Genetics of biochemical attributes regulating morpho-physiology of upland cotton under high temperature conditions

Background Cotton is a strategically important fibre crop for global textile industry.It profoundly impacts several countries’industrial and agricultural sectors.Sustainable cotton production is continuously threatened by the unpre-dictable changes in climate,specifically high temperatures.Breeding heat-tolerant,high-yielding cotton cultivars with wide adaptability to be grown in the regions with rising temperatures is one of the primary objectives of modern cotton breeding programmes.Therefore,the main objective of the current study is to figure out the effective breed-ing approach to imparting heat tolerance as well as the judicious utilization of commercially significant and stress-tolerant attributes in cotton breeding.Initially,the two most notable heat-susceptible(FH-115 and NIAB Kiran)and tolerant(IUB-13 and GH-Mubarak)cotton cultivars were spotted to develop filial and backcross populations to accom-plish the preceding study objectives.The heat tolerant cultivars were screened on the basis of various morphological(seed cotton yield per plant,ginning turnout percentage),physiological(pollen viability,cell membrane thermostabil-ity)and biochemical(peroxidase activity,proline content,hydrogen peroxide content)parameters.Results The results clearly exhibited that heat stress consequently had a detrimental impact on every studied plant trait,as revealed by the ability of crossing and their backcross populations to tolerate high temperatures.However,when considering overall yield,biochemical,and physiological traits,the IUB-13×FH-115 cross went over particularly well at both normal and high temperature conditions.Moreover,overall seed cotton yield per plant exhibited a posi-tive correlation with both pollen viability and antioxidant levels(POD activity and proline content).Conclusions Selection from segregation population and criteria involving pollen viability and antioxidant levels concluded to be an effective strategy for the screening of heat-tolerant cotton germplasms.Therefore,understanding acquired from this study can assist breeders identifying traits that should be prioritized in order to develop climate resilient cotton cultivars.

Comparative analysis of SIMILAR to RCD ONE(SRO)family from tetraploid cotton species and their diploid progenitors depict their significance in cotton growth and development

Background SRO(Similar to RCD1)genes family is largely recognized for their importance in the growth,develop-ment,and in responding to environmental stresses.However,genome-wide identification and functional characteri-zation of SRO genes from cotton species have not been reported so far.Results A total of 36 SRO genes were identified from four cotton species.Phylogenetic analysis divided these genes into three groups with distinct structure.Syntenic and chromosomal distribution analysis indicated uneven distribu-tion of GaSRO,GrSRO,GhSRO,and GbSRO genes on A2,D5 genomes,Gh-At,Gh-Dt,Gb-At,and Gb-Dt subgenomes,respectively.Gene duplication analysis revealed the presence of six duplicated gene pairs among GhSRO genes.In promoter analysis,several elements responsive to the growth,development and hormones were found in GhSRO genes,implying gene induction during cotton growth and development.Several miRNAs responsive to plant growth and abiotic stress were predicted to target 12 GhSRO genes.Organ-specific expression profiling demonstrated the roles of GhSRO genes in one or more tissues.In addition,specific expression pattern of some GhSRO genes dur-ing ovule development depicted their involvement in these developmental processes.Conclusion The data presented in this report laid a foundation for understanding the classification and functions of SRO genes in cotton.

Identification of an Aux/IAA regulator for flesh firmness using combined GWAS and bulked segregant RNA-Seq analysis in watermelon

