Today there is an incredible variety of fruits. And what a difference in taste! There are wild apples that can be described as "so sour that they take the edge of the knife", words that the natural scientist Plínio used about two thousand years ago. But many other varieties of apples are delicious for their taste and the options are not limited to a few. Why are 1823 different varieties included in a fruit book published in the United States more than a hundred years ago? But all with their characteristics are descendants of common ancestors. In fact, the new types of fruit come from old varieties. How was it obtained?
Probably, when men gained agricultural experience, they were more selective with the seeds they saved for future planting and chose the seeds of the largest grapes, the sweetest apples. , larger olives, etc. This gradually produced more and more different species of wild varieties.
The deliberate crossing to combine the desirable characteristics of different parents is a new development. Growing new types of old fruit in this way is not always easy, as Professor L. H. Bailey discovered in the late 19th century.
Bailey stood in the autumn with a mountain compass and pumpkin from Bergen and stretched the offspring with a pumpkin. In 1891, the fruits of this second generation resembled those of Bergen, with a thin, papery skin on a thick and attractive yellow mass. The peel protected the fruit from rough handling and ice. The meat cooks well. "But the taste," shouted Bailey, "remnants of quinine, bile and bones! The pumpkin was still there.
Since then, the man has learned a lot. There are at least five ways to produce better fruit.
sports
One solution is to use "sports". For a plant grower, sports are isolated plants that in some way differ significantly and in a new way from the original type. How were they last born?
Perhaps one in two hundred thousand times the mechanism by which genes reproduce a little fails. This may be due to exposure to radiation, heat or chemicals. The resulting genetic change is a "mutation". Most mutations are recessive and therefore do not appear immediately. But over time, a recessive mutation can manifest itself as a new trait. This new feature may be attractive enough to attract attention (like double flowers) and is still considered worthy of preservation, despite its low reproductive potential. Plants with this altered trait are the "sport" of the breeding world. If new features only appear on a bud or branch, it is called budding. Seeds from plants with genetic changes are also affected, and therefore the new feature can be retained.
Selective selection of hybrids
Another way to improve fruit varieties is to create hybrids. This method developed an apple tree that could survive the cold winters of northwestern Canada. In 1887, Dr. Saunders began creating plants from a small Siberian apple tree (Malus baccata) that can withstand temperatures of -34 degrees Celsius. Seven years later these plants flourished and he crossed them with sweet and cultivated varieties. The most promising of the eight hundred plants stood up to the harshness of northwestern Canada and survived. Over time, they also flourished and Dr. Saunders, who was not afraid of the small size of the fruit, used them to make various crosses with cultivated species. Among the descendants were some with the large, sweet fruits of their cultivated parents and the robustness of their Siberian ancestors.
Crosses innate lines
Another important way to produce new varieties of fruit from old ones is to cross clean lines for hybrid power. Many mutant genes may have accumulated in some food plants over the centuries and weakened these plants. This is because inbreeding increases the likelihood that the recessive traits carried by mutant genes will manifest in the offspring of plants, leading to a gradual loss of power and consequent yield. The combination of two of these innate lines restores the effectiveness to an amazing level; This is even more true when four unrelated bloodlines are combined in two generations. This improvement is only possible with some plants, but with maize or maize the effect is phenomenal.
Double the number of chromosomes
A fourth way to make new fruits from old ones is to double the number of chromosomes. The normal contribution of each parent's gamete chromosomes is half a set (the haploid number). After fertilization, they together form the diploid number of chromosomes in each cell. For almost all animals and most plants, this is the normal number of chromosomes. However, plants can have more chromosomes and still be healthy specimens. Those with three, four, five, six, seven, or eight chromosomal agents are triploid, tetraploid, pentaploid, hexaploid, heptaploid, and octoploid, respectively. Plants like these are generally larger and more powerful, but less fertile than diploids. For example, a cultivated red pepper (tetraploid) has an average of four times more weight than its diploid relatives. The fruit is up to five hundred times heavier!
In order to form haploid gametes from the diploid cells of the body, the chromosomes pair like two rows of partners in a dance. Hence, four cells are formed from one original cell, each of which has only the haploid number of chromosomes. If more than two cells consist of similar chromosomes, one or more chromosomes generally cannot find a mate (inevitably if the stem cell is triploid, pentaploid or heptaploid). Even in tetraploid cells, chromosomes can be separated by three and one instead of two and two. This imbalance tends to be sterile. But even if 5% of female gametes are fertilized, it is enough to produce fruit.
By applying colchicine to fast-growing shoots, chromosome doubling can almost be achieved today. X-rays can also be used to selectively kill the remaining diploid cells.
A combination of hybridization and chromosomal duplication.
The fifth way to get new fruits from old ones combines the hybridization of species with the replication of chromosomes. When less closely related plant species are crossed, the offspring are usually strong but sterile. Duplicating chromosomes with the help of colchicine restores fertility, usually at its best.
Nothing new in the absolute mood
However, we must not think that the breeders just have to choose suitable parents and pollinate, and then we will have a new juicy fruit. Sometimes years of hard work, at best thousands of plants later, can only result in a new strain that is no better than the previous one. There are many disappointments. Also, not all new varieties are as nutritious as the old ones. For example, white cabbage contains less vitamin A and vitamin C than green hearts. Cabbage is denser, harder, and less digestible.
Our modern understanding of genetics leads us to realize that, in the end, humans did nothing new through their reproductive efforts. In any theoretical development there has been much less natural selection or blind chance. All honor must go to the Creator, who gives plants the potential to survive for generations in nature and to develop them from humans into a wonderful variety. Therefore, in making new types of fruit from old ones, humans have simply explored the potential that has existed since plants emerged.
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