The maturity date of soybean Glycine max L. A total of world soybean varieties, including 48 MG checks, were tested at a major site Nanjing, The maturity date of the world soybean varied greatly 75— d in Nanjing.
The cluster analysis among MGs and subgroups using genome-wide markers validated the MG sequential emergence order and the subgroup differentiation in eight MGs. For future evaluation, in addition to one major site Nanjingone supplementary southern site Soybean maturity groups and one supplementary northern site Heihe are sufficient.
Soybean Glycine max L. Soybean is rich in nutritional value due to its high protein and oil content as well as aspects of its functional composition, such Soybean maturity groups isoflavones.
Along with its dissemination worldwide, soybean has adapted to diverse ecological conditions, especially to the local day length and temperature conditions created by geographic latitude and altitude. Soybean maturity groups most significant trait related to adaptation to diverse environments is growth period, or maturity date.
Originally, soybean was a short-day crop with a sensitive response to photoperiod, as well as temperature. Because day length changes with the seasons, cropping season is another ecological factor determining the maturity date of soybean.
The maturity date varies greatly among soybean varieties around the world, even within a same geographic region. Initially, farmers and early soybean scientists classified soybeans as early, medium and late maturity types.
This classification was extensively used everywhere. However, it was insufficient at comparing varieties from different ecological regions. An early maturing variety in one region may be considered a late variety in another region.
Ultimately, 13 Soybean maturity groups, i. MG00, 0, I, X, were formed in the world. The difference in maturity date between two adjacent groups is approximately 10 to 15 days in an adapted area Norman Categorizing soybeans into different MGs allows for more accurate and quick judgment of the prospects for introducing new varieties and plays an important role in the breeding and production of soybeans in North Soybean maturity groups.
Many soybean scientists in different countries have adopted this MG system and have classified their local varieties into different MGs. Monsanto was the first company to introduce the concept of maturity groups to Brazil Penariol As an increasing number of private companies used the North American system, the traditional Brazilian method of classifying varieties into early, medium and late was gradually replaced with the MG system and was classified into MG VI—VIII.
In China, the traditional way of grouping soybeans was also early, medium and late, relative Soybean maturity groups a local Soybean maturity groups and even to the cropping system Hao et al. In addition, they found that the significant difference in flowering date was related to geographic locations and cropping systems in MG 0, I, II and III and divided each group into two subgroups according to the days to R1 beginning bloom.
It seemed that the early maturity group continued to increase as the soybean area expanded northward and new varieties developed.
According to the trials at nine locations in Northeast China, Fu et al. Fukui and Arai studied the ecological classification of soybean varieties in Japan based on the days from germination to blooming and from blooming to ripening with special reference to their geographical differentiation.
They grouped soybean varieties into five vegetative stage groups Soybean maturity groups three reproductive stage groups in a total of nine combined groups. The growth period structure differentiation among varieties was also studied in China Sun et al. They found that a different structure of growth periods existed within each group of MG 0—III and further divided them into two subgroups: However, no study has been carried out to evaluate the variation of MG of the worldwide soybean varieties under a uniform environment, due to the extreme diversity of the sensitivity to day length and temperature.
The present study aimed to reveal the variation of MGs of the world soybean varieties under a uniform environment Nanjing, China in this study and the distribution of MGs in world geographic regions. The first step was to establish a procedure to Soybean maturity groups diverse MGs for a large Soybean maturity groups of varieties, i.
According to our previous experiences in identifying the Soybean maturity groups of Chinese soybeans Gai et al. The knowledge of the world MG expansion and geographic distribution will benefit both the development of soybean varieties and the exploration of the evolutionary processes of growth period traits.
According to the dissemination paths Soybean maturity groups by Singh and Hymowitzthey were further divided into 13 geographic populations: MG types of world soybean varieties distributed in 13 geographic populations including 48 MG checks.
The field experiments were set in Soybean maturity groups locations: Table 1 shows the entire experimental scheme with the MG checks arranged.
Soybean maturity groups field tests at the major site of Nanjing and its supplementary site of Jining were conducted in two years. Here, spring planting was used for testing the full season response of the materials rather than the local summer planting which is the regular double cropping system after winter wheat.
Inone additional earliest variety Glycine max L. An additional test for late Soybean maturity groups was conducted in Nanjing inin which late varieties were sown approximately 10 days earlier than in and The field test at the supplementary site of Heihe was conducted in two years. In40 early varieties around MG —0 were sown on May 17, and in74 Soybean maturity groups varieties were sown on May Another additional supplementary test was conducted in Mudanjiang inin which early varieties around MG —II were sown on May An additional supplementary test was conducted in Nanning, in which 65 late varieties were sown on July The soybeans were tested in single row plots, 1 m in length and 0.