Watermelon is a highly cultivated fruit crop renowned for its quality properties of fruit flesh.Among various quality factors,fruit flesh firmness is a crucial quality parameter influencing the fruit texture,shelf life and its commercial value.The auxin/indole-3-acetic acid(Aux/IAA)plays a significant role in fruit development and ripening of non-climacteric fruits.However,the regulatory mechanism of Aux/IAA in controlling fruit flesh firmness and ripening in watermelon remains unknown.In this study,we employed an integrative approach combining genome-wide association study(GWAS)and bulked segregant RNA-Seq analysis(BSR-Seq)to identify an overlapping candidate region between 12776310 and 12968331 bp on chromosome 6,underlying an auxin-responsive gene(Aux/IAA)associated with flesh firmness in watermelon.Transcriptome analysis,followed by real-time quantitative reverse transcription PCR(qRT-PCR),confirmed that the expression of Aux/IAA was consistently higher in fruits with high flesh firmness.The sequence alignment revealed a single base mutation in the coding region of Aux/IAA.Furthermore,the concomitant Kompetitive/Competitive allele-specific PCR(KASP)genotyping data sets for F2 population and germplasm accessions identified Aux/IAA as a strong candidate gene associated with flesh firmness.Aux/IAA was enriched in the plant hormone signal transduction pathway,involving cell enlargement and leading to low flesh firmness.We determined the higher accumulation of abscisic acid(ABA)in fruits with low flesh firmness than hard flesh.Moreover,overexpression of Aux/IAA induced higher flesh firmness with an increased number of fruit flesh cells while reducing ABA content and flesh cell sizes.Additionally,the allelic variation in Aux/IAA for soft flesh firmness was found to exist in Citrullus mucosospermus and gradually fixed into Citrullus lanatus during domestication,indicating that soft flesh firmness was a domesticated trait.These findings significantly enhanced our understanding of watermelon fruit flesh firmness and consequently the watermelon fruit quality.

Genome-wide identification and analysis of the CNGC gene family in upland cotton under multiple stress conditions

Background The cyclic nucleotide-gated channel(CNGC)gene family plays a significant role in the uptake of both essential and toxic cations,and has a role in enhancing tolerance to various forms of abiotic stresses as well as the modulation of the heavy metal toxicity to plant through the absorption of heavy metals.Results A complete genome-wide identification and functional characterization of the cotton CNGC genes was carried out,in which 55,28,and 29 CNGC genes were identified in Gossypium hirsutum,G.raimondii,and G.arboreum,respectively.The protein encoded by the CNGC genes exhibited GRAVY value below zero,indicating their hydrophilic property.CNGC genes were unevenly distributed in 19 out of 26 chromosomes,in which the highest density were observed on Ah05,with 8 genes.High gene coverage was observed among the diploid cotton species,with CNGC genes mapped on all A chromosomes and on 11 out of 13 of D chromosomes.The majority of CNGC proteins were localized in the endoplasmic reticulum,nucleus,and plasma membrane.Gene expression analysis revealed the up-regulation of Gh_A01G0520(CNGC4)and Gh_D13G1974(CNGC5)across various forms of abiotic stresses.Moreover,down-regulation of Gh_A01G0520(CNGC4)and Gh_D13G1974(CNGC5)in CNGCs silenced plants caused the significantly reduced ability to tolerate drought and salt stresses.All CNGCs silenced plants were recorded to have significantly low content of antioxidants but relatively higher content of oxidant,including MDA and H_(2)O_(2).Furthermore,SPAD,CMS(cell membrane stability),ELWL(excised leaf water loss),SDW(shoot dry matter weight),and RDW(root dry matter weight)were all lower in CNGCs silenced plants compared with the wild type plants.Conclusion Significant reduction in antioxidant content and negative effects of physiological and morphological characters in CNGCs silenced plants has revealed the novel role of CNGC genes in enhancing cell integrity under abiotic stress conditions.These results provide vital information that will expand our understanding of the CNGC gene family in cotton and other plants,thus promoting the integration of these genes in the development of the environmental resilient plants.

Apical meristem transcriptome analysis identifies a role for the blue light receptor gene GhFKF1 in cotton architecture development

