2.1 Phenotypic analysis of yield and fibre quality traits
Table 1 lists the phenotypic analysis of 4 yield traits and 5 fibre quality traits in parents and 784 F2 crosses in 2 years. In 2019, all the 9 traits of the parents were better than those of 2018, except the elongation because the field management of 2019 was better than 2018. Boll weight, fibre length, uniformity, micronaire and fibre strength of F2 crosses in 2018 were superior to those of their parents in the same environment. In 2019, the averages of boll number, boll weight, lint yield, fibre length, uniformity, micronaire and elongation of F2 crosses were higher than those in the same environment parents. The boll weight, fibre length, uniformity and micronaires of F2 in2018 and 2019 were higher than those of their parents in the same environment. These results indicated that heterosis and genetic interaction effects such as genotype environmental interaction effects of these traits could be observed.
Table 2 shows the ratios of genetic component variance to phenotype variance and heritability of four yield traits and five fibre quality traits of two years. As can be seen from Table 2, the additive effects of the other 7 traits reached extremely significant levels, except for the strength and micronaire values, which were 0. The additive effect of cloth parting was the largest, which was 43%. Fibre length comes in second at 39%. In the dominant effect pairs, except boll number per plant and elongation 0, the dominant effect of the other six characters reached extremely significant levels. Among them, garment part and strength had the largest dominant effect. The additive × environmental interaction effects were significant except for the uniformity. The dominant × environmental interaction of lint percentage and uniformity reached a very significant level. The interaction generalised heritability of the nine traits reached an extremely significant level, among which the interaction generalised heritability of the uniformity and elongation was the highest (22%) and the interaction generalised heritability of the lint percentage the lowest (8%).
2.2 Analysis of genetic effects of yield and fibre traits for parents
2.2.1 Additive effect analysis of parents
The genetic effects of yield and fibre quality traits were analysed to understand the application value of each parent's yield and fibre quality traits. Table 3 provides the estimates of the additive effects of seven major traits in 18 of 278 tested parents form Table S3 randomly. As can be seen from Table 3, the fibre length, uniformity and elongation of 223-28 and h288 had significant positive or extremely significant additive effects, and obtaining an offspring with high quality traits was easier if they were used as parents. Parents L17had a high positive additive effect in length (1.41 mm**) boll number (0.10**), lint yield(0.30**) and uniformity (1.41**)which could be used to improve fibre length, boll number, lint yield and uniformity of upland cotton progeny in the Alar area. 246-12 (0.81%+) had a significant additive effect in lint percentage and could be used as a parent to improve the offspring's lint percentage.
2.2.2 Dominance effect analysis of parents
Table 4 lists the estimates of the dominance effects of seven major traits in 24 of 278 tested parents from Table S4. As can be seen from Table 4, parent 267-7 had significant dominant effects on other traits except boll weight, lint percentage and strength. The results showed that the progenies crossed with this parent had better heterosis in lint yield, fibre length, uniformity and specific strength.
2.2.3 Analysis of the dominance effects of traits in F2 of some tested hybrid crosses
Table 5 lists the dominance effect values of 7 main characters in 10 crosses randomly. As can be seen from Table 5, the lint yield and uniformity of 267-7 × Ekangmian 2 had significant positive dominance effects, which was due to the high negative dominance effects of these two traits in both parents. The crosses 223-28 × 246-12 had higher dominance effect on lint percentage.
2.2.4 Analysis of additive × environmental interaction of some parents
Table 6 lists the additive × environmental interaction values of 9 traits in some parents randomly. Parent Xinluzao 66 showed significant positive additive × environmental interaction effect in lint percentage 2 years, indicating that parent Xinluzao 66 had different effects on this trait in different environments. Combining the two years' performance, the additive × environmental interaction effect of parents in 2019 was higher than that in 2018, which might be because the environmental conditions in 2019 were better than those in 2018. The nine traits of other parents had significantly different dominant × environmental interaction effects in different years.
2.2.5 Analysis of dominance × environmental interaction of some crosses
Table 7 lists the effect values of four traits with significant dominance × environmental interaction in some crosses randomly. The lint yield per plant of Xinluzao 30 × Liumian 2 in two years showed significant positive dominant × environmental interaction effect, indicating that the lint yield per plant of these combinations might show positive heterosis in different years, but significant negative dominant × environmental interaction effect existed in uniformity in 2018. In 2019, however, a positive dominant × environmental interaction effect occurred, indicating that this combination showed significant differences in different years.
2.3 Genetic clustering of parental genetic effects
2.3.1 Genetic clustering of additive effects of parents
Clustering the genetic main effect of multiple varieties (lines) can determine the utilisation path of different parents. The additive effect and additive × additive epistasis effect of parents are primarily used in cross breeding. By analysing the additive effect of parents, the advantages and disadvantages of parents in different traits can be known, and then the parents can be selected for pertinence. The number of clustering of additive effects of multiple traits of multiple parents can be determined by using a gravel map, and the utilisation value of different parents in cross breeding can be determined by clustering. Figure 2 and 3 show the results of clustering the additive effects of 7 traits in 278 varieties (lines). As can be seen from Figure 3 and Table 8, 13 materials (222-13, 223-14, 1048, etc.) in group 5 had high additive effect on fibre length (3.20 mm), uniformity (2.77%) and elongation (1.25%). Therefore, Obtaining good quality traits of the offspring is easy in this kind of variety (line) when selecting the parents of distant hybridisation. The tenth group included 24 varieties (zh3-14, Xinluzhong 37, L14-4 etc.), which had higher additive effect on boll number (0.41 ), boll weight (1.14 g), lint percentage (0.68%) and lint yield per plant (1.15 g). Therefore, through the cross between these varieties (lines), the offspring of these varieties (lines) can be obtained with higher yield traits. Combined with the average value of 7 main traits, the fourth group was higher. The progeny with both yield and quality traits could be obtained by crossing among these varieties (lines).
