| World demand for cotton is growing at a rapid pace,far greater than the world population growth rate.Thus,it always has been an attention of the world-wide cotton breeding programs to improve Upland cotton cultivars in terms of high yield with acceptable fiber quality.Both fiber quality and yield traits are complex traits which are controlled by a magnitude of quantitative trait locus(QTL).There is a complicated genetic correlation among fiber and yield traits because of the different population types and parental lines.Thus,improving both fiber quality and yield simultaneously is a long-term task for cotton breeders.The allotetraploid species,Gossypium hirsutum,is cultivated widely throughout world with high yield and moderate fiber quality,but its genetic basis is narrow.The genetic base could be extended by utilization of wild species because their genetic basis is wide and they possess many excellent traits.In this study,a set of 107 introgression lines(ILs)was developed with interspecific cross using G.hirsutum acc.4105 as recurrent/background parent and G.tomentosum(AD3)as donor parent.The objectives of present study were to evaluate the phenotypic performance of IL population for yield and fiber quality traits across three environments,to identify the QTLs from the wild G.tomentosum species for the fiber quality and yield traits,and to identify QTL clusters of yield and fiber quality traits on the chromosomes.These ILs along witix its recurrent parent were evaluated in three environments for two years.Taking altogether,the developed IL population is very rich genetic material which possessed great diversity in introgressed segments from wild G.tomentosum species.The coverage of introgressed components is much higher in the At sub-genome than Dt sub-genome.The introgressed segjments represented the 34.54%of the genome of tetraploid cotton.The highest coverage was on the A13 and this genomic region in the ILs could be focused in future cotton breeding programs.Phenotypic performance of ILs revealed that introgressed segments from G.tomentosum have greatly affected the both fiber quality and yield in the ILs.More than half of the ILs were found to be with better fiber quality and improved yield traits.Specific locus amplified fragment sequencing(SLAF-seq)was used in this study to obtain high-throughput SNP markers.Overall,265.20 Mb pair-end reads were generated by SLAF-method.After pre-design scheme,pilot experiment for ensuring the marker density,uniformity and efficiency,and filtering low depth SLAF tags,eventually 3157 polymorphic SNP markers were identified for further studies.The integrity and the precision of SLAF markers were higher.The distribution of markers was unevenly,as maximum number of markers(1816)was identified in At sub-genome as compare to Dt sub-genome(1341).In total,74 quantitative trait loci(QTLs)were detected.Of these,30 QTLs were detected for five fiber quality traits and 44 QTLs were detected for eight yield traits.Among the 74 QTLs,47 QTLs(63.51%)were identified in the At sub-genome as compared to Dt sub-genome(27 QTLs,36.48%).Overall,69 markers were found to be associated with 74 QTLs in this study.Forty markers were associated with yield,and 29 markers were associated with fiber.More than half,44 QTLs(59.45%)in this study showed positive additive effects for yield and fiber traits,suggesting that segments from donor parent improved the yield and fiber quality significantly.Nine QTLs were detected in environment 1,29 QTLs were detected in environment 2 and 36 QTLs were detected in environment 3.In present research,a few of genomic regions containing QTL clusters were examined,mainly on the chromosomes A01,A09,A135 D02 and D10.These QTL clusters affected two or more different yield and fiber quality traits.The highest number of QTLs was observed on A01 and A 13-cluster where 5 QTLs were detected on each cluster for fiber strength,lint percentage,boll number,100-seed weight,and plant height and seed index. |
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