Cotton architecture is determined by the differentiation fate transition of axillary meristem(AM),and influences cotton yield and the efficiency of mechanized harvesting.We observed that the initiation of flowering primordium was earlier in early-maturing than that in late-maturing cultivars during the differentiation and development of AM.The RNA-Seq and expression level analyses showed that genes FLAVIN BINDING,KELCH REPEAT,F-BOX1(GhFKF1),and GIGANTEA(GhGI)were in response to circadian rhythms,and involved in the regulation of cotton flowering.The gene structure,predicted protein structure,and motif content analyses showed that in Arabidopsis,cotton,rapseed,and soybean,proteins GhFKF1 and GhGI were functionally conserved and share evolutionary origins.Compared to the wild type,in GhFKF1 mutants that were created by the CRISPR/Cas9 system,the initiation of branch primordium was inhibited.Conversely,the knocking out of GhGI increased the number of AM differentiating into flower primordium,and there were much more lateral branch differentiation and development.Besides,we investigated that proteins GhFKF1 and GhGI can interact with each other.These results suggest that GhFKF1 and GhGI are key regulators of cotton architecture development,and may collaborate to regulate the differentiation fate transition of AM,ultimately influencing plant architecture.We describe a strategy for using the CRISPR/Cas9 system to increase cotton adaptation and productivity by optimizing plant architecture.

Effects of planting patterns on yield, quality, and defoliation in machine-harvested cotton

The aim of this study was to elucidate the effects of different machine-harvested cotton-planting patterns on defoliation,yield,and fiber quality in cotton and to provide support for improving the quality of machine-harvested cotton.In the 2015 and 2016 growing seasons,the Xinluzao 45(XLZ45)and Xinluzao 62(XLZ62)cultivars,which are primarily cultivated in northern Xinjiang,were used as study materials.Conventional wide-narrow row(WNR),wide and ultra-narrow row(UNR),wide-row spacing with high density(HWR),and wide-row spacing with low density(LWR)planting patterns were used to assess the effects of planting patterns on defoliation,yield,and fiber quality.Compared with WNR,the seed cotton yields were significantly decreased by 2.06–5.48%for UNR and by 2.50–6.99%for LWR,respectively.The main cause of reduced yield was a reduction in bolls per unit area.The variation in HWR yield was–1.07–1.07%with reduced bolls per unit area and increased boll weight,thus demonstrating stable production.In terms of fiber quality indicators,the planting patterns only showed significant effects on the micronaire value,with wide-row spacing patterns showing an increase in the micronaire values.The defoliation and boll-opening results showed that the number of leaves and dried leaves in HWR was the lowest among the four planting patterns.Prior to the application of defoliating agent and before machine-harvesting,the numbers of leaves per individual plant in HWR were decreased by 14.45 and 25.00%on average,respectively,compared with WNR,while the number of leaves per unit area was decreased by 27.44 and 36.21%on average,respectively.The rates of boll-opening and defoliation in HWR were the highest.Specifically,the boll-opening rate before defoliation and machine-harvesting in HWR was 44.54 and 5.94%higher on average than in WNR,while the defoliation rate prior to machine-harvesting was 3.45%higher on average than in WNR.The numbers of ineffective defoliated leaves and leaf trash in HWR were the lowest,decreased by 33.40 and 32.43%,respectively,compared with WNR.In conclusion,the HWR planting pattern is associated with a high and stable yield,does not affect fiber quality,promotes early maturation,and can effectively decrease the amount of leaf trash in machine-picked seed cotton,and thus its use is able to improve the quality of machine-harvested cotton.

Development of a core set of SNP markers for the identifi cation of upland cotton cultivars in China

Considering the advantages of single nucleotide polymorphisms（SNP） in genotyping and variety identification, the first set public SNP markers at Cotton Marker Database（http：//www.cottonmarker.org/） were validated and screened across standard varieties of cotton distinctness, uniformity and stability（DUS） test, aiming to obtain an appropriate set of core SNP markers suitable for upland cotton cultivars in China. A total of 399 out of 1 005 SNPs from 270 loci including 170 insertions-deletions（In Dels） were evaluated for their polymorphisms among 30 standard varieties using Sanger sequencing. As a result, 147 loci were sequenced successfully, 377 SNPs and 49 In Dels markers were obtained. Among the 377 SNP markers, 333 markers（88.3%） were polymorphic between Gossypium hirsutum and G. barbadense, while 164 markers（43.5%） were polymorphic within upland cotton. As for In Del markers, the polymorphic rate is relatively lower than that of SNP both between species and within species. The homozygous DNA locus ratio of 121 SNPs was higher than 86.2% while that of other 43 SNPs was less than 70%. Only 64 SNPs displayed completely homozygous genotypes among all of the detected upland cotton varieties with 100% homozygous DNA locus ratio. At last, a set of 23 pairs of core SNPs were achieved in view of avoidance of linkage, with polymorphism information content（PIC） values varying from 0.21 to 0.38 with an average of 0.28. Genotype characteristics and genetic diversity were analyzed based on the set of core markers, while 40 pairs of core simple-sequence repeats（SSR） primers comprised of 10 sets of four multiplex PCR combinations were also used for analysis based on fluorescence detection system. Comparison results indicated that the genetic diversity level was almost equal, while various varieties were significantly different from each other. Genetic relationship revealed by SSR markers is related to geographic source to a certain extent. Meanwhile clustering results analyzed by SNP markers are more consistent with kinship, which demonstrated that the screen strategy for core SNP marker is effective.

