| Cotton,as a raw material for the textile industry,is one of the most widely grown fiber crops in my country.With the support of national policies and changes in population structure,the production methods of cotton producing areas in my country have also undergone great changes.Xinjiang,as the most important cotton producing area in the northwest inland cotton area,has gradually become the largest cotton growing area in my country by virtue of its unique environment and geographical advantages.With the steady improvement of the level of mechanization in cotton production areas,the problem of machine picking cotton is particularly prominent.Mechanical harvesting of cotton reduces labor costs and improves production efficiency,but reduces the quality of cotton to a certain extent.Screening and cultivating suitable for mechanical harvesting the variety of cotton is the foundation for the healthy development of Xinjiang’s cotton industry.In this experiment,by investigating yield,fiber quality,plant type,growth period,defoliation and other traits,a sensitivity analysis system for upland cotton defoliants was constructed,and383 upland cotton germplasm resources were screened for defoliant-sensitive varieties.and identification,and performed genome-wide association analysis(GWAS)between the defoliation phenotype data and the genome resequencing data,and screened and verified candidate genes related to the regulation of defoliation.It provides a theoretical basis for breeding high-quality defoliation-sensitive varieties and mining genes that regulate defoliation.The main findings are as follows:1.383 upland cotton germplasm resources from different regions were treated with defoliants for 2 years.Through the sensitivity analysis system of upland cotton defoliants,a total of 13 sensitive materials and 18 insensitive materials were screened.Through the cluster analysis of multi-phenotypic traits,the defoliant sensitivity of the materials was corrected,and a total of 12 high-quality sensitive materials and 19 insensitive materials were screened,which were basically consistent with the screening results based on defoliation traits..The t-test results showed that there were differences between defoliant-sensitive materials and insensitive materials in terms of the length of the second fruiting branch,the length of the fifth fruiting branch,the length of the eighth fruiting branch,the average fruiting branch length,the plant height,the width of the plant and the flocculation time of the first fruiting branch.significant difference.The analysis results showed that plant type traits and growth period traits could be used as predictive indicators for screening upland cotton defoliant-sensitive varieties.2.In order to compare the effect of defoliant treatment on petiole abscission in field and indoor environments,25 upland cotton varieties with differences in defoliant sensitivity were selected for field and indoor defoliant treatment experiments.The results showed that the defoliation rate of the sensitive and insensitive materials fluctuated the most within 1d-5d after the defoliant treatment in the floc-opening stage.The key period of indoor 10-leaf stage defoliation rate changes was 3d-4.5d(72h-108h),and the leaf abscission of sensitive materials occurred in the lower part of the plant,and the leaf abscission of insensitive materials occurred in the upper part of the plant.The results of indoor abscission observation test and observation of abscission cells in petiole showed that the critical period for the formation of abscission was 2d after defoliant treatment,and the difference in defoliation phenotype between sensitive and insensitive materials was after 72 h.This result provides a time reference for the study of defoliation-related functional genes.3.The relative defoliation rate(RDR)BLUP values of 383 upland cotton varieties and the 1 076 652 SNP markers obtained by resequencing were analyzed by GWAS.A total of the last four significant loci were detected on chromosome A13,and the four loci were located on the signal peaks around5168kb-5214 kb on chromosome A13.Therefore,the interval of 5168kb-5124 kb on chromosome A13 was regarded as a candidate interval for regulating defoliation genes.By analyzing the 37 SNP sites in the candidate interval,the association group was divided into 3 haplotypes and named Hap＿1 ～ Hap＿3accounted for 40.16%,9.56% and 50.27% of the whole population,respectively,and the RDR and RDR＿BLUP values of Hap＿2 and Hap＿1 and Hap＿3 haplotypes were significantly different.4.Sampling at multiple time points on the petioles treated with defoliants at the field opening stage,extracting RNA,and performing quantitative PCR(q RT-PCR)analysis;conducting time gradients on petioles treated with defoliants at the 10-leaf stage indoors Samples were taken,and transcriptome sequencing was performed.Combined with the results of q RT-PCR analysis and transcriptome sequencing,four candidate genes in the candidate interval were identified.Two candidate genes(Gh＿A13G042700.1,Gh＿A13G043000.1)were preliminarily identified.5.In order to explore the role of the above two candidate genes in the defoliation process of upland cotton,materials with significant differences in sensitivity to defoliants were selected as the test materials for the virus-induced gene silencing(VIGS)test.Results Gh＿A13G043000.1 showed no significant difference phenotype,while Gh＿A13G042700.1 showed significant phenotype difference after VIGS.After silencing this gene,the defoliant-sensitive material became insensitive and the defoliation rate decreased.Therefore,preliminary It is judged that this gene is likely to be a functional gene that positively regulates and promotes leaf abscission. |
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