| Crop germplasm with abundant genetic variant is basic material for crop breeding program. The long-term breeding practice fully prove that crop released cultivars were important germplasm. Total1300soybean cultivars had been released in China from1923to2005. The knowledge of genetic base and their change for recent years of soybean cultivars can be useful for setting the approaches and steps of genetic base-broadening in soybeans in China.The genetic base of crop was elucidated efficient by the pedigree analysis, especially the population genetic base of crop; The soybean breeding pedigree data with abundant information of pedigree and parents selection for approximate hundred years was ideal for the their population genetic base. Based on an analysis of pedigree data of the1300soybean cultivars released, simple sequence repeats (SSR) molecular marker161pairs of primers located on well-distributed20molecular linkage groups (MLG) and coefficient of parents (CP). The objective of this study is to make a thorough analysis on the population genetic bases of soybean released cultivars; summarize the relation between geographical source and genetic contribution of ancestor from soybean cultivars released in various decade; determine genetic similarity and relationship among cultivars; so as to provide relevant information for further breeding plans of soybeans parents selection and enlarge sources parents up to broadening the genetic base released cultivar. The main results were as follows:1. Total1300soybean cultivars were released in China from1923to2005,682,395,64,120,16and23were released in Northern China single cropping spring planting varietal eco-region (I), Huang-Huai-Hai double cropping spring and summer planting varietal eco-region (II), Middle and Lower Changjiang valleys double cropping spring and summer planting varietal eco-region (III), Central-south multiple cropping spring summer and fall planting varietal eco-region(IV), Southwest plateau spring and summer planting varietal eco-region (V) and South China tropics multiple cropping all season planting eco-region (VI),1019、202、70and9were developed from artificial hybridization, natural variant selection, mutation and transfer DNA, respectively. These cultivars was traced back to670nuclear and344cytoplasmic ancestors; Some major ancestors were cultivated early major cultivars (such as Mancangjin, Zihua si hao, Xudou1hao, Qihuang1hao and Nannong493-1), which were bred more new cultivars, after many breeding cycles, major ancestors were developed the complicated ancestor family. Nowadays some major ancestor from I, II and III, IV, V, VI eco-region go through5-8,5-7and3-5breeding cycles, respectively.1391soybean accessions were selected with direct crossing parent, which included the majority of cultivars and breeding lines and a little landraces and foreign countries cultivar. In order to process of breeding, some important cultivars (such as Hefeng25、Jilin20, Xudou1hao, Qihuang1hao, Aijiaozao, Nannong493-land Shishengchangye etc.) were used for direct crossing parents time after time. Parental combination of71.78%soybean cultivars released were the four parent combination between cultivars (C) with breeding line(S)(CxC、SxS、C×S、SxC) in China, and were more83.5%recent ten years.2. Total670ancestors were composed of landraces, breeding lines, improved cultivars, wild accessions and uncertain type, come from Eco-region I, Ⅱ, Ⅲ,IV, V, V I and foreign countries. Both nuclear and cytoplasmic germplasm from Eco-region I, II, III and foreign countries accounted for most part of the ancestry of the released cultivars. The exchange and utilization of germplasm among eco-regions were poor and mostly still limited in their own eco-regions. The most part of the ancestors was used in only1-2released cultivars, while only a few ancestors provided large genetic contribution but still limited basically in their local ancestors. Such as from eco-regions I Jinyuan(A146), Silihuang (A196), Baimei (A019), Ⅱ Binhaidabaihua(A034), Shandongzhangshou landrace (A295), Huaxiandaludou (A122), Tongshantianedan(A231), Jimoyoudou(A133), III (Fengxiansuidaohuang(A084),51-83(A002), Shanghailiuyuebai(A201). The113core ancestors out of the670were nominated according to the number of derived cultivars, nuclear genetic contribution, cytoplasmic genetic contribution and number of breeding cycles of each ancestor. Among them,34,28,10,14,4,3and20were from I, Ⅱ, Ⅲ, IV, V, VI eco-region and abroad, respectively. It accounted for16.87%of the total ancestors and provided70.90%nuclear and74.85%cytoplasmic