Stability Evaluation for Main Quality Traits of Soybean in the Northeast and Huang-Huai-Hai Regions

: The content of protein and oil in soybeans is an important trait for evaluating quality and is regulated by genetic and environmental factors, lacking comprehensive identification under a variety of ecological conditions. Therefore, evaluating the stability of soybean quality traits under different environmental conditions has great significance for various applications. In this study, we compare 150 soybean varieties from Northeast China (Group A and Group B) and the Huang-Huai-Hai region (Group C). As the release time progressed, the oil content in the soybean varieties showed an upward trend in both Northeast China and the Huang-Huai-Hai region, while the protein content showed a downward trend. Additionally, the oil contents were negatively correlated with the protein contents and the sum of protein and oil contents, while the protein contents were positively correlated with the sum of protein and oil contents, with the correlation becoming stronger as the latitude decreased. Moreover, there were obvious variations in quality stability among different varieties. Hefeng 45, Jilinxiaolidou 4, and Zhonghuang 19 had relatively high protein contents and exhibited good stability across different environments, while Kenjiandou 25, Changnong 17, Dongnong 46, Kennong 17, Liaodou 14, and GR8836 had relatively high oil contents with good stability performance in varying environments.


Introduction
Soybean (Glycine max (L.) Merr.), originating in China, stands as a pivotal oil crop and a vital source of plant-based protein for human consumption worldwide [1][2][3].The enhancement of protein and oil content is of growing importance.Soybean seeds boast a high concentration of fats and proteins, serving dual roles as a nutrient reservoir for the growth of seedlings and as a key raw material for the extraction of soy protein and oil in the food processing industry [4][5][6].Consequently, the improvement in soybean quality, particularly focusing on its protein and oil content, has garnered significant interest.Extensive research has revealed that soybean quality characteristics are influenced by both genetics and environmental factors [7][8][9][10].Soybean varieties in China's three major ecological regions-the North, Huang-Huai-Hai, and the South-exhibit a north-to-south gradient with increasing protein content and a corresponding decrease in oil content.Soybeans with a high level of crude protein content are mainly concentrated in the Yangtze River basin and the southwestern mountainous area, while soybeans rich in crude oil content are primarily distributed in the northeastern and northwestern regions of China [11].
Agronomy 2024, 14, 872 2 of 15 It has been suggested that the observed variations in fat accumulation are related to regional differences in environmental factors, such as temperature, precipitation, diurnal temperature variation, and sunlight exposure.As a result, the oil content in a single soybean variety may vary by over 1% due to differing meteorological conditions and cultivation practices across various locations [12].Drawing on data from 2005 to 2018, Wang et al. [13] performed a quality analysis of Neidou 4, the predominant soybean variety cultivated in Inner Mongolia's premier production area and found that temperature and precipitation were critical meteorological factors influencing the protein content and that temperature alone was the principal factor affecting oil content.The Northeast, which has abundant sunlight, significant diurnal temperature variations, and moderate rainfall and growth-period temperatures, stands out as an optimal region for cultivating high-oil soybean varieties [14,15].However, high-protein varieties thrive in the northern and central parts of China.The influence of latitude and terrain on soybean quality is the result and manifestation of the comprehensive effects of light, temperature, water, and nutrients [16].
The evaluation of soybean germplasm quality traits is often based on a single or a few experimental points [17,18], lacking comprehensive identification under a variety of ecological conditions; thus, exceptional resources of outstanding quality stability are seldom discovered.Nevertheless, identifying high-quality soybean germplasm that remains stable despite environmental variations is crucial for enhancing agricultural productivity, given that protein and oil contents are determined by genetic factors and modulated by the environment [19].Accounting for 79% of China's soybean cultivation area in 2023, the Northeast and Huang-Huai-Hai regions are increasingly important for soybean growth (data sources: https://data.stats.gov.cn/?luicode=10000011) [20].This study conducted multisite evaluations of germplasm from the Northeast and Huang-Huai-Hai regions, analyzing the mean values and stability of protein and oil content, with the aim of identifying outstanding germplasm with exceptional and stable quality traits to lay the material foundation for the cultivation of new high-oil, high-yield, and high-protein soybean varieties.