Table 9 shows the additive effect clustering of other varieties.
2.3.2 Genetic clustering of parental dominance effects
The dominance effects of seven main traits in 278 varieties (lines) were grouped and clustered as shown in Figure 4 and 5. As can be seen from Figure 4 and Table 10, the first group, including 13 materials (Xinluzhong 37, Zhongzi 10, 223-6, etc.), had higher dominance effects in boll weight (-1.04g), lint percentage (-0.82%) and lint yield per plant (-0.97g). Therefore, obtaining higher heterosis is possible for these traits in the offspring of these varieties (lines) by crossing them. In the twelfth group, 22 materials (15-1990-7, Xiangmian 16, Han 4849, etc.) had high dominance effect on four fibre quality traits. Additionally, heterosis with higher length, uniformity, microneron value and strength was easily obtained by crossing these parents.
Table 11 shows the clustering of dominance effects of other varieties.
2.4 Decision-making coefficient analysis on main traits in F2
2.4.1 Decision-making coefficients of genetic components on other traits to lint yield
Table 12 lists the decision-making coefficients of various traits on lint yield. The additive decision-making coefficients and dominance ×environment are all 0. The results showed that the additive effects and dominance ×environment of other traits did not determine or restrict lint yield. The order of the positive decision-making coefficient of the dominance effects was lint percentage [R (i)2= 0.025] and fibre length [R (i)2= 0.008] . Thus, the decision-making traits that affected the dominance effects of lint yield were lint percentage and fibre length. The order of the negative decision-making coefficient of dominance effects on lint yield was strength [R (i)2= -0.002]. The results showed that high lint percentage and low fibre length selected to exhibit the dominance effects could enhance lint yield. For additive × environment, the additive × environmental interaction decision-making coefficients of each traits were negative except for strength and boll weight, indicating that the dominance × environmental effects of uniformity and elongation were the restricting factors for crosses with high lint yield in different environments. The phenotypic decision-making coefficient of each trait on lint yield was the highest with boll number [R (i)2= 0.002], indicating that boll number was the main decision-making traits in improving lint yield phenotypic value.
2.4.2 Decision-making coefficients of genetic components on other traits to length
Table 13 lists the decision-making coefficients of various traits on length. The order of the positive decision-making coefficient of the additive decision-making coefficients, dominance decision-making coefficients, additive × environment decision-making coefficients, dominance × environment and genotype decision-making coefficients was lint percentage. The results showed that choosing parents with high lint percentage could improve the length of hybrid. For additive × environment interaction effects, the order of the negative decision-making coefficient were boll number/plant [R (i)2= -0.126], micronaire [R (i)2= -0.022] and strength [R (i)2= -0.022]. Thus, the main restricting trait was boll number/plant in a specific environment. The main decision-making traits of the phenotype value of length were uniformity [R (i)2= 0.001] and strength [R (i)2= 0.001]. These results showed that the increase in phenotype values of uniformity and strength could increase the phenotype values of length. The main positive decision-making coefficients of length were lint percentage [R (i)2= 0.002] and uniformity [R (i)2= 0.001], suggesting that the in the two genotype values could improve the genotype values of length.
2.4.3 Decision-making coefficients of genetic components on other traits to micronaire
Table 14 lists the decision-making coefficients of various traits on micronaire. The additive decision-making coefficients of micronaire, phenotype and genotype were 0, and were thus not discussed. For dominance decision-making coefficients of micronaire, the order of positive was lint percentage [R (i)2= 0.013], fibre length [R (i)2= 0.009]. Therefore, the crosses with low dominance effect of lint percentage and fibre length are more beneficial to reduce the micronaire of hybrids. The additive×environmental interaction decision-making coefficient [R (i)2= 0.005] and dominance×environmental interaction decision-making coefficient [R (i)2= 0.003] of each trait on micronaire indicated that fibre strength was the restricting factor for better crosses of micronaire in different environments.
2.4.4 Decision-making coefficients of genetic components on other traits to strength
Table 15 lists the decision-making coefficients of various traits on micronaire. The additive decision-making coefficients of micronaire, phenotype and genotype were 0, showing that the additive effects of other traits do not determine or restrict the increasing strength. The dominance decision-making coefficient is the largest by length [R (i)2= 0.032], followed by the length [R (i)2= 0.030]and the smallest length [R (i)2= -0.003]. Therefore, the decision-making trait that uses the dominance effect to improve the fibre strength is the length and fibre length, and the main restricting trait is cotton yield. The crosses of high dominance effect of fibre length is more beneficial to improve the strength of hybrids. The main decision-making traits of the additive×environment value of strength was micronaire [R (i)2= 0.005]. In different environments, the additive of micronaire × environmental effect is the decisive factor for the crosses of high strength. The length of dominance × environmental decision-making coefficient of each character was [R (i)2= -0.003], which indicated that dominance × environmental interaction effect of length had restricted effect on dominance × environmental interaction effect of intensity.