Maturity Group Classification And Genetic Diversity Analysis Of Maturity Genes In African Soybean Germplasm

Soybean(Glycine max(L.)Merr.)isanon-native and non-staple crop in sub-Saharan Africa(SSA)with potential to be a commercial crop owing to its wide range of uses as food,feed,and industrial raw material.The low soybean yield(about 1.1 t ha-1)in SSA has hindered expansion of the crop into different agro-climatic zones.This low yield necessitates the understanding of natural genetic variations of flowering and maturity genes in SSA soybean germplasm in order to develop effective soybean breeding strategies in SSA.In this study,a total of 125 varieties selected from ISVEX and IITA varieties were genotyped at E1,E2,E3,E4,and J loci,and in parallel were phenotyped for vegetative stage of emergence(VE),and reproductive stages of beginning bloom(R1)and beginning maturity(R7)in Beijing,Yunnan and Hainnan in 2017/18.A wide range of variation was shown among the relative maturity group(RMG)values of the 125 varieties.In Beijing,Yunnan and Hainan,the RMG values ranged from-0.44 to 8.91,5.19 to8.98,and 0.59 to 8.81,respectively.The RMG values of the IITA varieties were ranged from 7.01 to 8.91,6.70 to 8.98 and 3.82 to 8.20,in Beijing,Yunnan and Hainan,respectively.Forty-eight of the 125 varieties had approximately consistent RMG values in the three locations.This consistency in RMG estimates may be due to stability of these varieties in transiting to flowering and maturity across wide range of latitudes.Since almost of these varieties are highly adapted to low latitudes in SSA,the results of the RMG in this study,would warrant further evaluation of these varieties in SSA.Eleven E haplotypes at E1,E2,E3andE4,and four J haplotypes,each two haplotypes for the functional J alleles(HT1 and HT3 haplotypes)and the loss-of-functional jalleles(HT1m and HT3 m haplotypes)were identified across the 125 varieties.The existence of an apparently functional J alleles in the studied IITA late-flowering varieties adapted to low-latitude regions in SSA,suggests that Jlocus which is conferring the long-juvenile(LJ)trait is not the only locus responsible for this trait.Comparing allelic combinations of E1,E2,E3 and E4,and J with the previous grain yield of 36 selected varieties,revealed that e1-as/E2/E3/E4/HT1 and e1-as/e2-ns/E3/E4 haplotypes corresponding with MG IV and V were associated with the high-yielding of the varieties in the maturity zones 8 and 9.This indicates that for South Africa,the leading soybean-producing country in SSA,which is suited in zone 9,soybean varieties which have e1-as/E2/E3-Mi/E4/HT1 and e1-as/e2-ns/E3-Ha/E4 haplotypes and belong to MG IV and V are highly suitable for achieving high-yielding of soybean in this country,and in another countries located in the two zones.It is quite clear that the four haplotypes E1/E2/E3/E4/HT1,E1/E2/E3/E4/HT3,E1/e2-ns/E3/E4/HT1 and E1/E2/E3/E4 corresponding with MG VII and VIII have played a major role in increasing soybean yield and productivity in Nigeria,Zambia,Malawi,Uganda,Sudan,Benin,and Togo,since 7 IITA varieties which have the same haplotypes and maturity groups were released for commercial production in these countries.These findings indicate the important of these four haplotypes and MG VII and VIII in increasing the low soybean yield in SSA countries.The results of this study provide core knowledge about maturity groups and allelic combinations of flowering and maturity genes that have contributed in increasing soybean adaptation and productively in SSA.To develop a maturity group system for specific latitudes in SSA,similar to what have been done in North America and China,the key points to this system would be days to flowering,days to maturity,and plant height at specific latitudes based on the allelic combinations underlying the photoperiod and plant architecture.