Experimental Material
This research utilized 150 soybean varieties from the Northeast and Huang-Huai-Hai regions as experimental materials (Table 1).These varieties were divided into three distinct geographic groups based on their growth locations.Groups A and B encompassed soybean varieties from the northern and central parts of the Northeast, respectively, and Group C comprised varieties from the Huang-Huai-Hai region.Each group notably consisted of an equal representation of 50 soybean varieties.

Analytical Methods
The varieties from the three regions were obtained from the Northeast and Huang-Huai-Hai regions in 2012.The trial sites for the varieties from the northern part of the Northeast (Group A) included Zhalantun (47   Each trial site followed a completely random experimental design, with a row len of 3 m.All trial sites maintained uniform management standards, applying 30 kg of co pound fertilizer/acre before sowing and an additional 10 kg/acre before flowering, ens ing sufficient moisture with all materials harvested at full maturity.The content of prot and oil was determined using a near-infrared particle analyzer (Bruker, Germany).S bean seed samples with clean surfaces, no cracks, no patches, and intact particles w selected.The spectral data of the samples were analyzed using OPUS 5.0 software, a the protein and oil content data were obtained by using a soybean protein and oil dry b model.Each material was measured three times and averaged to represent the prot and fat content of the sample [21].Both protein content and oil content, as well as the s of protein and oil contents, were expressed as percentages.
The GGE (genotype main effects and genotype × environment interaction) biplot method used to evaluate the interaction effects of germplasm (G) with the environm (E) [22,23].In this study, the evaluation of the quality traits and stability of soyb germplasm at different trial sites in regions A, B, and C was performed through a G model using the R package (v4.3.1)GGEBiplotGUI.The specific parameters were as lows: Biplot tools = Rank genotypes with reference to the ideal genotype, Centered b tester-centered G + GE, Scaled = no scaling, SVP = JK.Pearson correlation coefficient an ysis was conducted to test the relationship between protein content and oil content in ferent ecological regions.T-tests were employed to verify statistical significance.Statist analyses were performed using R (v4.3.1).
Figure 1.Distribution of experimental sites within the three regions.Three regions (Group A, Group B, and Group C) were set with 4, 5, and 6 experimental sites, respectively.The orange circles represent the distribution of experimental sites of Group A, with A1-A4 representing Zhalantun, Heihe, Jiusan Farm, and Yaergenchu, respectively.The green circles represent the distribution of experimental sites in Group B, with B1-B5 being Jiamusi, Suihua, Gongzhuling, Tonghua, and Yanbian, respectively.The purple circles represent the distribution of experimental sites in Group C, with C1-C6 being Shijiazhuang, Handan, Zhoukou, Fuyang, Bengbu, and Bozhou, respectively.
Each trial site followed a completely random experimental design, with a row length of 3 m.All trial sites maintained uniform management standards, applying 30 kg of compound fertilizer/acre before sowing and an additional 10 kg/acre before flowering, ensuring sufficient moisture with all materials harvested at full maturity.The content of protein and oil was determined using a near-infrared particle analyzer (Bruker, Germany).Soybean seed samples with clean surfaces, no cracks, no patches, and intact particles were selected.The spectral data of the samples were analyzed using OPUS 5.0 software, and the protein and oil content data were obtained by using a soybean protein and oil dry base model.Each material was measured three times and averaged to represent the protein and fat content of the sample [21].Both protein content and oil content, as well as the sum of protein and oil contents, were expressed as percentages.
The GGE (genotype main effects and genotype × environment interaction) biplot is a method used to evaluate the interaction effects of germplasm (G) with the environment (E) [22,23].In this study, the evaluation of the quality traits and stability of soybean germplasm at different trial sites in regions A, B, and C was performed through a GGE model using the R package (v4.3.1)GGEBiplotGUI.The specific parameters were as follows: Biplot tools = Rank genotypes with reference to the ideal genotype, Centered by = testercentered G + GE, Scaled = no scaling, SVP = JK.Pearson correlation coefficient analysis was conducted to test the relationship between protein content and oil content in different ecological regions.T-tests were employed to verify statistical significance.Statistical analyses were performed using R (v4.3.1).

