| Peach is a kind of fruit tree,which is widely cultivated all over the world,but peach replant problem is a much challenged problem for the farmers.The toxic HCN released from the peach root residues left to the soil was frequently reported as one of the major agent that caused the peach replant problem,but generally,autotoxicity is not probably induced by single toxic substance.To investigate other potential toxic substances that would be able to caused replant problem could lead us to a more comprehensive understanding about the peach replant problem.Root exudates have been a hotspot in studying replant problem for years.In the current study,aiming to elaborate the effect of potential autotoxic substances on peach seedlings and their modes of action,we did a research on the isolation and quantification of the autotoxic chemicals in peach root exudates,root extracts,as well as in peach replant soil.The main results are as follow:1.The peach replant soil from peach orchard in Huazhong Agriculture University caused reductions in peach seedlings growth,and this phenomenon lasted for at least 4years.CN-contents in different sized peach roots were different,fine roots(? < 5 mm)contained more CN-than medium size roots(5 mm ? ? ? 10 mm)and large sized roots(? > 10 mm).CN-contents in bulk soil of both peach dead trees and growing trees increased year by year and former were higher than latter.In addition,total microbe population and activities of soil enzymes such as invertase,acid phosphatase and catalase in rhizosphere soil of peach dead trees decreased year by year,urease in bulk soil of peach dead trees showed the opposite trend.2.The aqueous extracts of peach replant soil were then extracted again with ethyl acetate water-saturated butanol and XAD-16 resin,the XAD-16 resin were washed with different concentration of methanol,the results of bioassay showed that the 100%methanol elute showed the strongest inhibitory.3.Sandy media planted with peach seedlings were wash with distilled water to collect root exudates peach seedlings,then XAD-16 resin was used to absorb the autotoxic chemicals in root exudates,meanwhile,bioassay results showed root exudates and extracts of peach root bark and wood contained toxic substances.4.Chemicals in replant soil,peach root exudates,ethanol extracts of root bark androot wood were analyzed with GC-MS.The results showed that major chemicals in replant soil were 3-hydroxy-dodecanoic acid,14-methyl-Hexadecanoic acid,methyl ester,stearic acid and palmitic acid.Major chemicals in peach root exudates were 1,2-Benzenedicarboxylic acid,diisooctyl ester,Bis(2-ethylhexyl)phthalate,palmitic acid and benzoic acid.Ethanol extracts of peach root bark and root wood mainly contained butylated hydroxytoluene,benzoic acid,palmitic acid,stearic acid and stearic acid,palmitic acid,2,4-bis(1,1-dimethylethyl)phenol,3,5-bis(1,1-dimethylethyl)-4-hydroxyBenzenepropanoic acid,octadecyl ester,repectively.5.Benzoic acid,palmitic acid,benzaldehyde,ethanol and water extracts of peach root bark were applied to peach seedlings,and they inhibited peach seedling growth in various degrees.The same concentration of benzoic acid and benzaldehyde caused a greater reductions in seedling growth than palmitic acid,and the inhibition of mixture of benzoic acid,benzaldehyde and palmitic acid were greater than the individual agent.The SOD,POD,CAT activity in roots of peach seedlings treated with ethanol extracts of root bark,benzoic acid,benzaldehyde and the mixture increased and then decreased.MDA contents in roots of peach seedlings were higher than that in control in all treatments.Except for palmitic acid,generally,other treatments inhibited photosynthesis and pigments of peach seedlings.Besides,TEM observation showed that all the treatments,in varying degrees,caused ultrastructure changes of root tip cells. |
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