genetic contribution to the whole released1300cultivars.3. The average number of ancestors per cultivar released between1996to2005in various eco-regions was about double or more of that between1986to1995. The genetic base of a single cultivar is relatively narrow for most of the released cultivars but has been gradually broadened, especially in Eco-region Ⅰ and Ⅱ; and the average number of ancestors per cultivar released between1996and2005in various eco-regions was approximately double of the period between1986and1995. The of pedigree of recent cultivars were more complication than early ones because scale of cross-breeding and parent combination between cultivars with breeding line raise recent years.4. The analysis of parentage coefficient showed that the genetic base of recent cultivars (1923-1985) were more broad than early ones. The genetic base of cultivars for Ⅱ eco-region was most broad, and Ⅲ eco-region was most narrow among Eco-region Ⅰ, Ⅱ, Ⅲ and Ⅳ. Among ten ancestors family, the genetic bases of Ⅱ eco-region such as A295, A122, A231and133family released cultivars is broad, Ⅲ eco-region such as A084, A002, A201and Aijiaozao (A291)family were narrow.5. Based on analysis of SSR marker of polymorphism information content (PIC) and alleles, we find that The specifically existent alleles, complementary alleles and PIC of recent cultivars (1986～2005) was more than early cultivars (1923～1975), and the specifically deficient alleles was low. The results showed that the genetic base of recent cultivars (1923-1985) were more broad than early ones. The genetic base of cultivars were was related to geographical district of cultivars. The geographical district Ⅰ and Ⅱ eco-region is far and the number of complementary alleles were most, so the genetic relationship between them and was far. On the contrary,The geographical district Ⅰ and Ⅱ eco-region is near and exchange of germplasm was much, the number of complementary alleles were low, so the genetic relationship between them and was close.The result of analysis of genetic structure of the population, specifically existent alleles and genetic similarity were indicated that the genetic base of cultivars were was related to geographical district of cultivars. For example, A201and A291ancestor families cultivars from south region was the geographic distribution in Hunan, Hubei, Sichuan and Jiangxi province and was almost clustered in same group.The number of alleles of A201and A291ancestor family from south regions was more low than ones of A034, A231and A133ancestor family from Ⅱ region. Genetic diversity level in recent cultivars (1986～2005) was higher than that in early cultivars (1923～1975). The different geographical district cultivars can be differentiated by two methods and reveal the distribution of ancestor family characteristic. For example, A201and A291ancestor families cultivars from south region was the geographic distribution in Hunan, Hubei, Sichuan and Jiangxi province and was almost clustered in same group.6. The average genetic similarity indicated the genetic variant and relationships of among cultivars in DNA level. The degree of relationship between the similarity matrices based on SSR and pedigree was measured by comparing the similarity matrices with the normalized Mantel test. A low positive correlation between the two matrices was observed. based on pedigree analysis and genetic similarity SSR markers was different. Parental genetic contribution can be estimated by from pedigree or from molecular marker data; there are three ways to calculate CP by pedigree, GC and SC by marker. We studied37soybean inbreeds with known pedigrees. The inbreeds were genotyped using161SSR markers. Parental contributions were estimated from marker similarity among an inbred and both of its parents, and were subsequently used to estimate CP. Estimates of parental contribution differed significantly between pedigree data and marker. The parental genetic contribution estimated from GC and SC was highly correlated. We concluded that female parental contribution estimated from marker data was more than male one when both parents were same one from pedigree data.The study of distribution of recombination events show that the number of alleles from female parent were more than male parent. There was the difference of number of transition alleles among linkage groups, the linkage group C2, A2, J and F have much more number of transition alleles, but I was least. Recombination events of latest cultivars was more than old one. |
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