Comparison of Quality Traits in Soybean Germplasms across Different Decades
To explore the quality characteristics of the varieties bred at different stages, comparisons of the protein content, oil content, and sum of protein and oil contents were made for varieties developed in different decades.Soybean germplasms from the three geographic areas were sorted into three chronological categories according to their year of official release: those released before 1990, those released between 1990 and 2000, and those released after 2000.In the three regions, the overall protein content tended to decline with the certification time of the variety (Figure 2A), with Group A showing a trend of first decreasing and then increasing and Group B showing a trend of decreasing, followed by a slow recovery.The protein content decline in Group C was the most significant.Conversely, the oil content generally showed an increasing trend over the certification years in all three regions (Figure 2B).The sum of protein and oil showed a continuous downward trend in Groups B and C, with a relatively slow decline in Group B. In Group A, it showed a trend of initial decline, followed by an increase.This means that the sum of protein and oil of the germplasm certified between 1990 and 2000 was less than that of the germplasm certified after 2000, which were both less than that of the germplasm certified before 1990 (Figure 2C).The above analysis indicates that, in recent years, the overall oil content of soybean germplasm in various regions has shown an upward trend, while the protein content has generally shown a downward trend.

Comparison of Quality Traits in Soybean Germplasms across Different Decades
To explore the quality characteristics of the varieties bred at different stages, comparisons of the protein content, oil content, and sum of protein and oil contents were made for varieties developed in different decades.Soybean germplasms from the three geographic areas were sorted into three chronological categories according to their year of official release: those released before 1990, those released between 1990 and 2000, and those released after 2000.In the three regions, the overall protein content tended to decline with the certification time of the variety (Figure 2A), with Group A showing a trend of first decreasing and then increasing and Group B showing a trend of decreasing, followed by a slow recovery.The protein content decline in Group C was the most significant.Conversely, the oil content generally showed an increasing trend over the certification years in all three regions (Figure 2B).The sum of protein and oil showed a continuous downward trend in Groups B and C, with a relatively slow decline in Group B. In Group A, it showed a trend of initial decline, followed by an increase.This means that the sum of protein and oil of the germplasm certified between 1990 and 2000 was less than that of the germplasm certified after 2000, which were both less than that of the germplasm certified before 1990 (Figure 2C).The above analysis indicates that, in recent years, the overall oil content of soybean germplasm in various regions has shown an upward trend, while the protein content has generally shown a downward trend.

Correlation Analysis of Quality Traits among Different Regions
A correlation analysis was conducted on the protein content, oil content, and sum of protein and oil of soybean germplasms from different regions.The oil content was negatively correlated with both the protein content and the sum of protein and oil; the correlation coefficients were −0.76, −0.82, −0.93, −0.25, −0.48 and −0.77, with the negative correlation being strongest in Group C (−0.93, −0.77) and weakest in Group A (−0.76, −0.25) (Table 2).The protein content and the sum of protein and oil were positively correlated in all three regions, with the correlation strength decreasing from Group C (0.95) to Group B (0.9) and then to Group A (0.82) (Table 2).The analysis suggests that an increase in oil content often coincides with a decrease in protein content and in the sum of protein and oil contents.Conversely, there is a positive relationship between protein content and the sum of protein and oil contents that which strengthens as latitude decreases.

Correlation Analysis of Quality Traits among Different Regions
A correlation analysis was conducted on the protein content, oil content, and sum of protein and oil of soybean germplasms from different regions.The oil content was negatively correlated with both the protein content and the sum of protein and oil; the correlation coefficients were −0.76, −0.82, −0.93, −0.25, −0.48 and −0.77, with the negative correlation being strongest in Group C (−0.93, −0.77) and weakest in Group A (−0.76, −0.25) (Table 2).The protein content and the sum of protein and oil were positively correlated in all three regions, with the correlation strength decreasing from Group C (0.95) to Group B (0.9) and then to Group A (0.82) (Table 2).The analysis suggests that an increase in oil content often coincides with a decrease in protein content and in the sum of protein and oil contents.Conversely, there is a positive relationship between protein content and the sum of protein and oil contents that which strengthens as latitude decreases.

