Construction Of Genetic Linkage Map Based On RIL Population Of Upland Cotton (G. Hirsutum L.) And QTL Mapping For Yield And Fiber Quality

Cotton is an important cash crop in the world,which not only contributes the natural fiber for texture industry,but also is an important resource for edible oil and potential protein.So cotton production plays a very important strategic status in our national economy.Cotton yield and fiber qualities have been improved more through the hard working of cotton breeders over the past years with convetional breeding methords.However,with the development of technology in textile industry and improvement of people life level,a higher demand for fiber production and fiber quality is put forward.The complicated genetic mechanism for the cotton yield and fiber quality,as well as the negative relationship between them lead it too difficult to improve at the same time based on the conventional breeding methods.The development of molecular biology and molecular genetics makes it possible to dissect the composite genetic factors controlled the quantitative traits in cotton into the single genetic factor,so it is possible to manipulate quantitative traits by tracing the related molecular markers and QTLs,which may realize improving cotton yield and fiber quality through molecular marker assisted selection(MAS) in cotton breeding.The present research focused on construction of a molecular genetic linkage map based on intra-specific RIL population of upland cotton with SSR,RAPD and SRAP. Based on this map,the QTLs related with cotton yield and fiber quality under multi-environment investigation were mapped.In addition,an IF₂ population was established based on the RIL population and its characteristics and utilization in fiber quality QTL mapping were explored as well.The main results of present work were as follow:(1) An intra-specific RIL population was construed through the way of modified single-hill(bulked progeny row),using two upland cotton parents., MARCABUCAG8US-1-88 and HS46(female),the former is a cotton germplasm with good resistance and the latter is a commercial cultivar with higher yield and good fiber quality.The two parents were different greatly in genetic relationship based on pedigree analysis.The cotton yield and fiber quality,as well as their related traits,had a wider variation ranges among the RIL population,and almost all the traits investigated were normal distribution,which showed that the cotton intra-espcific RIL population is an excellent population for genetic research and QTL mapping.(2) A relatively higher density genetic linkage map was constructed based on the RIL population,using three kinds of molecular markers,SSRs,SRAPs and RAPDs.The map contained 388 markers,covered 30 linkage groups.The linkage map was 1946.22 cM with an average distance of 5.03 cM between the adjacent loci,and spanned 42.1%of cotton genome.So this map is a higher density one for more markers and wide coverage in cotton intra-specific RIL population up to now.According to the anchored SSR markers,15 linkage groups among 30 were assigned to 14 specific chromosomes,and seven A sub-genome chromosomes of them contained 133 markers and covered 683.44 cM,and seven D sub-genome ones included 70 markers and spanned 363.00 cM.These results showed that A sub-genome was larger or had more chance to exchange and combine than D sub -genome in cotton.Compared with previous study,11 chromosomes in this linkage map were found to have some homologous in cotton genome.(3) There were great effects of environment on cotton yield and fiber quality through the combined ANOVA analysis of four environments.So QTL mapping of cotton yields and their related traits were done by the composite interval mapping methods based on linear mixed model.33 QTLs were found for seed cotton yields using the results of cotton yields under four environments,23 QTLs for lint yield,6 QTLs for lint percent,14 QTLs for boll weight,20 QTLs for seed index,and 13 QTLs for lint index.Among the 33 QTLs related with seed cotton yield,21 epistasis QTLs were found,and the total epistasis QTLs contributed more than the additive QTLs.9 QTLs were found to have a significant interactive effect with environments,and 21 epistasis QTLs had a significant effect on the yield,and the interaction effect had greater contribution to cotton yield.These results indicated that the environment had an important influence on cotton yield,and it is hard to develop a wide adaptability upland cotton germplasm with collection of excellent QTLs that adapt to different environments.However,single QTL found to relat with cotton yield has very small effect,and the difference of environments and numbers of environments in experiment maybe affect the genetic effects of QTLs related with cotton yield. Therefore,the genetic obtain for cotton yield may be achieved if more excellent QTLs were collected.(4) 25 QTLs were found to relate with cotton fiber quality in present experiment.Among them,10 pairs of QTLs of them were found to have a significant or very significant epistasis effect,which related to 19 loci located in 13 chromosomes or genetic linkage groups.And these total epistasis effects were found to be higher than that of additive ones.So the epistasis effects played a very important role on the genetic of cotton fiber quality and its related traits. Compared with the yield and its related traits,the number of additive QTLs or epistasis QTLs related with fiber quality were much less than that related with yield and its related trait,which may suggest that the genetic mechanism controlled cotton fiber quality was simpler than that of cotton yield,and the improvement for fiber quality may be easier than that of cotton yield as well. However,the genetic effect of single QTL was very small,it is very difficult to improve cotton fiber quality through the selection of a single QTL.(5) The IF₂ population in cotton was constructed based on the RIL population in present research.The average values of five fiber quality traits investigated were the medial one between the two parents,which did differ insignificantly from the parents and similar or a litter higher than that of F₁ between two parents.The distribution of fiber quality traits in the IF₂ population was all normal distribution.Compared with origin RIL population,the fiber quality traits in the IF₂ population were different insignificantly,and their SD were also very similar except for a few which was higher than that in RIL population.30 QTLs with significant effect or significant interactive effect with environment were mapped in 16 linkage groups based on the IF₂ population and fiber quality traits surveyed in the two environments.17 QTLs of them were related with the effects of dominance,which were located into 15 chromosomes or genetic linkage groups,and the contribution to fiber quality trait variation were more than the other kind of QTLs.Except the single dominant effect locus,the additive-dominant,dominant-additive,and dominant-dominant epistasis effects were found as well,and some of interactive effect of epistasis with environment were significantly.The results indicated that the dominant effect played an important role in the genetic of fiber quality.