Factors Influencing On The Budding Of The Tuberous Root Of Rehmannia Glutinosa Libosch

Rehmannia glutinosa Libosch is one of the medicinal plants cultivated for a long history.The widely adopted cultivation mode is propagating vegetatively with its developing tuberous roots in the last summer,and then plant in the early spring with the cuttings of newly formed tuberous roots as propagating materials.It has been found that the seedling emergence was poor and most of the propagating materials rotted in the field.It might be related to the factors such as high temperature,drought and/or harmful microorganisms.In this paper,the effects of temperature,water loss,antimicrobial and plant growth accelerating agents were systematically investigated on the budding of the tuberous root cuttings of R.glutinosa and the mechanisms of water loss affecting the budding were preliminarily revealed.The main results are as follows:1.Effects of different factors on the budding of tuberous root cuttings(1)TemperatureTo mimic the traditional propagating technique,the newly cuttings were treated with the powder of quick lime and placed on the bed of wet vermiculite,and cultured at different temperatures.It was found that the budding rate and the average number of budding per cutting increased with the increase of temperature,within the scope of 25℃ to 35℃,but the rotten rate was the opposite,all the cuttings rotted at 38℃ and 40℃.(2)Water lossIn this study,the cuttings were placed in a thermostat at 25℃ and allowed to lose water to simulate wilting caused by drought.When the water loss reached to 0%,10%,15%,20%,25%or 30%,the root cuttings was placed on wet vermiculite,and cultured under black film at 14℃-18℃.It was found that rotten rate was proportional to water loss,and nearly all the cuttings rotted away when water lost up to 25%and 30%.The budding rate and average bud number per cutting were negatively correlated with water loss.In addition,the ends of cuttings were found blackened.(3)Bacteriostatic agentsIn this study,several bacteriostatic agents including carbendazim,kasugamycin,ethylicin,pyraclostrobin+ethylicin,chloroisobromine cyanuric acid and streptomycin were used to treat the cuttings and those treated with quick lime as control.Culturing method followed as the previous ones in section(2).The results showed that bacteriostatic agents could improve the budding of root cuttings when compared with the control treatment,and the best effect was achieved when the root cuttings were treated with chloroisobromine cyanuric acid and cultured at 35℃.(4)Plant growth acceleratorsIn this study,plant growth accelerators including gibberellin,brassinosteroid and 6-benzylaminopurine were used to treat the root cuttings with quick lime treatment as control.The culturing method was the same as described in section(2).The effects of all the treatments were better than that of control,and the best one was gibberellin treatment.2.Mechanism of water loss affecting on the budding of root cuttings(1)Changes of some components in the root cuttings during water lossIn this study,the root cuttings of R.glutinosa were incubated in an incubator at 25℃ and water was allowed to lose up to 0%,5%,10%,15%,20%,25%and 30%,and at the same time,each treatment was set a moisture holding control.The contents of sugars,catalpol,abscisic acid and malondialdehyde(MDA)were determined.It was found that,in the moisture holding groups,the contents of manninotriose and fructose increased with the incubation time,while those of stachynose,sucrose,raffinose and catalpol were the opposite,MDA increased in the early stage and then decreased.In the water loss treatment groups,the changes of sugars and catalpol were found more intense and MDA increased earlier than those of the corresponding controls.In addition,abscisic acid was not detected in all samples.(2)Effects of blackened root cuttings on virus-free plantlets of R.glutinosaIn this study,the extract of blackened root cuttings was prepared and added into MS medium in different doses to in vitro culture the virus-free plantlets of R.glutinosa with different additions of fresh root extract as controls.The results showed that fresh root extract had no significant effect on the growth and development of the plantlets,while the blackened root extract dramatically inhibit the growth of the plantlets.(3)Effects of blackened root cuttings on the budding of R.glutinosa root cuttings and the germination of maize and wheat seedsIn this study,the root cuttings of R.glutinosa and the seeds of maize and wheat were soaked in the extract of blackened root cuttings at the concentrations of 0.00,0.05,0.10 and 0.20g/ml respectively,and then cultured in a chamber set at 25℃.It was found that the treatments could reduce the rotten rate of root cuttings,but dose-dependently inhibit the germination of wheat and maize seeds.In conclusion,the results of this paper indicate that:①water loss,high temperature and harmful microorganisms are all related with poor budding rate and high rotten rate of the root cuttings of R.glutinosa;②the black products formed during water loss may be responsible for the poor budding rate,which has no obvious ralationship with abscisic acid.Therefore,before planted,the root cuttings of R.glutinosa are suggested to be pretreated with bacteriostatic and plant growth accelerating agents,and after planted,soil moisture management should be strengthened.If mulching with plastic film was applied,soil temperature should be closely monitored to avoid high temperature damage.