Correlation Coefficient Significance
The protein and oil contents in Group A −0.76 The protein content and sum of protein and oil in Group A 0.82 0 The protein content and sum of protein and oil in Group B 0.9 0 The protein content and sum of protein and oil in Group C 0.95 0

Analysis of Soybean Germplasm Quality Traits in Three Regions
Upon examining the protein and oil content and the combined protein-oil content in soybean germplasm samples from three geographical regions, discernable variations in the quality features among these regions were detected.The mean protein levels for the germplasm from Groups A, B, and C were 39.00, 38.98, and 40.11%, respectively (Figure 3A).Groups A and B exhibited comparable protein levels, whereas Group C exhibited a noteworthy increase in protein content when juxtaposed with Groups A and B (Figure 3A).Regarding oil content, germplasm from Groups A, B, and C had average percentages of 20.74, 21.34, and 21.45%, respectively (Figure 3B).There was an absence of a significant disparity between the oil content present in Groups B and C; however, both demonstrated significantly greater values than Group A (Figure 3B).The sum of protein and oil contents among the germplasm groups was in the following order from lowest to highest: Groups A, B, and C (Figure 3C).Collectively, the protein content, oil content, and sum of protein and oil contents in Group C were higher than those in Groups A and B, with the protein content and the sum of protein and oil contents of Group C being particularly notable.The protein content and sum of protein and oil in Group A 0.82 0 The protein content and sum of protein and oil in Group B 0.9 0 The protein content and sum of protein and oil in Group C 0.95 0

Analysis of Soybean Germplasm Quality Traits in Three Regions
Upon examining the protein and oil content and the combined protein-oil content in soybean germplasm samples from three geographical regions, discernable variations in the quality features among these regions were detected.The mean protein levels for the germplasm from Groups A, B, and C were 39.00, 38.98, and 40.11%, respectively (Figure 3A).Groups A and B exhibited comparable protein levels, whereas Group C exhibited a noteworthy increase in protein content when juxtaposed with Groups A and B (Figure 3A).Regarding oil content, germplasm from Groups A, B, and C had average percentages of 20.74, 21.34, and 21.45%, respectively (Figure 3B).There was an absence of a significant disparity between the oil content present in Groups B and C; however, both demonstrated significantly greater values than Group A (Figure 3B).The sum of protein and oil contents among the germplasm groups was in the following order from lowest to highest: Groups A, B, and C (Figure 3C).Collectively, the protein content, oil content, and sum of protein and oil contents in Group C were higher than those in Groups A and B, with the protein content and the sum of protein and oil contents of Group C being particularly notable.An analysis of the range of variation in quality traits of germplasm from different regions was also conducted.This evaluation included the measurement of the coefficient of variation (CV) for protein content within each germplasm group.Specifically, Groups A, B, and C showcased CVs of 0.035, 0.040, and 0.063, respectively, culminating in a mean CV of 0.046.The oil content featured CVs of 0.041, 0.037, and 0.065, with an overall average CV of 0.048.When considering the aggregate sum of protein and oil, the CVs were 0.017 for Group A, 0.015 for Group B, and 0.022 for Group C, with an average CV of 0.018 (Table 3).The CVs for protein content, oil content, and the sum of protein and oil were the highest An analysis of the range of variation in quality traits of germplasm from different regions was also conducted.This evaluation included the measurement of the coefficient of variation (CV) for protein content within each germplasm group.Specifically, Groups A, B, and C showcased CVs of 0.035, 0.040, and 0.063, respectively, culminating in a mean CV of 0.046.The oil content featured CVs of 0.041, 0.037, and 0.065, with an overall average CV of 0.048.When considering the aggregate sum of protein and oil, the CVs were 0.017 for Group A, 0.015 for Group B, and 0.022 for Group C, with an average CV of 0.018 (Table 3).The CVs for protein content, oil content, and the sum of protein and oil were the highest in Group C. In addition, the range of variation in protein and oil content in the germplasm of Group C was larger than that of Groups A and B (Table 3).These results suggest a greater variation in quality traits among different germplasms in Group C. Different lowercase letters (a, b, and c) indicate significant differences and identical letters suggest insignificant differences in one-way analysis of variance (ANOVA).

