| Acid rain has been a major environmental issue worldwide for several decades and it has detrimental effects on human health,aquatic and terrestrial ecosystems,forests and crops.Although policies and measures have been adopted by many countries successively to control acidic deposition,the problem will continue to be present for a long time.Further researches on the tempo-spatial changes of acid rain features and it's precursors are necessary to guarantee effectiveness and success of studies on the subjects related to acid rain.Soybean is the largest source of edible vegetable oil for human and high protein feed for animal.Acid rain has many harmful effects on soybean growth,including inhibiting seed germination,injuring leaf,decreasing photosynthesis,damaging plasma membrane,reducing growth of root nodules,and finally causing seed yield reduction.Different genotype of soybean possesses distinct response to acid rain stress,this gives promise for genetic improvement of acid rain tolerance in such crop;however,the numbers of germplasm used in these investigations were very small and wild soybean,which is a very import part of the gene pool,had not been included,genetic variation and diversity of acid rain tolerance in soybean have not ever been well evaluated.Acid rain tolerance is a complex quantitative trait,which is governed by multiple genes and influenced by features of acid rain(occurrence time,intensity,duration,and frequency,etc.);although effects of acid rain on morphology,physiology and yield in soybean have been widely examined,genetic mechanism of acid rain tolerance has not been explicated.All of these motivates drove us to do the following explorations:(a)The tempo-spatial characteristics of acid rain and local area and long-range transport of it's precursors were exemplified in Jiangsu province to clarify their development trends.(b)Genetic variability and diversity of acid rain tolerance were evaluated in a large collection of cultivated and wild soybean accessions sampled from different ecological regions in China using growth,yield and yield components as indices,and the germplasms with different tolerance grades were further screened.These selected germplasms will serve as materials in the subsequent researches for revealing genetic mechanism of acid rain tolerance and selecting or developing tolerant varieties in soybean;(c)GWAS analyses were performed by associating the traits related to acid rain tolerance with polymorphic SSR markers distributed on the whole soybean genome to identify QTLs controlling the tolerance traits.Then,the superior alleles on those important loci were mined and the corresponding carriers were determined.These results could provide some good information for cloning of the genes underlying the tolerant traits,illuminating molecular genetic mechanisms of acid rain tolerance,and developing tolerant varieties through marker assisted selection in soybean.The main contents and results were as following:(1)Tempo-spatial characteristics of acid rain and local area and long-range transport of it's precursors in Jiangsu province Recent acid rain and urban pollutant emissions data from Jiangsu province were used to analyze the spatial distribution of acid rain.Further,the regional air pollution data of the commission discharge atmospheric research database(EDGAR)regional air pollution data were analyzed and a back-trajectory model was developed for the cluster analysis of the air mass transfer characteristics of acid rain.The results showed that from 2007 to 2013 the precipitation pH were high in northern and low in southern parts of Jiangsu Province.The average precipitation pH in the northwest and northeast parts were higher than 5.6;the frequency of acid rain in the area south of the Huaihe River accounted for more than 50%of total rainfall samples.Precipitation conductive in the northwest and southwest was greater than 60?s/cm.The SO2,NOx,and PM10 were lower in the northern part and higher in the southern part.The northern part had higher pH and lower emission of precursors.One likely source for high ammonium and calcium concentration was local soil.From the northwest air mass,the acid rain appeared to have the highest average pH and the air mass from the southwest had the highest percentage of acid rain.The local emission(SO2,NOx,and Dust)reduction from 2005 led the haze and the acid rain problems mitigated to a good trend.The haze day increased and acid rain decreased due to the NH4+,and Ca2+-increase,and the long-distance transmission and the alkaline pollutant played an important role in Jiangsu' acid rain problem and haze since 2009.