Effect Of Intercropping Cassave On Rubber Tree White Root Disease And Soil Microecological Environment

Intercropping cassava in young rubber is one of the common planting patterns in rubber planting areas at home and abroad.However,there has been a controversy on the rationality of this intercropping pattern.Therefore,the effects of cassava allelochemicals on the growth of pathogenic bacteria were researched by dual culture on the PDA plate,incluing the water and alcohol extracts from cassava organs,the water and alcohol extracts from cassava organs decomposed,leaf volatiles,root exudates of cassava and the water extracts from rubber soil.The effects of cassava root water extract on the growth and disease index of rubber seedlings infected with white root disease were studied by potted experiment.The differences of soil fertility and soil microbial structure after intercropping cassava under the conditions of fertilization and no fertilization was studied in three different years by field experiments.Therefore.the research can answer the divergence point whether the declining of soil fertility and increasing the occurrence of disease can be caused after intercropping cassava,thus can provide certain theoretical supports for the rationality of the rubber/cassava interplanting pattern,and guidance for promoting and optimizing the interplanting cultivation.The main results are as follows:(1)In cassava organ extracts,all the concentrations of root water had significant allelopathic promotion effects on the growth of pathogen.The alcohol extracts had significant allelopathic promotion effects at concentrations of 8,40 and 200 mg/ml.The allelopathic effects of stem water and alcohol extract on the growth of pathogen has no obvious rule;the allelopathic promotion effect of leaf water on pathogen growth is mainly concentrated at 10,100mg/ml,and the alcohol extracts had significant inhibition effects mainly concentrated in the first two days after the treatment of 200 and 1000 mg/ml.The inhibition effect of root rot water extracts reached significant at 200mg/ml;the stem decomposing water extracts at all concentrations had significant allelopathic inhibition effect on pathogen growth.The allelopathic inhibition effect of alcohol extract on pathogen growth was concentrated at 8 mg/ml,and the allelopathic promotion effect on pathogen growth was concentrated at 200 and 1000 mg/ml;the leaf decomposing water extracts had significant allelopathic inhibition effect on pathogen growth at 8 and 40 mg/ml,and the alcohol extracts had a significant promotion effect at 8,40 mg/ml.The volatiles of cassava leaves had significant allelopathic inhibition effect on pathogen growth at 4 and 6 g/dish.Root exudates have no significant allelopathic effect on pathogen growth.The allelopathic promotion effect of soil water extracts on pathogen growth was concentrated at 40,200,1000mg/ml for 2d.(2)The cassava root water extract showed significant allelopathic promoting effects on white root disease in rubber trees,so 10mg/ml cassava root water extract was selected and irrigated to rubber seedlings inoculated with white root disease.Five months later,it was found that the root infection degree is more serious than control group,"1" grade infection rate showed 20%less than that in control group,"3" grade infection rate showed 20%higher than that in control group,and that irrigation of the cassava root water extract could delay leaf yellowing and leaf falling compared with control.This indicated that cassava root water extract could indeed aggravate the degree of white root disease of rubber seedlings in the long run,but in the short run,root water extract could improve the growth of rubber seedlings.(3)Based on the principal component analysis of the change rate of soil fertility and soil microbial structure index in the first and third year intercropped without fertilization,in the second year intercropped with fertilization,it was found that the comprehensive score values of soil fertility and the soil microbial structure in the first and third year intercropped without fertilization were less than zero,and the comprehensive score values of soil fertility and the soil microbial structure in the second year intercropped with fertilization were greater than zero.This indicated that intercropping cassava without increasing fertilization could cause soil fertility decline and soil microbial structure deterioration,while applied fertilization to intercropping plantation could increase the soil fertility and improving soil microbial structure,which was beneficial to resist plant defend against diseases,also could ensure high and stable yield of rubber.High-throughput sequencing technology was used to analyze the changes in soil fungi and bacterial community structure diversity.The main bacteria include:Prote obacteria,Acidobacteria,Actinobacteria,Firmicutes,Verrucomicrobia,ChLorofLexi a nd PLanctomycetes.The main fungi include:Ascomycota,Basidiomycota,Zygomycot a,Chytridiomycota,GLomeromycota.Intercropping alters the structure and compositi on of bacterial and fungal communities,which may result in decreased soil micro-e cological environment resistance to disease and reduced soil degradation and metabo lic activity.