Stability Analysis of Quality Traits in Soybean Germplasms from Three Regions
In the pursuit of identifying germplasms that exemplify superior quality attributes alongside robust stability, a comparative analysis was conducted.This analysis assessed the average content alongside the variability of protein and oil content, as well as the cumulative protein and oil content, among various resources from multiple regions across distinct localities.
Within Group A, Mengdou 11 stood out, boasting the highest average protein content of 43%.The mains varieties with oil content greater than or equal to 22% were Hefeng 42, Kenjianbean 25, Suinong 11, and Fengshou 18. Hefeng 30 was distinguished by its remarkable stability regarding protein content, with a minimal CV of 1.12%.Hefeng 45 demonstrated an impressive blend of richness and relative stability in protein content, marked by a CV of 2.36% (Figure 4).In terms of oil content, Hefeng 42 was the frontrunner in the region, with an average of 22.9%, whereas Kenfeng 11 showcased remarkable consistency in oil content, evidenced by its low CV of 0.68%.Kenjiandou 25 also featured a noteworthy combination of high and relatively constant oil content (Figure 4).Mengdou 11 had the highest combined protein and oil content in the region, achieving a total of 62%.Considering stability, Suinong 18 emerged as the most reliable, with a CV of 0.46%.Beifeng 11 had a high and relatively stable sum of protein and oil contents (Figure 4, Table 4).
Agronomy 2024, 14, x FOR PEER REVIEW 7 of 15 in Group C. In addition, the range of variation in protein and oil content in the germplasm of Group C was larger than that of Groups A and B (Table 3).These results suggest a greater variation in quality traits among different germplasms in Group C. Different lowercase letters (a, b, and c) indicate significant differences and identical letters suggest insignificant differences in one-way analysis of variance (ANOVA).

