| Chemical capping is a new capping method that uses plant growth regulators to inhibit cell division and elongation,thereby delaying and controlling the growth of cotton tips.It has the characteristics of low cost,high efficiency and short time consuming.In order to understand the effects of different chemical capping agents on cotton fields in southern Xinjiang,5 kinds of chemical capping agents were selected: 25%fluconamide suspension agent(X1),3% 14-hydroxyrutinyl uniconazole suspension agent(X2),22.5% 28-epianopyrium water agent(X3),50% chlormequat water agent(X4),and 250 g/L meperidium water agent(X5),with artificial topping as control(CK),to study its effects on cotton growth and development,leaf boll spatial configuration,population photosynthetic characteristics,canopy structure and light distribution,protective enzymes,yield formation and quality characters,elucidate the high-yield mechanism of cotton under different chemical capping agents,and provide reference for the cultivation and management technology of cotton in southern Xinjiang.The main conclusions are as follows:(1)Effects on cotton growth and development: Compared with CK,the plant width of ’Xinluzhong 67’and ’Tahe No.2’ decreased by 4.01～9.08 cm and 4.92～10.76 cm,respectively.Both varieties had the best capping and shaping effect with X5 treatment,with an average increase of 0.90 cm,0.78 nodes,and 1.32 sets in plant height,main stem nodes,and fruit tables compared with CK,and an average decrease of 3.07 pieces and 3.85 nodes in total green leaves and total fruit nodes compared with CK;Compared with CK,the plant height,main stem nodes,and fruit nodes of X3 treatment increased by 2.25 cm,1.53 nodes,and1.98 nodes on average,while the total number of green leaves and total fruit nodes decreased by 1.55 pieces and 2.56 nodes on average,with the second highest capping effect;The number of green leaves,fruit sets,and plant height of X1 and X2 treatments significantly increased compared to CK,and the capping effect was poor.In the treatment with capping agent,the total number of green leaves of ’Xinluzhong 67’was greater than that of ’Tahe 2’,while its plant height,number of main stem nodes,number of fruit tables,and total number of fruit nodes were smaller than that of ’Tahe 2’.(2)Effects on spatial arrangement of leaf boll of cotton: Spraying capping agent significantly inhibited the growth of the upper functional leaf width and the last five fruit branches of cotton,and X5 treatment had the greatest inhibitory effect.X2,X3,and X5 treatments had a large number of upper bolls,ranging from 2.52 to 2.90,with the largest number of middle bolls in X5 treatment.There was no significant difference in the number of lower bolls among various treatments.The cotton boll abscission rate in the upper part of X3 and CK treatments was the lowest,60.87% and 61.45%,respectively;In the middle,X5 and CK treatments were the smallest,66.22% and 65.17% respectively;The treatment of X3 and CK in the lower part was the smallest,60.87% and 61.45% respectively.The boll abscission rate in the inner circumference of cotton plant was the lowest in treatments X1 and X5,followed by treatments X3 and CK,and the highest in treatments X2 and X4;The cotton boll abscission rate of each treatment was relatively high.(3)Effects on photosynthetic characteristics of cotton population: The average final SPAD values for the upper and middle parts of each capping agent treatment were 59.06 and 62.40 for ’Xinluzhong 67’,respectively,increasing by 0.91% and 0.84% compared to CK,and 64.61 and 65.02 for ’Tahe 2’,respectively,increasing by 1.03% and 2.10% compared to CK.The lower part is opposite to the upper and middle parts,and its average SPAD value is smaller than that of manual topping during the same period.Among them,the X3 and X5 treatments of ’Xinluzhong 67’ and the X3 and X2 treatments of ’Tahe 2’ have little difference from CK.Both varieties were treated with X3 and X5,and the Pn,Gs,and Tr reached the peak value and were significantly higher than CK 10 to 20 days after application,while Ci was negatively correlated with Pn.The treatment with X5 reached the minimum value and was significantly lower than CK10 days after application.(4)Effects on cotton canopy structure and light distribution: The leaf area index(LAI)in the upper and middle parts of cotton canopy in southern Xinjiang showed a trend of first increasing and then decreasing after application,while the LAI in the lower part showed a continuous downward trend.Spraying capping agent significantly increased the canopy LAI,mean leaf inclination angle(MTA),and non intercepted scattering(DIFN),with the average LAI,MTA,and DIFN increased by 20.31%,2.52%,and 43.25%compared to CK,respectively.The upper light transmittance of each capping treatment significantly increased,with X1,X3,and X5 treatments having the highest upper light transmittance,which was beneficial for the middle and lower parts of the canopy to receive light.(5)Effects on leaf protective enzymes: The average POD,CAT activity,and MDA content of capping treatment,for ’Xinluzhong 67’,were 392.30 Δ OD470/(min · g),61.82 U/g FW/min and 36.02 μ Mol/g FW,respectively,increased by 21.06%,1.83%,and 13.64% compared to CK,respectively,for ’Tahe 2’,were470.85 Δ OD470/(min · g),73.68 U/g FW/min and 29.37 μ Mol/g FW respectively,increased by 11.38%,3.41% and 6.41% compared to CK,respectively.The average SOD activity of ’Xinluzhong 67’ was 412.06U/g FW,which was 15.82% lower than CK,’Tahe 2’ was 469.70 U/g FW,which was 12.35% lower than CK;The enzyme activities of leaves treated with X3,X4,and X5 were higher in all capping agent treatments,and the average CV of enzyme activities of ’Xinluzhong 67’ was 7.0%,higher than 5.97% of’Tahe 2’.(6)Influence on yield formation: Compared with manual topping,the X3 and X5 treatments of’Xinluzhong 67’ had more bolls per plant,with a 2.86% and 4.90% increase in seed cotton yield.The X5 treatment of ’Tahe 2’ had the most bolls per plant,with a 3.26% increase in seed cotton yield.The CV of bolls per plant,total bolls,weight per boll,and yield of ’Xinluzhong 67’ were 11.58%,13.14%,5.46%,and14.30%,respectively,which were 27.35%,26.53%,66.05%,and 9.58% higher than those of ’Tahe 2’,indicating that the sensitivity of yield components of ’Xinluzhong 67’ to different capping agent treatments was higher than that of ’Tahe 2’.Conclusion: Spraying capping agent can control plant height,inhibit plant width,increase photosynthetic performance of leaves,and play a role in shaping and increasing bolls.Different varieties have different sensitivities to capping agents,and ’Xinluzhong 67’ is more sensitive to capping agents than ’Tahe 2’.The application of 250 g/L methylpiperidine water agent and 22.5% 28 epinephridine water agent to’Xinluzhong 67’ in the southern Xinjiang cotton region,and the application of 250 g/L methylpiperidine water agent to ’Tahe 2’ has the best effect on capping and stabilizing production,which can be used for reference in production practice. |
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