| Drought is the most important factor restricting maize yield.It is an effective way to increase maize yield by exploring the mechanism of drought tolerance of maize,identifying drought-tolerant genetic resources and combining traditional and molecular breeding techniques to develop new varieties of drought-tolerant maize.In this study,173 inbred lines of maize DH population were identified by pot experiment in green house.The traits of shoot and root systems were used to evaluate and analyze the changes of maize under drought stress.A high-density genetic map was constructed using whole genome SNP markers.The Inclusive Comeposite Interval Mapping method was used for QTL mapping of drought tolerance traits.The main results are as follows:1.In the spring and autumn of 2017,drought tolerance evaluation of seedlings of the 173 DH inbred lines were carried out,respectively.The phenotype data of 16 traits including average root diameter(RD),root forks(RF),root total length(RTL),root volume(RV),root surface area(RS),root tip number(RTN),maxium root length(MRL),ratio of root to shoot(RRS),root relative water content(RRWC),root fresh weight(RFW),root dry weight(RDW),grown amount(GA),total leaf number(TL),shoot relative water content(SRWC),shoot fresh weight(SFW)and shoot dry weight(SDW)under well water and water stress condition were collected,respectively.According to the statistical analysis,the results showed that all the traits were significantly changed under WS compared to that under WW conditioin.The broad-sense heritability of various traits was moderate to hight(0.5-0.8).Most of the paire-wise correlations aomong the traits were significant or extremely significant.In the principal component analysis,each trait played an important role in the first 5 or 3 principal components in the spring and autumn experiments,respectively.Therefore,these results indicated that the tested traits can be indicators that reflecting the growth of plants under drought stress well.2.The comprehensive drought tolerance index(D value)was introduced to evaluate the drought tolerance of the DH population.According to the D value,the inbred lines were divided into three different types:drought-sensitive,medium drought-tolerant and drought-tolerant.In the spring experiment,12 drought-sensitive and 11 drought-tolerant inbred lines were identified,respectively;in the autumn experiment,10 drought-sensitive and 9 drought-tolerant inbred lines were identified,respectively;in addition,two different inbred lines were grouped into drought-sensitive type and drought-tolerant type in both the two trials,respectively.3.A total of 20503 informative SNPs were obtained of the maize DH population by using GBS technique.Using those SNPs,a genetic linkage map was constructed with 437 block markers and 981.77 cM in length.The average genetic distance was 2.24 cM,and each block contained 46.92 SNPs on average.In the quantitative trait loci(QTL)mapping for drought tolerance traits,23 QTL were identified in the spring experiment.Among them,there were 8 major QTL(PVE>10%).In the autumn experiment,10 QTL were mapped,out of which 7 were major QTL.Moreover,in the combination analysis of the two trials,26 QTL loci were mapped,out of which 11 QTL have major effects.4.In combination with the transcriptome analysis of maize roots under drought stress,162 key candidate genes related to energy metabolism,hormone regulation,redox and other biological processes were identified based on the changes in gene expression and gene function annotation.Out of the 162 genes,61 and 101 were significantly up-and down-regulated,respctively,which could be focused on as key research objects for uncovering the mechanism of maize drought tolerance. |
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