Stability Analysis of Quality Traits in Soybean Germplasms from Three Regions
In the pursuit of identifying germplasms that exemplify superior quality attributes alongside robust stability, a comparative analysis was conducted.This analysis assessed the average content alongside the variability of protein and oil content, as well as the cumulative protein and oil content, among various resources from multiple regions across distinct localities.
Within Group A, Mengdou 11 stood out, boasting the highest average protein content of 43%.The mains varieties with oil content greater than or equal to 22% were Hefeng 42, Kenjianbean 25, Suinong 11, and Fengshou 18. Hefeng 30 was distinguished by its remarkable stability regarding protein content, with a minimal CV of 1.12%.Hefeng 45 demonstrated an impressive blend of richness and relative stability in protein content, marked by a CV of 2.36% (Figure 4).In terms of oil content, Hefeng 42 was the frontrunner in the region, with an average of 22.9%, whereas Kenfeng 11 showcased remarkable consistency in oil content, evidenced by its low CV of 0.68%.Kenjiandou 25 also featured a noteworthy combination of high and relatively constant oil content (Figure 4).Mengdou 11 had the highest combined protein and oil content in the region, achieving a total of 62%.Considering stability, Suinong 18 emerged as the most reliable, with a CV of 0.46%.Beifeng 11 had a high and relatively stable sum of protein and oil contents (Figure 4, Table 4).
(A) (B) (C)   In Group B, KatoProto had the highest protein content, with an average of 42.90%.Heihe 28 exhibited notable stability in this indicator, with a coefficient of variation (CV) of only 1.13%.Additionally, Jilinxiaolidou 4 had a protein content of 40.6% with a low degree of variation (Figure 5).Changnong 17 exhibited the highest oil content within its region, averaging 23.10%, and was characterized by a modest CV of 2.35%.Except for Suinong 21, Jiufeng 4, Jilinxiaolidou 4, Heihe 28, Heinong 48, Suinong 15, and Jiyuan Yin 3, the oil contents were equal to or greater than 22%.Changnong 17, Dongnong 46, and Kenfeng 17 had significant oil contents with low variation.Suinong 21, in particular, had the smallest CV for oil content, at 1.38%.KatoProto recorded the highest cumulative protein and oil content in the region, which reached 62.6%.In terms of consistency, Jilin 47 maintained a low CV of 0.78% (Table 5).
germplasm; (C) the sum of protein and oil contents and the coefficient of variation of the germplasm.Standard deviation (SD).In Group B, KatoProto had the highest protein content, with an average of 42.90%.Heihe 28 exhibited notable stability in this indicator, with a coefficient of variation (CV) of only 1.13%.Additionally, Jilinxiaolidou 4 had a protein content of 40.6% with a low degree of variation (Figure 5).Changnong 17 exhibited the highest oil content within its region, averaging 23.10%, and was characterized by a modest CV of 2.35%.Except for Suinong 21, Jiufeng 4, Jilinxiaolidou 4, Heihe 28, Heinong 48, Suinong 15, and Jiyuan Yin 3, the oil contents were equal to or greater than 22%.Changnong 17, Dongnong 46, and Kenfeng 17 had significant oil contents with low variation.Suinong 21, in particular, had the smallest CV for oil content, at 1.38%.KatoProto recorded the highest cumulative protein and oil content in the region, which reached 62.6%.In terms of consistency, Jilin 47 maintained a low CV of 0.78% (Table 5).Group C's Shuilizhan, Yudou 12, and Yangyanjingdou had more than 45% protein content, with Shuili Station having the highest protein content of 46.9%.The protein content of Liaoshou 2 remained stable, with a coefficient of variation (CV) of 3.69%.Zhonghuang 19 had a high protein content of 42%, on average, and a low CV of 5.19% (Figure 6).Zhonghuang 20 had the highest oil content in the region, with an average of 24%, while Dongdou 1 was the most stable, with a CV of just 2.48%.Liaodou 14 and GR8836 exhibited high and comparatively steady oil contents (Figure 6).Except for Dongdou 1, Ludou 8, Liaoshou 2, Tiefeng 31, and Qingpipingdingxiang, the oil contents were more than 22%.Yudou 12 had the highest sum of protein and oil in the region, reaching 64.60%, and Yudou 19 had the most stable sum of protein and oil, with a CV of 0.94% (Figure 6, Table 6).Group C's Shuilizhan, Yudou 12, and Yangyanjingdou had more than 45% protein content, with Shuili Station having the highest protein content of 46.9%.The protein content of Liaoshou 2 remained stable, with a coefficient of variation (CV) of 3.69%.Zhonghuang 19 had a high protein content of 42%, on average, and a low CV of 5.19% (Figure 6).Zhonghuang 20 had the highest oil content in the region, with an average of 24%, while Dongdou 1 was the most stable, with a CV of just 2.48%.Liaodou 14 and GR8836 exhibited high and comparatively steady oil contents (Figure 6).Except for Dongdou 1, Ludou 8, Liaoshou 2, Tiefeng 31, and Qingpipingdingxiang, the oil contents were more than 22%.Yudou 12 had the highest sum of protein and oil in the region, reaching 64.60%, and Yudou 19 had the most stable sum of protein and oil, with a CV of 0.94% (Figure 6, Table 6).

Discussion
Soybean is one of the most widely cultivated crops in the world, and its protein and oil account for 69% and 30% of human and livestock consumption, respectively [24,25].As a major source of plant fat and protein, modern cultivated soybean seeds contain about 17% oil and 35% protein (including essential and non-essential amino acids) [26].In China, the Northeast and Huang-Huai-Hai regions account for approximately 64% and 15% of the total soybean planting area, respectively (data sources: https://data.stats.gov.cn/?luicode= 10000011) [20], making them the main soybean-producing regions.Protein content and oil content are the most important quality indicators for soybeans, but they are easily influenced by the environment.This study compared the variability in protein and oil content among 150 varieties across multiple locations in the Northeast and Huang-Huai-Hai regions.It also evaluated the quality traits and stability of these varieties using the mean, CV, and GGE biplot models, among other methods.

