| As an important natural fiber crop,the hybrid cotton shows significant heterosis.However,the mechanism of heterosis is still vague on cotton.In the present study,we generated the maternal and paternal backcross(BC/M and BC/P)populations based on the recombination inbred line(RIL)population,which derived from a hybrid of "Xinza 1" on Upland cotton.We performed a BC/M experiment in four environments and a BC/P experiment in three environments,respectively.We collected phenotypic datasets for yield and yield components,fiber quality traits and dynamic boll number in BC/M,RIL-M,BC/P and RIL-P populations,including two mid-parent heterosis value(MPH-M and MPH-P)datasets for yield and yield components and dynamic boll number per plant.A SSR genetic map and a new Bin-map were used to map and analyze QTLs in order to dissect the mechanism of heterosis on Upland cotton.The main results see as follows:A maternal backcross population(177 individuals)and a paternal backcross population(177 individuals)were generated by backcrossing 177 RI lines with GX1135 and GX100-2,respectively.Combining with the control set,a total of seven field trials were performed following a randomized complete block design.Every backcross hybrid interplanted in the middle of parents.Phenotypic datasets were collected for yield and its components,fiber quality and dynamic boll number.Based on genotyping-by-sequencing(GBS)method,we constructed a Bin-map using the sequencing data,which contained 2859 bins with an average marker interval of 0.785 cM.We preliminarily analyzed QTLs and heterosis mechanism in two backcross populations using the SSR genetic map.At single locus level,71 QTLs including 35 common QTLs were detected for yield and its components in multiple populations of two backcrossing experiments.Twenty-eight common QTLs validated the previous results.We analyzed two physical regions for candidate functional genes.A total of 12 and 15 heterotic loci were identified in BC/M and BC/P populations,respectively.No common heterotic locus shared but some heterotic loci overlapped with QTLs,indicating that the QTLs cause heterosis at the same time.In both backcrossing populations,partial dominant and over-dominant QTLs contributed to heterosis at single locus level.QTLs × environment interaction affects heterosis in the present study.In multiple populations of two backcrossing experiments,a total of 37 QTLs were detected for fiber quality traits in the present study,including 12 common QTLs detected in multiple populations or environments.A total of 16 QTLs explained over 10%of phenotype variation(PV).Among these QTLs,19 QTLs explained 5.01-22.09%of PV in BC/P population.Particularly,qFS-Chr3-1,qFE-Chr2-2 and qFM-Chr9-1 explained more than 22%of PV,respectively.A total of 32 dynamic QTLs for boll number were detected in five environments in the present study,including 10 common QTLs.We could identify QTLs at all of t1,t2,t3 and t4 stages in BC/M and BC/P populations.Six QTLs were repeatedly identified at more than one stages.A heterotic loci of qBNP-Chr3-2 was detected at t2 and t4 in BC/M population in the environment of 2016E2.Another heterotic loci qBNP-Chr25-1 was identified at t3 and t4 stages in BC/P population in 2016E2.Using the Bin-map,a total of 118 QTLs for yield and yield-component traits and 53 QTLs for fiber quality traits were detected by CIM method,including 59 and 20 common QTLs,respectively.A total of 25 and 19 heterotic loci were detected in BC/M and BC/P populations.And large number of M-QTLs,E-QTLs and QTL X environment interactions were identified.The results based on the new Bin-map validated the results above using the SSR genetic map.A total of 25 and 19 heterotic loci were identified in BC/M and BC/P populations,respectively.Some heterotic loci overlapped with QTLs,indicating that the QTLs cause heterosis at the same time.In both backcrossing populations,partial dominant and over-dominant QTLs contributed to heterosis at single locus level. |
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