Effects of soil salinity on rhizosphere soil microbes in transgenic Bt cotton fields

With increased cultivation of transgenic Bacillus thuringiensis （Bt） cotton in the saline alkaline soil of China, assessments of transgenic crop biosafety have focused on the effects of soil salinity on rhizosphere microbes and Bt protein residues. In 2013 and 2014, investigations were conducted on the rhizosphere microbial biomass, soil enzyme activities and Bt protein contents of the soil under transgenic Bt cotton （variety GK19） and its parental non-transgenic cotton （Simian 3） cultivated at various salinity levels （1.15, 6.00 and 11.46 dS m-1）. Under soil salinity stress, trace amounts of Bt proteins were ob- served in the Bt cotton GK19 rhizosphere soil, although the protein content increased with cotton growth and increased soil salinity levels. The populations of slight halophilic bacteria, phosphate solubilizing bacteria, ammonifying bacteria, nitrifying bacteria and denitrifying bacteria decreased with increased soil salinity in the Bt and non-Bt cotton rhizosphere soil, and the microbial biomass carbon, microbial respiration and soil catalase, urease and alkaline phosphatase activity also decreased. Correlation analyses showed that the increased Bt protein content in the Bt cotton rhizosphere soil may have been caused by the slower decomposition of soil microorganisms, which suggests that salinity was the main factor influencing the relevant activities of the soil microorganisms and indicates that Bt proteins had no clear adverse effects on the soil microorganisms. The results of this study may provide a theoretical basis for risk assessments of genetically modified cotton in saline alkaline soil.

The biotypes and host shifts of cotton-melon aphids Aphis gossypii in northern China

Aphis gossypfi is a globally distributed species and therefore has a highly variable life cycle. Populations of A. gossypii in northern China exhibit greater genotypic diversity and a broader host range, yet the details of life cycles of different biotypes is still unclear. In this study, the Cytb and 16S gene regions of A. gossypfi collected from 5 common summer hosts and 4 primary hosts were analyzed. A total of 57 haplotypes were obtained from 1 046 individual A. gossyp# sequences. The sequence included 44 variable sites, 27 of which were parsimony informative sites and 17 of which were singleton variable sites. The most frequent 3 haplotypes were found in 896 individuals, representing a total of 85.7% of all individuals and 36 haplotypes were found in 1 individual. A neighbor-joining tree was constructed using 21 haplotypes that were found in more than 2 individuals. Considering the individual host plant, 5 biotypes were identified. Type 1 corresponded exactly to the cucurbit host-race and the other 4 biotypes were found as cotton host-races. Type 3 was the most abundant biotype in cotton fields in northern China.

Mechanism of floral scent production in Osmanthus fragrans and the production and regulation of its key floral constituents,β-ionone and linalool