Excellent Quality Traits of Varieties
Soybean quality traits are significantly influenced by the combined effects of genotype and environment [27][28][29][30], and the interaction between genotype and environment notably affects soybean protein and amino acid concentrations.However, the variations in soybean protein and amino acid content are dominated by genotype and environment rather than by the interaction between them [31,32].For example, each soybean genotype was planted in four locations in Manitoba during 2018 and 2019, genotypes and environments exhibited the largest variation for protein and amino acid contents in soybeans [29].This study analyzed 150 varieties from the perspectives of the mean value and stability of multiple location quality measurement values, selecting germplasm with higher mean values and better stability of quality traits within different planting areas, some of which are of high quality and relatively stable.For example, HeFeng 45 from Group A in the northern portion of the Northeast, Jilinxiaolidou 4 from Group B in the central portion of the Northeast, and Zhonghuang 19 from the Huang-Huai-Hai region performed better in terms of protein content with an average value that was greater than 40% and these areas were also better in terms of stability.Meanwhile, Kenjiandou 25 from Group A, Changnong 17, Dongnong 46, and Kennong 17 from Group B in the Northeast region, and Liaodou 14 and GR8836 from the Huang-Huai-Hai region were greater than 22% that were more stable in the environment.The above materials can serve as parental lines for quality improvement breeding programs, providing clues for the development of new varieties with good quality and stability through hybrid convergence breeding.

Changes in Soybean Variety Quality Traits in the Huang-Huai-Hai and Northeast Regions during Different Periods
The economic and nutritional value of soybeans is determined by their seed protein and oil content [33].To understand the impact of the breeding process on quality traits, this study compared the quality trait changes of varieties bred during different periods.Varieties bred in the 1980s and earlier exhibited a lower oil content and a higher protein content compared to those bred after the 1990s.Over time, the protein content generally showed a decreasing trend, while the oil content increased, indicating that soybean breeding in recent years has primarily focused on increasing the oil content [34,35].However, it is important to note that with genetic improvement, both the protein content and the combined protein and oil content decreased [36].Since domestic soybeans are mainly used for consumption, subsequent soybean genetic improvements should focus on increasing the protein content and gradually increasing yield levels.
Protein content and oil content are the main quality traits of soybean seeds, determined by quantitative loci and their interaction with the environment [37].Prenger, based on 2017 yield trial data, found significant negative relationships between protein and yield and between protein and oil [38].The analysis of soybean protein and oil content was conducted on 292 soybean materials, revealing that these two traits exhibited a normal distribution within natural populations and were widely mutated within the population and showed a negative correlation [39].Comparing the protein content among varieties from different regions showed that the protein content of varieties in the Huang-Huai-Hai region has always been higher than that of varieties in the Northeast region.Among varieties bred before the 1990s, the oil content of varieties in the Huang-Huai-Hai region was significantly lower than that of varieties in the Northeast region.For varieties bred after the 1990s, the oil content of varieties in the Huang-Huai-Hai region increased significantly, and their overall oil content was higher than that of varieties in the Northeast region.Relative to the Northeast region, the protein and oil content in the Huang-Huai-Hai region was maintained at a higher level.Considering both protein content and oil contents, the sum of protein and oil showed a downward trend due to the decrease in the protein contents of varieties in different regions, but the sum of protein and oil of varieties in the Huang-Huai-Hai region had always been higher than that in the Northeast region.Therefore, in terms of quality traits, the Huang-Huai-Hai region maintained higher levels of protein and oil content, making it suitable for the production of high-quality soybeans.Additionally, the range of variation in protein and oil content among varieties in the Huang-Huai-Hai region was wide, and there was a strong negative correlation between protein and oil content, which is conducive to breeding varieties with specific uses for protein or oil.
In summary, this study evaluated the quality traits of 150 soybean varieties from the Huang-Huai-Hai and Northeast regions across multiple locations, revealed patterns of quality variation among regional varieties, identified excellent varieties of resources with good quality traits and stability, and provided a theoretical basis and material support for promoting soybean quality improvement.

Conclusions
Across the Northeast and Huang-Huai-Hai regions, soybean varieties showed an overall increasing trend in oil content through successive breeding generations, while the protein content generally exhibited a decreasing trend.There was a negative correlation between oil content and both protein content and the sum of protein and oil contents, whereas the protein content was positively correlated with the sum of protein and oil contents.Furthermore, these correlations strengthened with decreasing latitude.The stability of quality traits among various resources under various environmental conditions showed significant variation.Hefeng 45, Jilinxiaolidou 4, and Zhonghuang 19 had a relatively high protein content and exhibited good stability across different environments.Kenjiandou 25, Changnong 17, Dongnong 46, Kennong 17, Liaodou 14, and GR8836 all had a relatively high oil content, with stable performance in varying environments.Through multi-point evaluations of soybean germplasm quality traits in the Northeast and Huang-Huai-Hai regions, it was evident that not only was there a large variance in quality among varieties, but the degree of environmental impact also varied greatly.The selection of

