| In order to study the inhibitory effect of root exudate on the growth of Rehmannia and the composition of allelochemicals and their action mode,both pot-experiment and bioassay of seeds germination were used in this paper.The root exudate was extracted by 70% methanol from rhizosphere soil of Rehmannia and the tested cultivar is Rehmannia variety "Wen 85-5".The role of root exudate in the growing Rehmannia was revealed by removing them from the pot with water.The principal formation time of autotoxic-chemical was investigated by adding root exudates(collected in different growth stage)to the soil before plant Rehmannia.Methanol extraction was consecutively partitioned with different solvents.The allelopathic potential of each section was analyzed by seeds generation and pot experiment,The HPLC was employed to detect the phenolic acids and their content in the different sections.Main conclusions are as follows:(1)Removing the root exudate regularly can promote the growth and development of Rehmannia.Physiological indexes in the treatment group at seedling stage and elongation stage were higher than control group.Root fresh weight of Rehmannia in the treatment group was higher than the control group.Fresh weight and dry weight of root of the control group was just 83.49% and 82.39% of them in the treatment group at harvest.There is no significant different in the growth of overground part between the control group and treatment group.While the membranes of the leaves in the control group were damaged.(2)The growth of Rehmannia was inhibited by adding root exudate collected in different periods into the pot.The root fresh weight of Rehmannia in treatment groups which added the root exudate was lighter than control group(the first cropping Rehmannia)at harvest,The smallest one is group E,its weight is 17.94 g,just 39.42% of the first cropping Rehmannia.The weight of Group A,group B,group C and group D was 66.68%,51.89%,47.16%,85.76% and 47.05% of that of the first cropping Rehmannia.(3)Allelopathy of aqueous section and n-butanol section of root exudate is stronger than other sections.There is a close relationship between content of phenolic acids in allelochemicals and allelopathic potential.Aqueous section had a strongest inhibitory effect on seed germination and root elongation growth while n-butanol section had the strongest inhibitory effect on Rehmannia fibrousroot.Seed germination of aqueous section was 51.11% in 4 times concentration groups,the root length was 5.29 mm,RI-0.43,while the seed germination of n-butanol section was 65.56%,root length was 7.22 mm,RI-0.22.The leaves of n-butanol section were damaged and the development was affected at seedling stage in pot experiment.At harvest time,Rehmannia root fresh weight of n-butanol section groups was 19.75 g,just 43.9% of that in the first cropping Rehmannia,the fresh weight of aqueous section groups was 26.25 g,58.3% of that in the first cropping Rehmannia.HPLC testing results showed that the combination of phenolic acids in different extract sections was different.Petroleum section and chloroform section had no phenolic acids,while n-butanol section and aqueous section had most species of the five phenolic acids.N-butanol section contains coumaric acid,vanillic acid and p-hydroxybenzoic acid,and content of total phenolic acids was the highest,2.094 μg/m L.Aqueous section had vanillic acid,p-hydroxy benzoic acid,clove acid and ferulic acid,and content of total phenolic acids was 1.107μg/m L.The section which contains the most phenolic acids was same with the section which has the strongest allelopathy.Phenolic acids may be the allelochemicals which caused the replanting disease of Rehmannia.(4)Adding phenolic acids into soil decreased survival of Rehmannia.Growth of Rehmannia in different phenolic acids treatment was different.The allelopathy of mixed phenolic acids was close to the replanting Rehmannia. |
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