Maize Genomics and Genetics 2025, Vol.16, No.1, 45-59 http://cropscipublisher.com/index.php/mgg 48 plant and the number of grains per row are particularly sensitive to water and fertilizer conditions (Naggar et al., 2020). Therefore, when breeding, you can't just look at the variety, you also have to consider where it will be planted in the future. After all, the same corn planted in different plots may have a very different harvest. Corn hybridization is quite interesting. The "children" born from the same parents in different places may be very different. For example, some hybrid combinations grow particularly well in the north, with long and thick ears and full grains, but they may perform mediocrely in the south (Yu et al., 2020). This reminds breeding experts that they cannot only conduct research in the laboratory. Now they pay more and more attention to field testing, after all, corn will eventually be planted in the field. Some varieties look good in data, but when they are planted in fields with different climatic conditions, their performance may be completely different (Yu et al., 2020). Therefore, when breeding new varieties, environmental factors must be taken into account, so that good varieties with strong adaptability can be selected. 4 Genotypic Diversity of Maize 4.1 Sources of genetic variation in maize The genes of corn are like a hodgepodge, with a lot of variations - this has become its specialty in adapting to different environments. Where do these variations come from? Some are natural mutations, some are hybridization and recombination, and some are the result of artificial selection. Take Chinese summer corn for example. Although they are all from the same ecological zone, the genetic differences between different varieties are not small (Shu et al., 2020). Interestingly, these Chinese varieties are also mixed with a lot of North American corn genes. In the past 20 years, North American germplasm has made a significant contribution to the genetic improvement of Chinese summer corn (Shu et al., 2020). However, genetic variation is also very selective. The part of the corn chromosome close to the telomeres has a lot of variation, while the area close to the centromere is relatively conservative (Figure 1). This "selective" variation pattern makes breeding work more interesting. Figure 1 The molecular characteristics of maize genomes (Adopted from Shu et al., 2020) Image caption: (a) Minor allele frequency distribution; (b) Physical distance between adjacent SNP loci; (c) LD pattern of SNP loci along each of the 10 chromosomes; (d) The Relative kinship of 490 inbreds (Adopted from Shu et al., 2020)
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