Figure 1 .
Figure 1.Distribution of experimental sites within the three regions.Three regions (Group A, Gr B, and Group C) were set with 4, 5, and 6 experimental sites, respectively.The orange circles rep sent the distribution of experimental sites of Group A, with A1-A4 representing Zhalantun, He Jiusan Farm, and Yaergenchu, respectively.The green circles represent the distribution of exp mental sites in Group B, with B1-B5 being Jiamusi, Suihua, Gongzhuling, Tonghua, and Yanb respectively.The purple circles represent the distribution of experimental sites in Group C, w C1-C6 being Shijiazhuang, Handan, Zhoukou, Fuyang, Bengbu, and Bozhou, respectively.

Figure 2 .
Figure 2. Comparison of quality traits of breeds developed in different eras in three regions: (A) protein content; (B) oil content; (C) sum of protein and oil contents.The three columns for each group represent varieties derived in the 1980s, 1990s, and 2000s.The red dots on the box plot represent the mean, while the black lines represent the median.

Figure 2 .
Figure 2. Comparison of quality traits of breeds developed in different eras in three regions: (A) protein content; (B) oil content; (C) sum of protein and oil contents.The three columns for each group represent varieties derived in the 1980s, 1990s, and 2000s.The red dots on the box plot represent the mean, while the black lines represent the median.

Figure 3 .
Figure 3.Comparison of quality traits in different regions: (A) protein content; (B) oil content; (C) sum of protein and oil contents.The red dots on the box plot represent the mean, while the black lines represent the median.

Figure 3 .
Figure 3.Comparison of quality traits in different regions: (A) protein content; (B) oil content; (C) sum of protein and oil contents.The red dots on the box plot represent the mean, while the black lines represent the median.

Figure 4 .
Figure 4. Analysis of quality traits and stability of varieties in Group A: (A) the protein content and coefficient of variation of the germplasm; (B) the oil content and coefficient of variation of the

Figure 4 .
Figure 4. Analysis of quality traits and stability of varieties in Group A: (A) the protein content and coefficient of variation of the germplasm; (B) the oil content and coefficient of variation of the germplasm; (C) the sum of protein and oil contents and the coefficient of variation of the germplasm.Standard deviation (SD).

Figure 5 .Figure 5 .
Figure 5. Analysis of quality traits and stability of varieties in Group B: (A) the protein content and coefficient of variation of the germplasm; (B) the oil content and coefficient of variation of the Figure 5. Analysis of quality traits and stability of varieties in Group B: (A) the protein content and coefficient of variation of the germplasm; (B) the oil content and coefficient of variation of the germplasm; (C) the sum of protein and oil contents and the coefficient of variation of the germplasm.Standard deviation (SD).

Figure 6 .
Figure 6.Analysis of quality traits and stability of varieties in Group C: (A) the protein content and coefficient of variation of the germplasm; (B) the oil content and coefficient of variation of the germplasm; (C) the sum of protein and oil contents and coefficient of the variation of the germplasm.standard deviation (SD).

Figure 6 .
Figure 6.Analysis of quality traits and stability of varieties in Group C: (A) the protein content and coefficient of variation of the germplasm; (B) the oil content and coefficient of variation of the germplasm; (C) the sum of protein and oil contents and coefficient of the variation of the germplasm.standard deviation (SD).

Table 1 .
Varieties used in this study and their breeding years.
NA indicates that the released year is unknown.

Table 2 .
Correlation analysis of quality traits in three regions.
7.22 × 10 −39 The protein and oil contents in Group B

Table 2 .
Correlation analysis of quality traits in three regions.

Table 3 .
Statistical analysis of qualitative traits in different regions.

Table 3 .
Statistical analysis of qualitative traits in different regions.

Table 4 .
List of germplasm with good quality traits and stability in Group A.

Table 4 .
List of germplasm with good quality traits and stability in Group A.

Table 5 .
List of varieties with good quality traits and stability in Group B.

Table 5 .
List of varieties with good quality traits and stability in Group B.

Table 6 .
The list of varieties with good quality traits and stability in Group C.