Sweet osmanthus(Osmanthus fragrans Lour.)is among the top ten most well-known flowers in China and is recognized as both an aromatic plant and ornamental flower.Here,manual sectioning,scanning electron microscopy,and transmission electron microscopy of sweet osmanthus petals revealed that large amounts of lipids are present inside the petal cells and on the cell surfaces.However,no secretory structures were observed.Instead,the petal cells protrude slightly outward,and the surfaces of the cells are adorned with highly regular brush-shaped hairs.The surfaces of the‘Yingui’petals possessed mostly curled and more numerous hairs,whereas the‘Dangui’petals possessed fewer brush-shaped and more sparsely arranged hairs.In addition,many granular substances were attached to the brush-shaped hairs,and the granules were denser on the hairs of the‘Yingui’petals compared to the hairs on the‘Dangui’petals.Furthermore,35 aromatic components in the‘Yingui’petals and 30 aromatic components in the‘Dangui’petals were detected via GC-MS.The main aromatic component of the‘Yingui’petals wasβ-ionone,whereas that of the‘Dangui’petals was linalool and its oxides.Transcriptome sequencing and qRT-PCR indicated that the highβ-ionone content in the‘Yingui’petals was due to the overexpression of CCD1 and CCD4 and that the high linalool content in the‘Dangui’petals was due to the overexpression of MECS,HDR,IDI1,and LIS1,which function upstream of the linalool synthetic pathway.In particular,the expression levels of CCD4 and LIS1 were upregulated by 5.5-and 5.1-fold in the‘Yingui’and‘Dangui’petals,respectively.One transcription factor(ERF61)was cloned and named,and the expression pattern of ERF61 in sweet osmanthus petals was found to be generally consistent with that of CCD4.Tobacco transformation experiments,yeast one-hybrid experiments,and electrophoretic mobility shift assays indicated that ERF61 binds to the CCD4 promoter and stimulates CCD4 expression,thereby regulating the synthesis ofβ-ionone in sweet osmanthus petals.

Cotton cultivation technology with Chinese characteristics has driven the 70-year development of cotton production in China

Since the founding of the People’s Republic of China in 1949,significant achievements have been made in cotton production in China.China has maintained its position as the world’s largest cotton producer for 33 years(1983–2015),with average annual increases of 3.5 and 3.9% in the unit yield and total output of cotton,respectively.Cotton production has played an extremely important role in the development of the national economy and the improvement of living standards.Although the cotton planting area has been reduced in recent years,the total output has remained relatively unchanged due to the continuous increase in the unit yield.China’s dominant position in global cotton production is undoubtedly attributed to the progress and development of cotton cultivation technology.Over the past 70 years,China has established a high-yielding and high-efficiency cotton cultivation mode that corresponds to its national conditions,including a large population and a limited land area.Furthermore,cotton cultivation technology is constantly being innovated and developed to keep pace with the times.In this paper,we review the development of cotton production and cultivation in China over the past 70 years,with a particular focus on the innovation and development of cotton cultivation technology with Chinese characteristics.This review is intended to provide guidance for the sustainable development of China’s cotton production in the future and to provide a reference for global cotton production.

Identification and expression analysis of group Ⅲ WRKY transcription factors in cotton

The WRKY proteins constitute a large family of transcription factors in plants containing highly conserved WRKYGQK sequences and zinc-finger-like motifs. To comprehensively study WRKY III genes in cotton, we analyzed the genome sequences of Gossypium hirsutum, G. raimondii and G. arboreum. According to the three genome sequences, 18 group III Gh WRKY genes were identified in G. hirsutum, 12 both in G. raimondii and G. arboreum. Phylogenetic and motif analysis showed that proteins with high similarities could be clustered together and had the same motif components. The ratios of non-synonymous（Ka） to synonymous（Ks） of the Gh WRKY to Gr WRKY or Ga WRKY were lower than 1, which indicated that group III WRKY genes in Gossypium species are under purifying selection. Expression analysis revealed that group III Gh WRKY genes expressed during fiber development and leaf senescence, and most of them could be induced by salicylic acid（SA）, jasmonic acid（JA）, ethylene, abscisic acid（ABA）, mannitol, and Na Cl both in roots and cotyledons. Our study gives a briefly introduction on cotton group III WRKY genes and implicates their potential function in cotton fiber development, leaf senescence and abiotic stresses.

