2.1 Genetic Similarity
The results of genetic similarity coefficient analysis of the tested materials were listed in Table 2, which varied from 0.4568 to 0.9974. The materials with the lowest similarity were C30 and C19, and the materials with the highest similarity were C16 and C18. The combinations with genetic similarity coefficients between 0.45 and 0.6 accounted for 68.81%, and the combinations between 0.60 and 0.75 accounted for 23.65%. The genetic similarity between varieties with the same parental origin was higher, and genetic similarity analysis provided a direct basis for material classification.
2.2 Population genetic structure
Population genetic structure refers to a non-random distribution of genetic variation in a species or population. The analysis of population structure helps to understand the evolution process, and the subgroup to which an individual belongs can be determined by the correlation study of genotype and phenotype. The results of genetic structure analysis of the tested material population are shown in Fig. 1. The test material C10 belongs to the REID group represented by pink; The ZI330 (ZI330 and Luda Honggu blood relationship) group represented by green had no test materials; Material C17 belongs to LAN(Lancaster) group represented by light blue; Since there is no reference inbred line in the blue classification, it is classified as an unknown group and there are 25 test materials.
2.3 Principal component analysis
In order to reflect the genetic relationship between different populations, PCA analysis was performed on the groups of tested materials based on SNP markers, and the material clustering was displayed in the form of graphs. The linear distance between materials in PCA was proportional to the genetic distance. Fig. 2 is a plan view of the PCA analysis of 30 test materials, and Fig. 3 is a three-dimensional view of the PCA analysis. The genetic materials of different subgroups in the PCA analysis are marked with different colors. According to the concentration degree of each material, samples C09 and C10 were divided into LAN population and REID population respectively, and samples C17, C26 and C30 were divided into SPT (Tang-Si-Ping-Tou) population. The other materials could not gather together effectively with the existing common corn group materials, so waxy corn materials should be classified separately.
2.4 Cluster analysis
Based on the results of genetic similarity test and the test data of representative materials for common maize group classification, 30 samples were mapped with specific representative materials from PB, SPT, REID, ZI330, 335FM(335 male parent blood relationship) and LAN populations, and the results were shown in Fig. 4. Among the 30 materials, 8 materials could be effectively integrated into the classification of common maize group, and 22 materials were clustered together independently, which was consistent with the results of principal component analysis.
In order to clarify the genetic relationship between waxy corn inbred lines and improve their utilization efficiency, a separate cluster analysis was performed on the tested waxy corn materials (Fig. 5). The 30 waxy corn materials can be roughly divided into five major groups, namely, Hengbai, YA, YB, YW and tropical material groups. C11, C15, C21, C23 and C25 belong to Hengbai group; C01, C02, C04, C08, C12, C20, C22 and C24 belong to YW group; C03, C17, C26 and C30 belong to YA group; C05, C09 and C10 belong to YB group; C06, C07, C13, C14, C16, C18, C27, C28 and C29 belong to tropical material group, and C19 could not cluster in these five groups effectively.