(2)Genetic variability evaluation and germplasm screening of acid rain tolerance in soybean in China A germplasm collection of 441 cultivated soybean(Glycine max)and 172 wild soybean(Glycine soja)accessions sampled from different ecological regions in China were pot-planted in both 2009 and 2010.Two simulated rainfall treatments with pH 4.2(the simulated acid rain treatment)and pH 5.6(the check)were applied during periods from three leaves to maturity.After maturity,14 traits related to acid rain tolerance in soybean were determined.The joint analysis of variance(ANOVA)showed the two-way interaction effects of genotype*treatment were highly significant(P<0.0001)for all the 14 traits,and this suggested that genetic variability of acid rain tolerance was really present in the gene pool of soybean;Furthermore,the three-way interaction effects of genotype*treatment*year were also highly significant(P<0.0001)for SYPP(Seed yield per plant),TPNPP(Total pod number per plant),SNPP(Seed number per plant),and DMVOPP(Dry matter of vegetative organs per plant),and this indicated that acid rain tolerance for a given soybean genotype might vary in different year when it was measured by the four traits.Analysis of acid rain tolerance coefficients(ARTCs)for the 14 traits in both the G.max subpopulation and the G soja subpopulation demonstrated:SYPP,TPNPP,FPNPP(Fruited pod number per plant),SNPP,and DMVOPP were most sensitive to acid rain stress,and genetic variation for sensitivity of these five traits were large;HSW(Hundred seed weight)was not affected averagely under acid rain stress,but it was influenced on the level of genotype and genetic variation for sensitivity of this trait was present;SNPFP(Seed number per fruited pod)was not sensitive to acid rain stress,and genetic variation for sensitivity of this trait was small.According to response strengths to acid rain treatment for the 14 traits,magnitudes of genetic variations for the ARTCs among genotypes,and correlations among these traits,seven traits,including SYPP,SNPP,HSW,TPNPP,DMVOPP,PH(Plant height),and EBNPP(Effective branch number per plant)were chose for comprehensively evaluating acid rain tolerance of the sampled soybean germplasms using the average subordinate function.Finally,22(8)high acid rain tolerance germplasms and 23(9)high acid rain susceptibility germplasms were screened out from the tested G.max(G soja)subpopulation.Seed yield changes in these accessions with divergent tolerance were mainly attributable to changes in TPNPP,which further led to corresponding alterations in FPNPP and SNPP,and secondarily were due to variations in HSW.(3)Association mapping of QTL for traits related to acid rain tolerance in soybean GWAS analyses were performed by associating the traits related to acid rain tolerance with 79 polymorphic SSR markers distributed on the whole soybean genome in the G max subpopulation,which comprised of 427 cultivated soybean accessions,and the G soja subpopulation,which included 162 wild soybean accessions,respectively.Analysis of genetic diversity showed the averaged numbers of alleles on each SSR locus were 5.9620 and 6.1266 and overall gene diversity were 0.6573 and 0.7255 in the two association panels,respectively;these indices proved that there were extensive genetic variation in the two panels.Inference of population structure revealed that there were both distinct differentiation and some kind of ancestry admixture between the two subpopulations,and hierarchical levels of structures were present in each subpopulation.Computation of kinship relationship matrices(K)indicated that 23.18 and 20.89%of pairwise kinship coefficients were larger than 0.05 in the two subpopulations,respectively,which demonstrated that these were some correlation among germplasms in the two mapping panels.Therefore,the mixed linear model[MLM(PCA+K)]in TASSEL 2.1 was used for GWAS to control the possible spurious associations.In the G.max subpopulation:When the traits related to acid rain tolerance were directly used as independent variables in the MLM model,22 significant(P<0.01)MTAs(Marker-trait associations),with R2(phenotypic variance explained by the single QTL)ranged from 1.14 to 19.06%,were detected;Among these QTL,7 MTAs were discovered under the two simulated rainfall treatments,6 MTAs were found only under the simulated acid rain treatment of pH 4.2(pH 4.2 SAR),while the remainder 9 MTAs were identified only under the simulated rain treatment of pH 5.6(pH 5.6 SR).When ARTCs for those traits were used as independent variables,19 significant MTAs,with R2 varied from 3.25 to 9.17%,were detected.Seven SSR loci were associated with multiple traits;Most interestingly,Satt575 on Gm15 was related to nine traits,including SYPP,SNPP,HSW,and so on,and the predominant superior allele for this locus,Satt575262,was carried by 9 accessions of the 22 high acid rain tolerance G max germplasms.In the G.soja subpopulation:When the traits related to acid rain tolerance were directly used as independent variables,16 significant MTAs,with R2 ranged from 1.06 to 43.32%,were identified;Among these QTL,only 1 MTA was detected under the conditions of both pH 4.2 SAR and pH 5.6 SR,7 MTAs were found only under the condition of pH 4.2 SAR,while the other 8 MTAs were uncovered only under the condition of pH 5.6 SR.When the ARTCs were used as independent variables,17 significant MTAs,with R2 varied from 1.08 to 44.52%,were detected.Seven SSR loci were associated with multiple traits;Most impressively,Satt567 on Gm07 was related to ten traits,including SYPP,SNPP,TPNPP,etc,and the predominant superior allele for this locus,Satt567118,was held by 6 accessions of 8 high acid rain tolerance G soja germplasms. |
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