It contributes to the dissolution of the threads of the spindle division (cell center). As a result, all chromosomes remain in one cell, and do not fall into different ones. Now free conjugation between homologous pairs is possible, which means that it is a completely normal meiosis process in the future.
Thus, the offspring becomes fertile and easily bears fruit in the future when crosses with different forms. Most often, this method is used precisely in plant breeding; it has the name polyploidy. It was first applied by our scientist Karpechenkov. So he got the first fertile hybrid of cabbage and radish.
What is the reason for the infertility of interspecific hybrids, we have already found out. Knowing the nature of the problem, we managed to create two more ways to solve it.
- Plants pollinate the pollen of only one of the parents. This method allows you to get several generations of hybrid fertile individuals. However, then the sign still returns, and the individuals again become sterile.
- Pollination of hybrids in the first generation with the pollen of parents.
To date, more methods of struggle have not been created, but work in this direction is underway.
Lilies and their hybrids
A symbol of purity and innocence, flowers of sadness and sorrow for the departed, gentle and delicate representatives of lily - lilies. These plants are valued by man for many centuries in a row. During this time, what varieties were not created! Naturally, interspecific crossings also affected them.
The result was the breeding of nine groups of hybrid varieties that simply amaze with the beauty of phenotypic traits! Among them, a special place is occupied by two of the most unusual and sought-after representatives:
- eastern hybrids;
- Lilies OT Hybrids.
Consider the signs of both groups and give them a characteristic.
Oriental hybrids
This is the largest emerging hybrid flower. Their biology is practically no different from that of other representatives. The sizes of a growing cup can reach 31 cm in diameter, and the color can be different. The Nippon variety is very beautiful, having large white flowers with a pink fringing. The petals are corrugated.
The height of these plants ranges up to 1.2 m. This allows you to plant them at a distance of 20-25 cm from each other and form beautiful flowering ridges. All representatives of this group exude a very strong aroma.
Orienpits
These are lilies of OT hybrids, the abbreviation of which is formed from the full name: oriental-tubular forms. They are also called lilac trees for the very high size of plants and large flowers. Over 25 large (up to 30 cm) flowers that are very fragrant and brightly colored can form on one stem up to 2.5 meters high.
This allows this group of hybrids to be very popular among gardeners, although not everyone can cope with their breeding. Very careful care and proper planting is required so that such forms can take root and give offspring.
Sunflower and its hybrid forms
Sunflower hybrids differ from each other in terms of seed ripening. So, allocate:
- precocious (up to 90 days);
- early ripening (up to 100 days);
- mid-season (up to 110 days).
Seeds hybrids also produce uneven. Oil content and yield is excellent and depends on the maturity. The longer the plant is in the ground, the higher the quality of the crop. You can name some of the most common hybrids of this plant in the world, the most popular in agriculture.
- Tunka.
- Bosphorus.
- Rocky.
- PR64A15.
- Jason.
- Forward
Among their main advantages:
- resistance to drought;
- diseases and pests;
- productivity;
- high quality seeds;
- good fruiting.