Research On Mechanism Of Continuous Cropping Obstacle And Resistance To Root Development Of Rehmannia Glutinosa Libosch

Rehmannia glutinosa Libosch,a member of Scrophulariaceae family,its roots has been widely used as a herbal medicine with a long history in China.However,R.glutinosa has a serious replant problem.It requires 10 years to replant R.glutinosa in the same field after cultivation of this species,so replant problem is the mian factor limiting R.glutinosa development.The most intuitive manifestation of the continuous cropping obstacle is that the roots cannot expand normally,and the production and quality are declined.The requirements of the local Chinese medicinal materials for the growing environment and the restrictions of the “Huai District” area,so the mechanism of exploring the problem of continuous cropping of R.glutinosa is an urgent problem to be solved.It is generally believed that there may be three reasons for the continuous cropping obstacles.One is the change of soil physical and chemical properties and the imbalance of nutrients,the second is the infection of pests and diseases,and the third is the plant allelopathy.Previous studies on the obstacles of continuous cropping of R.glutinosa have focused on the allelopathic effects of plants and the imbalance of soil microbial flora.There is no systematic comparison of these three cases.This study systematically compared these three situations.Taking the first plant as control,the second plant as treatment.The first plant was cultivated in the soil which was not cultivated with R.glutinosa about 10 years.The second plant was cultivated in the soil which was cultivated with R.glutinosa in the last year.The treatment that fertilizing the soil in time to improved physical and chemical properties and to make sure the soil nutrients enough is called trace element.The three groups of fields are managed in a unified manner,and make sure there is no serious pests and diseases occur during the growth.During the growth of R.glutinosa,the aerial parts of R.glutinosa was measured,including leaf length,leaf width,crown width,number of leaves and plant height;the morphological indicators of the underground part,including root length,root diameter,fresh weight per plant and drying rate,were determined;paraffin sectioning and staining were observed in the growth period;growth hormone was measured on root;root and leaf were used.The extract was subjected to allelopathic determination of R.glutinosa seeds.The results showed that:(1)The damage caused by continuous cropping obstacles to the R.glutinosa began from the pull-up period.The plants showed that the upper part of the leaves became smaller,the crown width became smaller,and the number of leaves became less.The underground part showed that the root length became shorter,the root diameter became smaller,and the roots of the roots became fresher reduced.Compared with the second plant,there is no significant difference between the trace amount of the aboveground part and the underground part.It indicates that the continuous cropping obstacle of R.glutinosa is not caused by diseases and soil physical properties and lack of nutrients.Continuous cropping obstacles not only lead to differences in plant morphology,but also lead to a decline in the medicinal quality of R.glutinosa.(2)The water extract of R.glutinosa root and leaves inhibited the growth seeds,and the effect of leaves was greater,the content of toxicants was higher.Compared with the roots of the first plant,the roots of the second plant were more inhibited at the same concentration.It is indicated that the main cause of the continuous cropping of R.glutinosa a is allelopathic.The allelochemicals come from the plants themselves and are released into the soil after one year of growth,which is toxic to the next year's plants.The longer the continuous cropping period,the greater the allelopathic effect.(3)The roots of R.glutinosa caused by continuous cropping obstacles cannot be inflated.The direct cause is that the vascular layer formation activity of the roots is hindered,resulting in a decrease in the rate of xylem formation inward of the formation layer and an increase in the rate of outward formation of phloem,resulting in a smaller proportion of xylem.The indirect cause may be the synthesis and transport of auxin,gibberellin and cytokinin,and the interaction of multiple hormones forms a complex regulatory network.