Effects of plant density on cotton yield components and quality

Yield and ifber quality of cotton even varies within locules in a bol, but it is not clear how yield components and quality parameters are altered across seed positions of a locule （SPL）. A ifeld experiment was arranged in a split plot design with transgenic insect resistant Bt （Bacilus thuringiensis） cotton hybrid cultivar CRI75 and conventional cultivar SCRC28 as the main plots, and three plant densities （15000, 51000 and 87000 plants ha–1） as the subplots in 2012 and 2013 at Anyang, Henan Province, China. Cotton was hand harvested by node and fruiting position, and then seeds of the ifrst fruiting posi-tion bols from nodes 6–10 were separated by SPL. The effects of plant density on lint yield, ifber quality, especialy across SPL were determined. It was showed that plant densities of 51000 and 87000 plants ha–1 increased lint yield by 61.3 and 65.3% in 2012 and 17.8 and 15.5% in 2013 relative to low plant density （15000 plants ha–1）, however, no signiifcant differ-ence was observed between 51000 and 87000 plants ha–1. The number of bols （bol density） increased while bol weight decreased as plant density raised, and no signiifcant changes occured in lint percentage in 2013 but increased with plant density in 2012. The number of bols in upper nodes and distal fruiting positions, the number of seeds per bol, seed area （SA） and seed vigor index increased with decreasing plant density. Seed area was found to be greater from the base to the middle compared to the apex of a locule. Mote frequency （MF） increased as plant density increased, and ifber quality was the best at the middle of the locule regardless of plant density. As the number of ifbers per seed area is geneticaly determined, adjusting plant density to produce more seeds and greater seed area can be a potentialy promising alternative to improve lint yield in cotton. These ifndings might be of great importantance to cotton breeding and ifled management.

The cotton mitochondrial chimeric gene orf610a causes male sterility by disturbing the dynamic balance of ATP synthesis and ROS burst

Plant cytoplasmic male sterility(CMS)is maternally inherited and often manifested as aborted pollen development,but the molecular basis of abortion remains to be identified.To facilitate an investigation of CMS in cotton,the complete sequence of cotton mitochondrial(mt)genome for CMS-D2 line ZBA was determined.The mt genome was assembled as a single circular molecule with 634,036 bp in length.A total of 194 ORFs,36 protein-coding genes,six r RNAs,and 24 t RNAs were identified.Several chimeric genes encoding hypothetical proteins with transmembrane domains were identified.Among them,a previously unknown chimeric gene,orf610a,which is composed of atp1 and a 485-bp downstream sequence of unknown nature,was identified.RT-PCR and q RT-PCR validation indicated that orf610a was expressed specifically in a sterile line.Ectopic expression of orf610a in yeast resulted in excessive accumulation of reactive oxygen species and reduction in ATP content,in addition to inhibition of cellular growth.Transgenic A.thaliana overexpressing orf610a fused with a mitochondrial targeting peptide displayed partial male sterility.Interaction between ORF610a and the nuclear-encoded protein RD22 indicated an association between ORF610a and pollen abortion.Positive feedback during transcriptional regulation between nuclear regulatory factors and the mt CMS gene may account for the male sterility of ZBA.

Genetic Analysis of Earliness Traits in Short Season Cotton (Gossypium hirsutum L.)

Inheritance and interrelationship of phenotype and genotype of earliness traits were evaluated in a diallel analysis involving six early-maturing parents. Date of first square （DFS）, date of first flower （DFF）, date of first open boll （DFOB）, number of node first sympodial branch （NNFSB）, and harvested rate before frost （HRBF） as earliness traits of six parents, 15 F1 hybrids and 15 F2 progenies were investigated from 2005 to 2008. The experiment design was a randomized complete block design with three replications. Additive, dominance and epistasis effects were analyzed with ADAA （additive- dominance-epistasis） model. HRBF, DFF, and DFOB showed significant additive genetic variances. Heritability estimates ranged from 0.088 （HN, narrow sense） and 0.416 （HNE, environment interaction） for HRBF, to 0.103 （HN） and 0.524 （HNE） for DFF, and to 0.187 （HN） and 0.519 （H~） for DFOB. Dominance genetic effects for DFS, DFF, DFOB, and NNSFB were stronger than additive effects. Additive-by-additive epistatic effects for DFS, DFOB, and NNSFB were detected and affected by environment. Correlation analysis showed generally that HRBF had a significant negative genetic and phenotypic correlation with DFS, DFOB, and NNFSB; DFS had significant positive genetic and phenotypic correlations with DFF, DFOB, and NNFSB; significant positive genetic and phenotypic correlations were also detected between DFF and DFOB, DFF and NNFSB, DFOB and NNFSB. The results showed that the lower the node to the first fruiting branch and the shorter the plant, the earlier was the onset of squaring, flowering, and boll opening, the higher was the harvest rate before frost. Heredity of earliness traits among parents and their hybrids were also detected and parents A1, A2, Bl, B2, and B3 could be used to improve earliness traits of short season cotton cultivars.

