Mutations in Plant Breeding
Artificially obtained mutant forms are valuable material for selection, since under controlled conditions it is possible to obtain mutations that are very rare or not detectable in nature. Mutagenesis is widely used in the selection of microorganisms and plants.
A variety of mutagens are used to produce induced mutations in plants. The dose of these mutagens is selected so that no more than 30-50% of the treated objects die. For example, when using ionizing radiation, such a critical dose is from 1-3 to 10-15 and even 50-100 kilo-roentgen. When using chemical mutagens, their aqueous solutions with a concentration of 0, 01-0, 2% are used; processing time – from 6 to 24 hours or more.
Processing is subjected to pollen, seeds, seedlings, buds, cuttings, bulbs, tubers and other parts of plants. Plants grown from treated seeds (buds, cuttings, etc.) are indicated by the symbol M1 (first mutant generation). Selection in M1 is difficult, since most mutations are recessive and do not show up in the phenotype. In addition, along with mutations, non-inherited changes are often found: phenocopies, terata, and morphoses. Therefore, the isolation of mutations begins in M2 (the second mutant generation), when at least part of the recessive mutations is manifested, and the likelihood of maintaining non-hereditary changes decreases. Typically, selection continues for 2–3 generations, although in some cases up to 5–7 generations are required to cull non-inherited changes (such non-hereditary changes that persist over several generations are called long-term modifications).
The obtained mutant forms either directly give rise to a new variety (for example, dwarf tomatoes with yellow or orange fruits) or are used in further breeding work.
However, the use of induced mutations in breeding is still limited, since mutations lead to the destruction of historically developed genetic complexes. In animals, mutations almost always lead to reduced viability or infertility. Therefore, in breeding, they try to use the already known mutations that have passed the test of natural selection.
Hereditary changes in a trait — a mutation — result from structural changes in genes or chromosomal rearrangements. Most of the changes that occur are harmful or useless. But some part of the mutations is useful for the breeder: non-invasive, immune forms appear, with cytoplasmic sterility, precocious, etc.
One of the advantages of the mutagenesis method over the hybridization method is the ability to obtain forms with completely new valuable traits that were not previously available in this crop, for example, with a sharply changed chemical composition (sunflower variety Pervenets).