| Lagerstroemia indica L.belongs to the genus Lagerstroma.It is an important flower shrub or small tree in summer and has been widely cultivated.In all kinds of green space,L.indica is pruned by extremely heavy cutting or heavy cutting in winter,so that its crown shape is mainly formed by the current year branches.L.indica had long,soft branches,large number of flowers and heavy terminal inflorescence,which resulted in loose crown shape and reduced its ornamental value.It is of great significance to improve the ornamental value of L.indica by improving its crown structure.In this study,two L.indica varieties,L.indica’Dahua Zhaolu’and L.indica’Ziyu’,were used as experimental materials.Four plant growth retardants:CCC、PP333、S-3307 and KUH-833 were used to treat the test materials by foliar spraying every 7 days（5 times in total）with four concentration gradients.After spraying,the growth amount every 7 days was calculated by branch length,branch base diameter,branch slim ratio,etc.The lignin content of branches and the activities of related enzymes（POD,PAL,C4H）in lignin synthesis were determined.7 days after the last spraying,the branching Angle,bending resistance,anatomical structure and endogenous hormone content of the first grade branches were measured.Through the evaluation of the experimental results,the optimal treatment scheme was selected to regulate the crown shape of L.indica during the growth period and make its plant shape compact and full.The relevant results of this study are as follows:1.The effects of plant growth retarder on the crown shape of L.indica‘Dahua Zhaolu’:the treatment of CCC can significantly promote the growth and basal diameter of its branches,while the treatment of PP333,S-3307 and KUH-833 can significantly inhibit the growth and basal diameter of its branches.The four plant growth retardants had the same effect on the wispiness ratio,flexure resistance and branch Angle,all of which significantly reduced the wispiness ratio and branch Angle,significantly increased the flexure resistance of branches,and made the branches of tested plants stronger and more compact.2.The effect of plant growth retarder on the crown shape of L.indica‘Ziyu’:the treatment of CCC can promote the branch elongation and growth of L.indica‘Ziyu’,but the difference between the treatment and the control is not significant level,in addition,significantly promote the thickening of the base diameter of its branches.The treatments of PP333,S-3307 and KUH-833 significantly inhibited the elongation and growth of branches,and the basal diameter of branches was significantly decreased when the concentration of S-3307 was 1 500～1 600mg·L-1,while the basal diameter of branches was significantly increased when the concentration of KUH-833 was 600mg·L-1.The influence of other treatment groups on branch base diameter was not significant compared with the control group.All of the four plant growth retards significantly reduced the twig wispiness and branching Angle of L.indica‘Ziyu’,and most of the effects on the bending strength of its branches were increased.However,there were significant differences between the 1 200～1300 mg·L-1PP333 treatment group and the 1 500 mg·L-1S-3307 treatment group and the control.3.The treatment concentration of CCC was 100 mg·L-1,and the treatment concentration of CCC was 150 mg·L-1,and the treatment concentration of CCC was 150mg·L-1,and the control effect of L.indica‘Ziyu’was the best.When the concentration exceeded 200 mg·L-1,irregular yellow spots appeared on the leaf edges of the two L.indica varieties,indicating that the concentration of 200 mg·L-1was close to the tolerance limit of the two L.indica varieties.4.The best regulation effect on the crown shape of L.indica‘Dahua Zhaolu’was obtained when the concentration of PP333 was 1 200 mg·L-1,and the best regulation effect on the crown shape of L.indica‘Ziyu’was obtained when the concentration of PP333 was 1100 mg·L-1.When the concentration of polybulozole was 1 400 mg·L-1,the ABA content in the stem tip of L.indica‘Dahua Zhaolu’significantly increased,and the tested plants appeared the phenomenon of holding flowers,indicating that the concentration of PP333was 1 400mg·L-1and began to produce drug harm to L.indica‘Dahua Zhaolu’5.The best control effect on the coronial shape of L.indica‘Dahua Zhaolu’was obtained when the concentration of S-3307 was 1 500 mg·L-1,and the best control effect on the coronial shape of L.indica‘Ziyu’was obtained when the concentration of S-3307 was1 600mg·L-1.When the concentration of enconazole was between 1 600 and 1 700 mg·L-1,the growth condition of"Dahua Chaolu"L.indica was poor and the leaves were sparse.When the concentration of enconazole was 1 700 mg·L-1,the situation of L.indica‘Ziyu’also appeared,indicating that the concentration of enconazole was 1 600 mg·L-1and began to cause drug harm to L.indica‘Dahua Zhaolu’.The concentration of 1 700 mg·L-1began to produce drug harm to"purple jade"L.indica.6.The best control effect on the crown shape of L.indica‘Dahua Zhaolu’and L.indica‘Ziyu’was achieved when the concentration of KUH-833 was 600 mg·L-1.The lignin content of the branches of the two L.indica varieties was less than that of the control when the concentration of KUH-833 was between 1 000 and 1 200 mg·L-1after five consecutive spraying,and there was little difference in the effect of the concentration range on the length of the branches of the two L.indica varieties in the experiment,indicating that the inhibitory effect of the concentration range on the length of the branches of the two Crme myrtle varieties had reached the limit.7.Membership function analysis was conducted on the indexes of the four plant growth retarder treatment groups against the optimal treatment group of L.indica‘Dahua Zhaolu’.The results showed that 100 mg·L-1CCC treatment group had the highest score,followed by 1 200 mg·L-1PP333 treatment group,and 1 500 mg·L-1S-3307 treatment group.The600 mg·L-1KUH-833 treatment group had the lowest score.In conclusion,100mg·L-1CCC spray treatment was the best treatment plan for the crown regulation effect of L.indica‘Dahua Zhaolu’.8.The membership function analysis of the indexes of the four plant growth retarder treatment groups against the optimal treatment group of L.indica‘Ziyu’.The results showed that the 1 100 mg·L-1PP333 treatment group scored the highest,followed by the150 mg·L-1CCC treatment group,followed by the 1 600 mg·L-1S-3307 treatment group.The 600 mg·L-1KUH-833 treatment group had the lowest score.In summary,the 1 100 mg·L-1polybulozole spray treatment was the best treatment plan for the crown regulation effect of L.indica‘Dahua Zhaolu’.Based on the above analysis,it can be concluded that the regulation effect of CCC and PP333 on the crown shape of the two L.indica varieties is better than that of S-3307 and KUH-833,in which aizhuangxin can increase the current growth of L.indica,while polyphozole can inhibit the current growth of L.indica.The optimum concentration of CCC is less than 200mg·L-1,and the optimum concentration of PP333 is between 1 100 and 1 200 mg·L-1.CCC is lower than PP333 in cost.In addition,for other varieties of L.indica,too-high concentration of CCC treatment only causes the appearance of yellow spots on the leaves,while the concentration of PP333 treatment beyond the tolerance range may cause the phenomenon of flower holding,which has a greater impact on the ornamental value.Therefore,in the production application,it is more recommended to use the CCC-treatment to regulate L.indica crown shape. |
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