Genetic structure,gene flow pattern,and association analysis of superior germplasm resources in domesticated upland cotton(Gossypium hirsutum L.)

Gene flow patterns and the genetic structure of domesticated crops like cotton are not well understood.Furthermore,marker-assisted breeding of cotton has lagged far behind that of other major crops because the loci associated with cotton traits such as fiber yield and quality have scarcely been identified.In this study,we used 19 microsatellites to first determine the population genetic structure and patterns of gene flow of superior germplasm resources in upland cotton.We then used association analysis to identify which markers were associated with 15 agronomic traits(including ten yield and five fiber quality traits).The results showed that the upland cotton accessions have low levels of genetic diversity(polymorphism information content=0.427),although extensive gene flow occurred among different ecological and geographic regions.Bayesian clustering analysis indicated that the cotton resources used in this study did not belong to obvious geographic populations,which may be the consequence of a single source of domestication followed by frequent genetic introgression mediated by human transference.A total of 82 maker-trait associations were examined in association analysis and the related ratios for phenotypic variations ranged from 3.04% to 47.14%.Interestingly,nine SSR markers were detected in more than one environmental condition.In addition,14 SSR markers were co-associated with two or more different traits.It was noteworthy that NAU4860 and NAU5077 markers detected at least in two environments were simultaneously associated with three fiber quality traits(uniformity index,specific breaking strength and micronaire value).In conclusion,these findings provide new insights into the population structure and genetic exchange pattern of cultivated cotton accessions.The quantitative trait loci of domesticated cotton identified will also be very useful for improvement of yield and fiber quality of cotton in molecular breeding programs.

Estimating light interception using the color attributes of digital images of cotton canopies

Crop growth and yield depend on canopy light interception （LI）. To identify a low-cost and relatively efficient index for measuring LI, several color attributes of red-green-blue （RGB）, hue-saturation-intensity （HSI）, hue-saturation-value （HSV） color models and the component values of color attributes in the RGB color model were investigated using digital images at six cotton plant population densities in 2012-2014. The results showed that the LI values followed downward quadratic curves after planting. The red （R）, green （G） and blue （B） values varied greatly over the years, in accordance with Cai＇s research demonstrating that the RGB model is affected by outside light. Quadratic curves were fit to these color attributes at six plant population densities. Additionally, linear regressions of LI on every color attribute revealed that the hue （H） values in HSI and HSV were significantly linearly correlated with LI with a determination coefficient （R2）〉0.89 and a root mean square error （RMSE）=0.05. Thus, the H values in the HSI and HSV models could be used to measure LI, and this hypothesis was validated. The H values are new indexes for quantitatively estimating the LI of heterogeneous crop cano- pies, which will provide a theoretical basis for optimizing the crop canopy structure. However, further research should be conducted in other crops and under other growing and environmental conditions to verify this finding.

