Variability, Inheritance, And QTL Mapping Of Aluminum Tolerance Traits In Chinese Germplasm Of Soybean

Soybean[Glycine max(L.) Merr.],originated from China,is one of the most important sources of vegetable protein and edible oil world-widely.Recently,the demand of soybean increased year after year in China.The import of soybeans has exceeded the productivity in China and China became the biggest import country in the world.However,aluminum toxicity is one of the main factors limiting soybean growth and productivity in acid soil,particularly in red soil area in southern China. The total area of acid soil is 128 million hm²,widely spreaded in 15 provinces and covered 22.7%land of the country.Therefore,breeding for tolerance to aluminum toxin(Al-tolerance) is a major approach to enhance soybean productivity in acid soil.Up to date,the studies on aluminum toxin tolerance in soybean were mainly involved in morphology,physiology and biochemistry,and only a few on germplasm resources and genetic mechanism of the traits.The main objectives of this present study were(1) investigating the variation of Al-tolerance in soybeans from different eco-regions in China,(2) revealing inheritance of Al-tolerance,and(3) mapping QTLs of Al-tolerance,for providing some basic information to breeding for Al-tolerance in soybeans.Total 509 accessions of Glycine max(L.) Merr.sampled from different eco-regions were tested in a split-plot pot experiment with 28ppm aluminum vs.pure water as major treatment and accession as minor treatment and average membership index over plant height,number of leaves,dry weight above ground and dry weight under ground as tolerance indicator(FAi) in 2006.The results were as follows:(1) There showed a single peak frequency distribution of FAi value with the range of 8.59%～74.83%and the majority in the middle part and less frequencies at both sides, indicating a pretty large variation of Al-tolerance in the whole country,even scattered much more than the tolerant and sensitive checks.The same tendency was for the different eco-regions,with the variation among eco-regions(39.24%～41.65%) being less than that within eco-regions.(2) Total 15(accounted for 2.95%) most Al-tolerant accessions from Eco-regionâ… ,â…¡,â…¢,â…£,andâ…¥with FAi value more than 65%and five(0.98) most sensitive accessions from Eco-regionâ…¡,â…¢,â…£,andâ…¥with FAi value less than 15%were screened out for further studies in genetics and breeding for Al-tolerance.Kefeng NO.1 and Nannong 1138-2,with large difference in Al-tolerance traits were chosen to study the genetic mechanism of Al-sensitive in soybean.Genetic analysis was performed under major gene plus polygene mixed inheritance model in the P₁,P₂,and F_7:11 of the cross Kefeng NO.1×Nannong 1138-2.The results showed that Al-tolerance was controlled by two major genes plus polygenes,with the major gene heritability of 40.55%,and polygene heritability of 47.81%,indicating M-tolerance involved with both major genes and polygenes.Based on the genetic segregation analysis above,QTL mapping for Al-tolerance in soybean was carried out on the genetic linkage map supplied by National Center for soybean Improvement under the methods of composite interval mapping(CIM) and multiple interval mapping(MIM) of software Win QTL Cartgrapher 2.5.With CIM method,five QTLs,i.e.qFAi-1,qFAi-2,qFAi-3,qFAi-4,and qFAi-5,conferring Al-tolerance in soybean were mapped on four linkage groups,i.e.B1,D1b2,D2,and L, explaining 5.20%～9.07%of the total phenotypic variation,respectively,while with MIM method,five QTLs,i.e.qFAi-1,qFAi-5,qFAi-6,qFAi-7,and qFAi-8,explaining 5.70%-24.60%of the total phenotypic variation were detected on four linkage groups, Of which two QTLs,i.e.qFAi-1,and qFAi-5,were located on the same regions of linkage group B1 and L as that under CIM.While qFAi-6 on Dlb2 was close to that under CIM,and with CIM,two QTL located on the two close regions maybe the same QTL,which need to be further identified.Others detected with CIM and with MIM were quite different from those with CIM.The results need to be further verified.