Effects Of Growth Regulators On Bud Formation And Early Flowering Of Rhododendron

Rhododendron is a woody plant in Ericaceae.It has a long flowering period.It is mainly used in park green space in southern China,and is mostly planted in the form of flower beds and flower clusters.The flowering period of Rhododendron is concentrated in March to May every year,missing National Day,New Year’s Day,Spring Festival and other festivals,which is difficult to meet people’s viewing needs for park green space at a specific time point.The timely and appropriate spraying of plant growth regulators can promote the flowering of plants.Therefore,this study used the Rhododendron’Miyo-no-Sakae’as the test material,and used growth regulators to regulate the flowering period of Rhododendron.The relationship between plant growth regulators and physiological characteristics such as endogenous hormones and carbohydrates was analyzed in order to provide a theoretical basis for the regulation practice of Rhododendron flowering period,which was of great significance to the practical application and promotion of the regulation technology of Rhododendron flowering period in park greening.The main results were as follows:1.In order to screen suitable growth regulators for Rhododendron flower bud induction,single factor test and factorial test were used to screen the optimal concentration and spraying time of（chloride）CCC and（daminozide）B₉at different stages after flower withering,with four dimensions of flower bud formation rate,flower bud formation time,flower bud formation peak time and flower bud formation duration.The results showed that compared with the control,spraying different concentrations of CCC and B₉at 30 d and 80 d after flowering could induce the early formation of flower buds in different degrees,the rate of flower bud formation increased by 2.45～15.73%,and the time required for flower bud formation was shortened by 14.00～35.50 d.However,there was no significant difference in the peak time and duration of flower bud formation（P>0.05）.Among them CCC and B₉were sprayed on 30 d,and 2000 mg·L^-1CCC treatment was the best.The flower bud formation rate was significantly increased by 15.73%compared with the control,and the time required for flower bud formation was shortened by27.83 d compared with the control.There was no significant difference in the peak time and duration of flower bud formation compared with the control.The treatment of 2000 mg·L^-1CCC had the best effect at 80 d after flowering,the rate of flower bud formation was 10.68%higher than that of the control,the time required for flower bud formation was shortened by 7 d compared with the control,the peak period of flower bud formation was 23 d earlier than that of the control,and the time required for flower bud formation and the duration of flower bud formation were not significantly different from those of the control.Through the comparison of the optimal spraying concentration at different time points,it was found that the time required for flower bud formation at 30 d after flowering was significantly 13.17 d earlier than that at 80 d after flowering,the peak period of flower bud formation was significantly 40.50 d earlier than that at 80 d after flowering,and the duration was significantly 35.50 d earlier.In conclusion,spraying 2000mg·L^-1CCC on 30 d after flowering had the best effect on Rhododendron bud induction.2.Through the determination of physiological indexes such as soluble sugar,starch,soluble protein,photosynthetic pigments and endogenous hormones in leaves during the formation of Rhododendron flower buds induced by 2000 mg·L^-1CCC,the results showed that compared with the control（water）,CCC treatment could significantly increase the contents of soluble sugar,starch,soluble protein,chlorophyll a,chlorophyll b,total chlorophyll and（zeatin）ZT in Rhododendron leaves（P<0.05）,and inhibit the synthesis of（gibberellin）GA₃and（auxin）IAA in Rhododendron leaves（P<0.05）.The ratios of ZT/GA₃,ZT/IAA,ABA/GA₃and ABA/IAA were significantly increased（P<0.05）.It indicated that CCC treatment enhanced the ability of light energy capture and promoted the accumulation of soluble sugar,starch and protein in leaves inducing the early formation of Rhododendron buds;lower GA₃and IAA content and higher ZT/GA₃,ZT/IAA,ABA/GA₃and ABA/IAA ratio were beneficial to induce flower bud formation.3.In order to blossom early,different concentrations of growth promoter GA₃were sprayed at different periods after the formation of flower buds,and the optimal concentration and spraying time of GA₃were screened from seven dimensions:the number of days required for flowering,the initial flowering period,the full flowering period,the final flowering period,the number of days in advance,the flowering period and the flowering rate.the results showed:（1）Compared with the control,the time required for flowering by spraying different concentrations of GA₃10 d after flower bud formation was shortened by 7.64～19.3 d,but the differences in initial flowering period,full flowering period,late flowering period,flowering period and flowering rate were not significant（P>0.05）.Spraying different concentrations of GA₃on 60 d after flower bud formation shortened the flowering time by 75.34～110.28 d,advanced the initial florescence by 10.67～35.00 d,advanced the full florescence by5.33～47.33 d,and advanced the terminal florescence by 3.00～34.66 d;the florescence and flowering rate had no significant difference compared with the control（P>0.05）,suggesting that 60 d after flower bud formation could be used as the time point for GA₃treatment to blossom early.（2）Spraying GA₃with different concentrations(500～2500 mg·L^-1)60 d after flower bud formation,when the concentration of GA₃was 500-2000mg·L^-1,with the increase of the concentration of GA₃,days required for flowering,the initial flowering period,the full flowering period,the last flowering period and the day ahead of schedule gradually shorten,but when the concentration of GA₃exceeds 2000 mg·L^-1.Compared with the control（clean water）,the treatment of 2000 mg·L^-1GA₃significantly advanced the flowering day by 110.34 d（P<0.05）,the initial flowering period by 35 d（P<0.05）,the full flowering period by 47.33 d（P<0.05）and the final flowering period by 34.66 d（P<0.05）.（3）Principal component analysis was carried out based on the flowering indexes of different concentrations of GA₃in different periods.The treatment with the highest comprehensive score was spraying 2000 mg·L^-1GA₃60 d after flower bud formation.4.The physiological indexes such as soluble sugar,starch,soluble protein and photosynthetic pigment in leaves of Rhododendron treated with GA₃at early flowering stage were determined.The results showed that compared with the control,the contents of soluble sugar,starch,soluble protein,chlorophyll a,chlorophyll b and total chlorophyll in the leaves of rhododendron were significantly increased after GA₃treatment（P<0.05）.It indicated that GA₃treatment enhanced the ability of leaf to capture light energy,promoted the accumulation of soluble sugar,starch and protein in leaves,and made Rhododendron blossom earlier.In summary,the measures for regulating the flowering period of Rhododendron spraying growth regulators applied to park green space are as follows:（1）Promoting flower bud formation stage:30 d after flowering,2000mg·L^-1CCC was sprayed every 7 d for 3 times;（2）Early flowering stage:After 60 d of flower bud formation,2 000 mg·L^-1GA₃was sprayed every 7 d for 3 times.