Early ABA-stimulated maintenance of Cl^(−) homeostasis by mepiquat chloride priming confers salt tolerance in cotton seeds

Mepiquat chloride(MC)priming alleviates the effects of salt stress during seed germination in cotton(Gossypium hirsutum L.),but the mechanisms underlying its effects are unknown.We found that MC priming increases salt tolerance,as evidenced by marked increases in seed vigor and germination rates,and alleviated salt toxicity by reducing Cl^(−)accumulation in germinating seeds.Consistently,electrophysiological experiments revealed that the seeds with MC priming displayed superior Cl^(−)exclusion ability in the root apex.These beneficial effects of MC priming were abolished by the abscisic acid(ABA)-synthesis blocker fluridone under salt stress.MC priming induced an early response to acclimatization and stress,as indicated by rapidly increasing ABA content during initial exposure to salt stress.Transcriptome analyses revealed that MC priming induced an array of differentially expressed genes(DEGs)in germinating seeds.The most noticeable changes in germinating seeds were MC priming-induced increases in the expression of DEGs encoding components of ABA biosynthesis,ABA catabolism,and ABA signaling pathways under salt stress.MC priming also increased the expression of some DEGs encoding Cl^(−)ion transporters(e.g.CCC,SLAC1/SLAH1/SLAH3,CLC,and ALMT9)in germinating seeds.These results indicate that MC priming-induced ABA contributes to Cl^(−)homeostasis in tissues and acts as a positive regulator of salt tolerance via regulation of Cl^(−)transporters(particularly CCC and SLAC1/SLAH1/SLAH3).Taken together,these findings shed light on the molecular mechanism underlying MC-mediated tolerance to salt stress during seed germination.

A review of the pathogenicity mechanism of Verticillium dahliae in cotton

Verticillium wilt,caused by the notorious fungal pathogen Verticillium dahliae,is one of the main limiting factors for cotton production.Due to the stable dormant structure microsclerotia,long-term variability and co-evolution with host plant,its pathogenicity mechanism is very complicated,and the interaction mechanism between pathogen and host plant is also unclear.So identification and functional analysis of the genes involved in the pathogenicity or virulence of this fungus will benefit to uncover the molecular pathogenic mechanism of V.dahliae.In this review,many multifunction genes covering microsclerotia development,pathogen infection,effector proteins,transcription factors,horizontal gene transfer and trans-kingdom RNA silencing have been summarized to provide a theoretical basis to deep understand the molecular pathogenicity mechanism of V.dahliae and promote to effectively control Verticillium wilt.Furtherly,these pathogenicity-related genes may be considered as targets for effective control of Verticillium wilt in cotton.

Efficacy evaluation and mechanism of Bacillus subtilis EBS03 against cotton Verticillium wilt

Background:In our previous study,a strain EBS03 with good biocontrol potential was screened out of 48 strains of cotton endophyte Bacillus subtilis by evaluating the controlling effect against cotton Verticillium wilt.However,its mechanism for controlling Verticillium wilt remains unclear.The objective of this study was to further clarify its con-trolling effect and mechanism against cotton Verticillium wilt.Results:The results of confrontation culture test and double buckle culture test showed that the inhibitory effects of EBS03 volatile and nonvolatile metabolite on mycelium growth of Verticillium dahliae were 70.03%and 59.00%,respectively;the inhibitory effects of sporulation and microsclerotia germination were 47.16%and 70.06%,respec-tively.In the greenhouse test,the EBS03 fermentation broth root irrigation had the highest controlling effect at 87.11%on cotton Verticillium wilt,and significantly promoted the growth of cotton seedlings.In the field experi-ment,the controlling effect of EBS03 fermentation broth to cotton Verticillium wilt was 42.54%at 60 days after cotton sowing,and the boll number per plant and boll weight in EBS03 fermentation broth seed soaking,root irrigation,and spraying treatments significantly increased by 19.48%and 7.42%,30.90%and 2.62%,15.99%and 9.20%,respec-tively.Furthermore,EBS03 improved the resistance of cotton leaves against the infection of V.dahliae,and induced the outbreak of reactive oxygen species and accumulation of callose.In addition,the results of real time fluorescent quantitative polymerase chain reaction(RT-qPCR)detection showed that EBS03 significantly induced upregulation expression level of defense-related genes PAL,POD,PPO,and PR10 in cotton leaves,enhanced cotton plant resistance to V.dahliae,and inhibited colonization level of this fungal pathogen in cotton.Conclusion:Bacillus subtilis EBS03 has a good biological defense capability,which can inhibit the growth and coloni-zation level of V.dahliae,and activate the resistance of cotton to Verticillium wilt,thus increase cotton yield.