The most promising approach to solving the world food problem is, apparently, the further improvement of existing crops grown on already developed lands. Hybrids are something that can play a key role in food security. After all, most of the areas suitable for agriculture are already occupied. At the same time, increasing the amount of water, fertilizers and other chemicals used on them is not economically feasible in many places. That is why the improvement of existing crops is of exceptional importance. And hybrids are plants obtained just as a result of such an improvement.
Protein content
The goal is not only to increase yields, but also to increase the content of protein and other nutrients. For a person, the quality of proteins in edible plants is also very important: animals (including people) must receive from food the right amounts of all essential (i.e., those that they are not able to synthesize themselves) amino acids. Eight of the 20 amino acids needed by humanscome with food. The remaining 12 can be developed by him. However, plants with an improved protein composition as a result of selection inevitably require more nitrogen and other nutrients than the original forms, so they cannot always be grown on infertile lands, where the need for such crops is especially great.
New properties
Quality includes not only yield, composition and quantity of proteins. Varieties are created that are more resistant to diseases and pests due to the secondary metabolites they contain, more attractive in shape or color of fruits (for example, bright red apples), better able to withstand transportation and storage (for example, tomato hybrids of increased keeping quality), and also possessing other properties essential for a given culture.
Activities of breeders
Breeders carefully analyze the available genetic diversity. They have developed thousands of improved lines of the most important agricultural plants over the course of several decades. As a rule, thousands of hybrids have to be obtained and evaluated in order to select those few that will actually outperform those already widely bred. For example, US corn yields from the 1930s to the 1980s increased by almost eight times, although only a small part of the genetic diversity of this crop was used by breeders. There are more and more new hybrids. This allows more efficient use of crop areas.
Hybrid corn
Improving maize productivity has becomemade possible mainly by the use of hybrid seeds. Inbred lines of this culture (hybrid in origin) were used as parental forms. From seeds obtained as a result of crossing between them, very powerful hybrids of corn develop. Crossed lines are sown in alternating rows, and panicles (male inflorescences) are manually cut from the plants of one of them. Therefore, all seeds on these specimens are hybrid. And they have very useful properties for humans. By careful selection of inbred lines, powerful hybrids can be obtained. These are plants that will be suitable for growing in any required area. Since the characteristics of hybrid plants are the same, they are easier to harvest. And the yield of each of them is much higher than that of unimproved specimens. In 1935, corn hybrids accounted for less than 1% of all that crop grown in the United States, and now virtually all. It is now much less labor intensive to achieve significantly higher yields of this crop than it used to be.
Success of International Breeding Centers
During the past few decades, much effort has been made to increase the yield of wheat and other grains, especially in warm climate zones. Impressive success has been achieved in international breeding centers located in the subtropics. When new hybrids of wheat, corn and rice developed in them began to be grown in Mexico, India and Pakistan, this led to a sharp increase in agricultural productivity, called the Green Revolution.
Green Revolution
The methods of breeding, fertilization and irrigation developed during it have been used in many developing countries. Each crop requires optimal growing conditions to obtain high yields. Fertilization, mechanization and irrigation are essential components of the Green Revolution. Due to the peculiarities of the distribution of credits, only relatively we althy landowners were able to grow new plant hybrids (cereals). In many regions, the Green Revolution accelerated the concentration of land in the hands of a few of the we althiest owners. This redistribution of we alth does not necessarily provide jobs or food for the majority of the population in these regions.
Triticale
Traditional breeding methods can sometimes lead to surprising results. For example, a hybrid of wheat (Triticum) and rye (Secale) triticale (scientific name Triticosecale) is gaining importance in many areas and appears to be very promising. It was obtained by doubling the number of chromosomes in a sterile hybrid of wheat and rye in the mid-1950s. J. O'Mara at the University of Iowa with colchicine, a substance that prevents cell plate formation. Triticale combines the high yield of wheat with the ruggedness of rye. The hybrid is relatively resistant to line rust, a fungal disease that is one of the main factors limiting the yield of wheat. Further crosses and selection have yielded improved triticale lines for specificdistricts. In the mid 1980s. this crop, thanks to its high yield, resistance to climatic factors and the excellent straw remaining after harvest, quickly gained popularity in France, the largest grain producer within the EEC. The role of triticale in the human diet is growing rapidly.
Conservation and use of crop genetic diversity
Intensive crossbreeding and selection programs lead to a narrowing of the genetic diversity of cultivated plants for all their traits. For obvious reasons, artificial selection is mainly aimed at increasing productivity, and among the very homogeneous offspring of specimens selected strictly on this basis, resistance to diseases is sometimes lost. Within a culture, plants become more and more uniform, as certain of their characters are more pronounced than others; therefore crops as a whole are more vulnerable to pathogens and pests. For example, in 1970, helminthosporiasis, a fungal disease of corn caused by the Helminthosporium maydis species (pictured above), destroyed approximately 15% of the crop in the United States, causing a loss of approximately $1 billion. These losses seem to be related to the emergence of a new race of the fungus, which is very dangerous for some of the main lines of corn that were widely used in the production of hybrid seeds. Many commercially valuable lines of this plant had identical cytoplasms because the same pistil plants are repeatedly used in hybrid corn.
To prevent thisdamage needs to be grown in isolation and to conserve different lines of critical crops that, even if the sum of their traits is not of economic interest, may contain genes useful in ongoing pest and disease control.
Tomato hybrids
Tomato breeders have made astonishing progress in increasing genetic diversity by attracting wild varieties. The creation of a collection of lines of this culture, carried out by Charles Rick and his collaborators at the University of California at Davis, made it possible to effectively deal with many of its serious diseases, in particular those caused by imperfect Fusarium and Verticillum fungi, as well as some viruses. The nutritional value of tomatoes has been significantly increased. In addition, plant hybrids have become more resistant to salinity and other adverse conditions. This was mainly due to the systematic collection, analysis and use of wild tomato breeding lines.
As you can see, interspecific hybrids are very promising in agriculture. Thanks to them, you can improve the yield and quality of plants. It should be noted that crossbreeding is used not only in agriculture, but also in animal husbandry. As a result of it, for example, a mule appeared (its photo is presented above). This is also a hybrid, a cross between a donkey and a mare.
