| Cotton textile industry plays an important role in the development of national economy of China,in which cotton is widely cultivated.In recent years,mechanization of cotton production is urgently required because of continuous increasing of labor cost.In order to adapt to the high density cultivation of machine mining mode,new cotton varieties must be better on ventilation,light transmission and high photosynthetic efficiency.Leaf is not only the most important photosynthetic organ,but also an important factor affecting canopy structure of cotton.At present,most of the varieties popularized are types with normal leaf shape.Under the condition of high-density planting,canopy can be depressed easily,which affects the yield and quality of cotton.With a deeper leaf lobe length,sub-okra leaf shape exhibits advangtage in the improvement of cotton canopy structure.In this paper,effect of sub-okra leaf shape on photosynthetic physiological characteristics,canopy structure,yield and fiber quality was studied,as well as the response to drought stress.The chromosal location of gene controlling sub-okra leaf shape was mapped finely,and the function of its alleles was also analyzed.Based on the polymorphism of promoter sequence,specific markers were developed for each allele.The results are as follows:1.With a deeper leaf lobe length and moderate leaf area coefficient,sub-okra leaf shape could optimize canopy structure of cotton.Compared with normal leaf,sub-okra leaf could improve canopy structure by significantly increasing leaf lobe length,and reducing leaf lobe width and leaf area.The measurement of leaf area coefficient and light transmittance showed that leaf area coefficient of sub-okra leaf was slightly smaller than that of normal leaf,while the light transmittance was higher than that of normal leaf.Although okra leaf had more deeper leaf lobe length,smaller leaf lobe width and better canopy transmittance than sub-okra leaf,its leaf area coefficient was too small to produce high biomass.2.Sub-okra leaf germplasm had higher photosynthetic rate and lower chlorophyll content,which could improve photosynthetic physiological characteristics and increase yield of cotton.Under genetic backgrounds of LMY 22 and LMY 28,the net photosynthetic rate of sub-okra leaf was higher than that of normal leaf and okra leaf,and the chlorophyll content was slightly lower than that of normal leaf and okra leaf.3.Sub-okra leaf shape could increase biomass and yield of fiber,and had no negative effect on fiber quality.Under the planting mode of 76 cm and 75000 plants / Ha,the final biomass of lines with sub-okra leaf was 4.3% and 33.4% higher than that of lines with normal leaf,respectively.Yield was also increased by 7.69% and 9.29% in lines with sub-okra leaf,respectively.Some indexes of fiber quality were slightly improved in lines with sub-okra leaf shape,but there was no significant difference.4.The drought tolerance of lines with sub-okra leaf was better than that of normal leaf.Under stress of 15% PEG,the response to drought sress was significantly different between lines with sub-okra leaf and lines with normal leaf.The transpiration rate(TR),stomatal conductance(GS),net photosynthetic rate(PN),i Intercellular carbon dioxide concentration(CI),chlorophyll content and Fv / FM of sub-okra leaf were better than those of normal leaf after stress and rehydration.The activity of SOD,POD,CAT,APX and the contents of osmolytes(soluble sugar and proline)in sub-okra leaf were also higher than that in normal leaf.5.The sub-okra leaf gene was fine-mapped on chr15.It was found that this gene and its alleles had significant dose effect on regulation of leaf shape development.It was found that sub-okra leaf gene was located on chromosome 15 through gene fine mapping.The function of this gene and its alleles was analyzed by VIGS.It was found that the expression of alleles were significantly down regulated,and the ratio of the main lobe length was significantly reduced in super okra leaf,okra leaf and sub-okra leaf,in which the leaf phenotypes changed to okra leaf,sub-okra leaf and normal leaf,respectively.An obvious dose effect was exhibited.6.According to the polymorphic sites in promoter of sub-okra leaf gene,specific molecular markers were designed to distinguish sub-okra leaf with its alleles.A total of 26 polymorphic loci were identified from the promoter region of four alleles.Based on one In Del and four SNP loci,specific molecular markers were designed to distinguish alleles,among which CAPS＿689was specific marker for sub-okra leaf gene,d CAPS＿519、d CAPS＿192 and CAPS＿166 were specific marker for super okra leaf,okra leaf and normal leaf gene,respectively.These specific molecular markers could be used to identify different leaf shapes.In this study,it was found that sub-okra leaf germplasm was a high light efficiency germplasm with drought resistance.The relatively deep leaf lobe length,narrow leaf lobes could optimize the canopy structure and improve the light transmittance of middle and lower canopy.The suitable leaf area coefficient and higher net photosynthetic rate ensure the ability of dry matter synthesis,which lays a foundation for the increase of production.At the same time,they also show better adaptability to drought stress.Sub-okra leaf had a faster response to drought stress.With VIGS,we found that sub-okra leaf gene and its alleles have obvious dose effect on the regulation of leaf shape,and the difference of promoter region might be the key to the regulation of different leaf shape.The results of this study could provide theoretical support for application of sub-okra leaf germplasm in development of new cotton varieties suitable for mechanical harvesting and drought tolerance in the Yellow River Basin,and also lay foundation for the study of the molecular mechanism of high light efficiency and drought tolerance of sub-okra leaf germplasm. |
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