How is corn bred? Understanding corn breeding methods in one article
How is corn bred? Please explain corn's natural cross-pollination habit and the heterozygosity of its genetic basis, as well as the breeding procedure that exploits the heterosis of F1 generations between inbred lines arising from this, which together form the particularity of corn breeding. With almost no exception, every successful corn breeder and research institute starts from...
How is corn bred? Please explain
Corn's natural cross-pollination habit and the heterozygosity of its genetic basis, together with the breeding procedure that exploits the heterosis of F1 generations between inbred lines arising from this, form the particularity of corn breeding. With almost no exception, every successful corn breeder and research institute starts by isolating a large number of inbred lines from abundant original materials or germplasm banks, then assembling a large number of hybrid combinations for testing, and finally selecting only a few outstanding hybrids for production use. This is because the probability of an excellent inbred line and an outstanding hybrid combination appearing is extremely low. When 1 locus is heterozygous, the frequency of dominant homozygotes and recessive homozygotes appearing in the selfed progeny is 1/4; when there are n loci, the frequency of individuals in the selfed progeny that are homozygous at all loci is (1/4)n. In China, only just over 20 parental inbred lines are currently used to make large numbers of hybrids; the same is true in the United States, where only about 40 parental inbred lines can be used on a large scale. They are all screened out from an enormous number of ear rows. In the United States alone, Pioneer Hi-Bred Seed Company screens about 7,000 new lines each year and arranges identification of 15,000 hybrid combinations, planting about 450,000 plots at about 250 different locations. Through all these trials, 7 to 10 commercial hybrids can be proposed each year in a normal year. This shows the enormous workload of corn breeding. In summary, using abundant germplasm resources, isolating a large number of inbred lines, making a large number of hybrid combinations, and through careful identification and screening breeding a few excellent inbred lines and strongly heterotic hybrids is the common experience of corn breeding at home and abroad. It is unrealistic to expect to screen out excellent inbred lines and hybrids from a small number of materials.
Corn breeding is mainly based on the use of heterosis; it starts with breeding inbred lines and takes the breeding and use of single-cross hybrids as its main purpose. The standards for breeding inbred lines are high yield in their own reproduction, good quality, multiple resistance, density tolerance and excellent comprehensive traits. The breeding method for inbred lines is linked to the type of original material and the target traits of breeding
1. Second-cycle line breeding: using single-cross hybrids and some commercial hybrids as original materials, generally adopting the conventional second-cycle line breeding method;
2. Population improvement method: when using synthetic varieties or populations with a complex genetic basis as original materials to breed inbred lines, two methods can be adopted: one is to combine population improvement, isolating inbred lines while carrying out recurrent selection. The other is to isolate inbred lines directly by the second-cycle line breeding method;
3. Backcross improvement and directed multiple-cross synthesis; these are effective ways to improve certain shortcomings of inbred lines;
4. Haploid breeding: including anther culture, androgenesis and gynogenesis methods;
5. Mutation breeding: using radiation to treat corn seeds, pollen and seedlings so as to produce variation;
6. Gamete selection method and the grain-storage improvement method: the former has been used rather rarely because its procedure is cumbersome, and the latter because of its limitations.
7. Biological breeding technology: since the 1980s, and especially in the mid-1990s, molecular biotechnology has been widely applied in corn breeding. Molecular marker technology has already been widely used in corn genetics and breeding research. Under certain conditions, it can accelerate the corn breeding process and improve selection effectiveness; used in research on genetic diversity, it can identify the diversity and differences of corn germplasm; used in research on QTLs, it can reveal the gene locus effects and effects of corn yield traits and quality traits controlled by multiple genes, and help understand the mechanism of heterosis; used in gene mapping, it can carry out gene cloning to produce precise corn gene maps, and may ultimately decipher all of corn's genetic code and regulate the inheritance of corn traits. As molecular biotechnology continues to improve and perfect, it will certainly be used even more widely in corn genetics and breeding research, promoting innovation and development in this discipline.
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