| Soybean[Glycine max(L.) Merr.]originates in China.It is one of the important sources of protein and fat for human.In China,soybean is a major oilseed crop and is grown on about nine million hectares and total output about 16 million ton.Because of high velocity winds and frequent heavy rainfall,lodging is a common problem in production for soybean in the southern China.Lodging damage reduces both harvested yield and seed quality. Therefore,lodging resistance is one of the most important goals in soybean breeding.Lodging represents a quantitative trait and is difficult to assess on a phenotypic basis. Marker-assisted selection(MAS) would become an important tool to improve lodging resistance in soybean.In this study,we mapped and characterised quantitative trait loci (QTLs) for lodging resistance,as well as morphological traits correlated with lodging and yield traits,in a segregating population of 165 recombinant inbred lines derived from the cross of the lodging-resistant soybean variety zhongdou 29 with the susceptible variety zhongdou 32.Field data were obtained in two years.The aim of current study was to explore genetics based on lodging resistance in soybean and gain useful molecular markers for molecular-assisted selection.The results are as following.1.Index of lodging resistance(ILR) made up of different components was designed based on the mechanics as a comprehensive index to determine lodging resistance of 30 spring soybean cultivars.The ILR,(root weight×stem intension)/(plant height×shoot weight×branch number)×100,test at podding stage was significant negative relation with percentage of prostrate plant(r=-0.680).The test result could prove that the ILR might be used as an indicator to evaluate the lodging resistance of soybean objectively and accurately.2.The linkage map including 28 linkage groups with 113 SSR markers.The map covered 1100.1 cM in length with an average marker interval of 9.7 cM,minimal interval of 0.3 cM and maximal interval of 32.4 cM.The order of markers in this map was identical to the order of "Consensus Linkage Map".3.With the method of composite interval mapping(CIM) 45 QTL for lodging and related traits were detected on 8 linkage groups,explaining 4.4%-50.1%phenotypic variation. One QTL(qLD-15-1) of lodging and one QTL(qPH-15-2) of plant height on linkage group F were both detected in two years;one QTL of nodes on main stem and 2 QTLs of root weigh were detected in two years on linkage groups G,A2 and L respectively.The positions of some QTLs of plant height,root weight,shoot weight,stem diameter,nodes on main stem and branch number were close to those of lodging,showed that the lodging resistance is associated with the characters in aerial part and underground portion.The result might provide a basis for the further fine mapping and molecular marker-assisted breeding.4.32 QTLs for yield,seed and pod traits were detected on 6 linkage groups,which majority were located on linkage groups C2,F and I.The QTLs of 100-grain weight and pod number on branch were in same or adjacent marker interval with the QTL of lodging, showed the correlation between yield-related traits and lodging.On linkage group I,the QTLs for yield components of number of seeds per pod,two-seed pod,three-seed pod,and four-seed pod were mapped to the same position in two years,explaining 32%-65% phenotypic variation.The positive alleles of QYLs for number of seeds per pod and four-seed pod,QTLs for two-seed pod and three-seed pod were from different parents,the four QTLs of seed and pod traits were mapped to the same loci.The result was consistent with the correlation analysis of phenotypic traits.The result showed that the regulatory mechanisms of number of seeds per pod and four-seed pod,two-seed pod and three-seed pod were different,which may provide an important basis for promotion of soybean yield by improving seed and pod traits.5.Based on unconditional and conditional QTL mapping methods,13 QTLs for plant height and 13 QTLs for stem diameter were detected on eleven linkage groups.The number, additive effects and contribution rate of QTLs for plant height and stem diameter were different at different measuring stages,which indicated that these QTLs expressed timely and electively.The QTLs of plant height and stem diameter on linkage groups F were mapped to the same loci and they were expressed simultaneously from R1 to R4 stages.In the early stages QTLs expressed more than in late stages,and QTLs for plant height expressed more times than QTLs for stem diameter.The positive alleles of QTLs for plant height and stem diameter were from different parents.The developmental dynamic of QTLs for plant height and stem diameter was consistent with the correlation analysis ofphenotypic traits at different developmental stages.
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