| 【Objective】Cotton is one of the important economic crops in the world.China is the world’s largest cotton consumer and textile exporter.Xinjiang,as the country’s largest cotton producing area,not only provides a strong guarantee for the huge domestic cotton demand,but also promotes economic development and farmers’ income in Xinjiang.With the continuous advancement of cotton production mechanization and the continuous expansion of machine-picked cotton area,mechanical harvesting has become the main method of current cotton harvesting.The lodging resistance of cotton directly affects the machine-picking effect of cotton.Lodging-resistant strains can easily enter the picking head for fiber picking.The lodging stems make it difficult for part cotton fibers to enter the picking head,thereby affecting the net harvest rate and reducing cotton yield and quality.Additionally,the cotton picker rolls down the lodging cotton to reduce the fiber quality.At present,there are still few studies on the cotton lodging resistance related morphological and physiological characteristics.In this study,two types of strains with different lodging-resistant ability were used as materials to compare their difference from morphological,physiological characteristics and gene expression level,which will provide a basis for the cultivation and breeding of lodging-resistant cotton strains.【Methods]】(1)Two lodging-resistant strains(M153 and M4560)and four easily lodging strains(S11,W93,M5326 and M5330)were selected.The experiment adopted a randomized blocks design,and selected three growing stages,including bud stage,boll stage and boll opening stage.(2)Ruler,vernier caliper,electronic balance,and stem strength tester were used to measure the morphological characteristics,such as plant height,stem diameter,internode length,puncture resistance,tensile and flexural strength,and stem fresh weight;The same part of the stalk from different cotton strains was cut to made dyed slices,which was used to observe the dyed area of the cross-section of the stalk,and to determine the degree of lignification and the number of vascular bundles;(3)The kit and the reagents prepared in the laboratory were used to determine the content of lignin,cellulose,soluble sugar,and the four enzyme activities of PAL,4CL,CAD and TAL related to lignin synthesis in cotton stems by spectrophotometry;(4)The stem samples from the lodging-resistant M153 and lodging variety W93 at three growing stages were collected and used for transcriptome sequencing by using the Baimaike cloud platform.【results and conclusions】(1)Morphological characteristics of stalks from cotton strains with different lodging resistance ability Compared with easily lodging cotton strains(S11,W93,M5326 and M5330),the lodging-resistant strains(M153 and M4560)had higher plant height,stem diameter,height of gravity center,length of the second internode,and stem fresh weight,suggesting that stem morphological characteristics are not necessarily related to lodging resistance ability.Dwarf strains are not necessarily lodging resistance,and high stalk strains are not necessarily easy to lodging.Compared with easily lodging cotton strains(S11,W93,M5326 and M5330),the lodging-resistant strains(M153 and M4560)had darker staining in both xylem and phloem and larger staining area,indicating they had a higher degree of lignification and vascular bundles.The results showed that the degree of lignification and the number of vascular bundles in cotton stalks were closely related to lodging resistance ability.The higher the degree of lignification and the greater the number of vascular bundles,the stronger the lodging resistance ability.(2)Stem physiological properties from cotton strains with different lodging resistance ability Compared with easily lodging cotton strains(S11,W93,M5326 and M5330),the lodging-resistant cultivars(M153 and M4560)had significantly higher contents of lignin,cellulose and soluble sugar in the stems,and higher enzymatic activity of PAL,4CL,TAL and CAD related to lignin synthesis.The results showed that the content of lignin,cellulose and soluble sugar and the activities of enzymes related to lignin synthesis in cotton stalks were closely related to lodging resistance traits.These physiological properties can be used as important physiological indexes for screening lodging-resistant cotton strains.(3)Correlation between mechanical and physiological characteristics of cotton stalks With the growth and development of cotton stalks,the correlation between the mechanical characteristics and physiological characteristics of the stalks gradually increased.Compared with puncture resistance index,the correlation between tensile and flexural strength and various physiological indexes was more obvious.The content of lignin,soluble sugar and cellulose and activity of PAL,4CL and CAD enzymes had a significant positive association with tensile and flexural strength at the boll stage and boll-opening stage,indicating that tensile and flexural strength can be used as a key index for screening lodging-resistant cotton strains.(4)Transcriptome analysis of lodging-resistant and easily lodging strains A total of 5718 differentially expressed genes were obtained by comparing the transcriptome data between lodging-resistant and easily lodging strains,of which many lignin(PAL,PAL6,4CL1,CCR1,CAD1,CAD9,COMT1,LAC5,LAC17,PER64 and PRXIIB),cellulose(Csl E1,Csl E6,Cse A4,Cse A7,and Cse A8),starch and sucrose(alg C,BGLU41,AMY2,BMY1,WAXY and SS)synthesis-related genes were screened.Gene expression heat map analysis showed that the expression levels of these genes in the lodging-resistant variety M153 were significantly higher than that in the easily lodging variety M153,which was consistent with the content determination results,indicating that these genes play an important role in the process of cotton lodging resistance,providing a reference for assisted screening lodging-resistant cotton strains from the molecular level. |
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