| Cotton is an essential fiber crop with featured characteristics of providing lubricant for industry,organic matter to soil,meal & hull as livestock feed along-with provision of many basic human necessities.Cotton holds salt tolerant property to some extent.However,excessive amount(of optional salts)adversely affect plant growth & development and eventually lead to death.These adverse effects can be quantified by measuring morphological,physiological as well as biochemical parameters at different growth stages.Loss of resistance/tolerance is mainly due to the narrow genetic base of cotton which badly necessitates the search of valuable genes from the wild cotton gene pool.This can be achieved nowadays with the aid of DNA Markers technology.The identification of QTLs related to salt tolerance can definitely facilitate cotton development in demand.The main objectives of this study were i)to screen salt tolerant germplasm lines,ii)to identify salt tolerant QTLs,iii)to map the putative genes related to salt tolerance.To achieve these objectives,a RIL population(F6:8)derived from a cross between upland cotton lines,LYM-28 as parent 1(P1)and XLZ-24 as parent 2(P2),was used.In the first experiment,these accessions were evaluated in sand culture under a series of NaCl treatments,75,100,125,150 and 175 mM,for germination respectively.Based on the results at the germination stage,125 mM was recommended to be the most suitable NaCl treatment for checking the difference of salt tolerance among the accessions as a basal dose.For further confirmation,to learn the response of high NaCl dose(150 mM),the accessions were grown in sand and hydroponic culture for two weeks after final treatment.The results showed significant differences in the accessions and finally,21 salt tolerant accessions were selected.A linkage map which totally covered 2477.99 cM of the upland cotton genome with 4851 markers,and the software of Windows QTL Cartographer 2.5 using composite interval mapping(CIM)method were applied to analyze the total 16 phenotypic parameters to identify QTLs related to salinity tolerance.A total of 262 QTLs were identified in saline condition,61 of which were common with previous reports while 201 novel ones.Fifty-five QTL clusters were identified to be formed by one hundred and ninety-eight out of 262 QTLs on twenty-four chromosomes.And 10 QTLs,which were detected at least in two environments with 2.28-7.54% of phenotypic variances explained,were termed as stable ones.From these stable QTLs one was already reported,and 9 new.Out of these 10 QTLs,six were related to germination,four to leaf and shoot fresh weight.Most of the QTLs showed the negative additive effect which means most of salt tolerant genes came from more tolerant parent XLZ24.Totally 916 genes were presented within the confidence interval of 10 stable QTLs,out of which 21 genes expression was very prominent under control and stress conditions in the root,shoot,and leaves.It was noted that 3 genes were upregulated,1 was down-regulated and 17 genes were differentially expressed.Candidate gene identification and gene ontology analysis revealed that the genes involved in ion binding,ion transport,ion transferase,defense response,and ion homeostasis may have an important role in improving salinity tolerance.Moreover 28 genes belong to those gene families were found to be involved in salinity tolerance in different crops including eggplant,Arabidopsis thaliana and rice.From these results,it was concluded that the QTLs identified in the present study will provide new genetic resources for improving the tolerance of cotton varieties against salinity stress using molecular breeding strategies in the future. |
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