After emergence, they were thinned to 6—8 seedlings. Soybean maturity groups phenological stages of emergence VEbeginning bloom R1 and full maturity R8 were recorded as Fehr and Caviness described. The flowering date and maturity date were calculated as the period from sowing to R1 and from sowing to R8, respectively.
The maturity dates of Soybean maturity groups 48 MG checks were used as standards for identifying the MGs of each tested material at each site. The MG type of a variety was identified from the results in Nanjing with reference to those in Jining. Therefore, some MGs were separated into subgroups first subgroup and second subgroup.
To save space, the detailed procedure will be explained in the corresponding results section. For revealing the genetic relationship among the MGs, of the varieties were genotyped using RAD-seq restriction-site-associated DNA sequencing. The sequences of the varieties were obtained by using Illumina HisSeq instrument through MSG multiplexed shotgun genotyping method Andolfatto et al. We found that when using the full season conditions in Nanjing, China sown in Soybean maturity groups springall of the Chinese soybean varieties could mature naturally Gai et al.
That means to compare the maturity date of the world soybean varieties Soybean maturity groups a uniform environment in Nanjing, China Therefore, the major site for evaluation of the worldwide soybean maturity date was set in Nanjing.
The evaluation results in the Nanjing I environment indicated a very large variation in maturity date among the world soybeans, ranging from 75— d with an average of Nanjing is better than Jining in its sensitivity for detecting maturity date differences range between 73— d, an average of The frequency distribution of the world soybean maturity date in Nanjing comprised multiple peaks, this indicates that the population of world soybean varieties is a mixture of multiple subpopulations with the extremes as rare types Table 2.
The Soybean maturity groups distribution and descriptive statistics of the Soybean maturity groups date in world soybean varieties including 48 MG checks. The maturity dates in Nanjing I, Jining and Heihe were the average data of and The maturity dates Soybean maturity groups Nanjing II were the data, and the maturity dates in Mudanjiang and Nanning were the Soybean maturity groups.
Table 3 shows the maturity date of the MG checks at five trial sites. This might be because in the higher latitude of Jining According to the data of MG checks in Table 3the reference ranges or boundaries of each MG at each site were determined and listed in Table 4.
The determination of early MGs MG —0 should refer to the grouping in the supplementary sites of Heihe and Mudanjiang. This is because of the delayed Soybean maturity groups date July The reference ranges can be expected to expand to the required size if planted in spring.
Performed the maturity date of the 48 MG checks at each trial site to be used for grouping the world varieties into MGs. The Soybean maturity groups dates of Nanjing I, Jining and Heihe were the average data of and The maturity dates of Mudanjiang and Nanning were the data. According to the grouping criteria in Table 4the world soybean varieties were first grouped according to the Nanjing I and Nanjing II criteria.
Then, the early maturing varieties were further checked successively according to the criteria in Jining, Mudanjiang and Heihe. Among the varieties along with the 48 MG checks in a total of world soybean varieties, the major Soybean maturity groups was MG 0—IV, this part accounted for 8.
This result implied that the major part of the world soybean varieties was in MG 0—IV, or geographically in northern East Asia and northern North America, while modern varieties tended to the early and late MGs along with the soybean expanded northward and southward.
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Table 5 and Fig. The geographic distribution of maturity group MG materials in the world. The different color of Soybean maturity groups represent different MG types of varieties in 13 geographic populations. It is very interesting that in this small area the varieties clearly differed in MGs. This might be due to the multiple cropping systems as well as the warm weather in sea and ocean environments.
A tremendous improvement in soybean occurred in the Soybean maturity groups after it was disseminated to the USA. This might be due to that the USDA widely introduced soybean germplasm from all over the world and left some late MGs grown in this region. Soybean has also been disseminated throughout the whole world and has been genetically improved for adaptation to various latitudes.
More MGs are expected to be possible in areas of high and low latitudes. The boundaries between the two subgroups in a MG were determined from the lowest frequency point in a MG with reference to the corresponding MG mid-value.
The upper limit Soybean maturity groups the first subgroup was equal to the lower limit of the second subgroup in each MG because of the continuity of the trait. The genetic relationship among the MGs of the world cultivated Soybean maturity groups Glycine max L. In the Neighbor-joining dendrogram Fig. It is very interesting that the evolutionary relationship is strictly in a sequential order based on the genome-wide markers.
Un-rooted trees showing the genetic relationship among 12 MGs and 16 subgroups. The first subgroups concentrated in one cluster and the second subgroups scattered in several clusters indicated that Soybean maturity groups all the first subgroups were close to each other and all the second subgroups were distinct from each other but more distinction appeared between the first and the second subgroups.