Study On The Effect Of Plant Growth Retardants On Drought Resistance Of Dahlia

Dahlia pinnata Cav.is a perennial herbaceous flower of the genus dahlia.It has a beautiful flower color,diverse flower shapes,long flowering period,and high ornamental value.It is widely introduced and cultivated.Dahlia is native to the highlands of Mexico and suitable for sunny and cool environments.It is very sensitive to moisture,and it is neither tolerant to waterlogging nor drought.In actual production,drought is the main environmental factor affecting the growth and flowering of dahlia.Paclobutrazol(PP333)and uniconazole(S3307)are important plant growth retarders,which have a good effect in regulating the plant shape of dahlia,but there are few reports on its drought resistance in dahlia.This study investigated the effects of PP333 and S3307 on the growth,photosynthetic characteristics,physiological and biochemical indexes of dahlia under drought stress by using dahlia ’Dan Banhuang’ potted seedlings as experimental materials.The membership function analysis method and principal component analysis method were used to comprehensively evaluate the drought resistance effects of different treatment groups,and the key drought resistance identification indicators were screened out.The main test results obtained are as follows.1.The effects of PP333 and S3307 on the physiological and biochemical indexes of dahlia under drought stress were investigated by using 100-200 mg·L-1 PP333 and 10-50 mg·L-1 S3307.The results showed that under drought stress conditions of 5 days,10 days,15 days,the contents of MDA and proline continued to increase.The content of soluble sugar and the activities of SOD and CAT increased first and then decreased.The activity of POD continued to increase.After rehydration for 5 days,various physiological indicators declined,but failed to return to normal levels.PP333 and S3307 pretreatment reduced the contents of MDA,proline.But increased the content of soluble sugar and the activities of SOD,POD,CAT.After rehydration,it is beneficial to the physiological repair of dahlia.However,the effects of different concentrations of PP333 and S3307 on the regulation of drought resistance in dahlia are significantly different.Among them,125-150 mg·L-1 PP333 and 20-30 mg·L-1 S3307 trement effect is better.2.The effects of exogenous PP333 and S3307 on photosynthesis of dahlia under drought stress were investigated by measuring changes in photosynthetic indexes of dahlia under different treatment conditions.The results showed that drought stress significantly reduced the relative content of chlorophyll and Pn,Gs,Tr in dahlia.Ci decreases in the early stage of stress,but rises in the late stage of stress.After rehydration,the relative content of chlorophyll and Pn,Gs,Tr,Ci all increased.Exogenous PP333 and S3307 treatment alleviated the decrease of relative chlorophyll content,Pn,Gs,Tr under drought stress,and inhibited the increase of Ci in the later stage of stress.In addition,they promote the restoration of photosynthesis after rehydration.3.The effects of exogenous PP333 and S3307 on the growth status and mineral element content of dahlia after 15 days of drought stress were studied.The results showed that drought stress significantly reduced the plant height growth,root biomass,aboveground biomass,and the contents of N,P,K,but significantly increased the root-shoot ratio.Both PP333 and S3307 significantly reduced the growth of plant height,and the higher the concentration,the better the inhibitory effect.PP333 and S3307 also increased the root biomass,root-shoot ratio,and the contents of N,P,K to varying degrees.The effects of 150 mg·L-1 PP333 and 30 mg·L-1 S3307 were significant.The results indicated that PP333 and S3307 treatment could promote the distribution of photosynthetic products to the root system,enhanced the growth of roots,facilitate the absorption of water and nutrients to alleviate the damage of drought stress.4.Applying membership function analysis method and principal component analysis method to comprehensively evaluate the drought resistance effect of dahlia under different treatment conditions.The results showed that compared with the drought stressed control group,exogenous PP333 and S3307 treatments improved the resistance of dahlia to drought.Among them,30 mg·L-1 S3307 treatment had the best effect,and 150 mg·L-1 PP333 treatment effect is second.At the same time,root dry weight,root shoot ratio,leaf total phosphorus content,Tr,Pn,MDA content,CAT activity and soluble sugar content were screened as important indicators of drought resistance identification of dahlia.