Effects Of Prebiotics On Enhancing Biocontrol Of Bio-Organic Fertilizers Against Tomato Bacterial Wilt

The outbreak of soil-borne diseases seriously restricts development of agriculture and improvement of crop economic benefits.In terms of soil-borne diseases suppression,bioorganic fertilizers have been widely studied due to the high efficiency of biocontrol and environmentally friendly.Bio-organic fertilizer(BOF)can suppress soil-borne disease via promoting plant growth,inhibit pathogen activity and modulating rhizosphere microbiome.However,nutrient in soils cannot support growth of beneficial bacteria in the BOF under complex field conditions.Beneficial bacteria lose the ability of growth,colonization,and competing with indigenous microbiome,as specific nutrient is scarce.This would result in low biocontrol efficiency of BOF.Therefore,in order to improve biocontrol efficiency of BOF,it is important to seek a way of selectively enhancing growth and activity of beneficial bacteria.Prebiotics are substances that selectively enhance the activity of beneficial bacteria and regulate the microbial community.Application of prebiotics in the intestine can selectively promote the growth of beneficial bacteria and maintain the health of hosts.Similarly,biocontrol efficiency of beneficial bacteria can be improved by adding prebiotics in the rhizosphere.Previous study shows that cycloserine and inulin are prebiotics for beneficial bacteria QL-A6(Ralstonia pickettii)and HR92(Lysinibacillus sphaericus),respectively.In vitro study shows that these two prebiotics can significantly promote suppression of beneficial bacteria on Ralstonia solanacearum and promote the growth of beneficial bacteria,respectively.Cycloserine can significantly inhibit Ralstonia growth,while inulin has no significant effect.In the greenhouse experiment,cycloserine and inulin can also significantly improve biocontrol efficiency of beneficial bacteria.Whereas,it is unclear that whether prebiotics can increase biocontrol of BOF in the fields.Therefore,cycloserine and inulin were selected in this study.Four kinds of BOFs fermented from two beneficial bacteria(QLA6 and HR92)and two kinds of organic fertilizers(livestock manure and Chinese medicine residues)were applied in the greenhouse experiment before adding prebiotics.Disease incidence of bacterial wilt and plant growth were measured to investigate the effects of prebiotics on biocontrol efficiency of different BOFs,after which the best combination of prebiotic and BOF were determined.In addition,we also studied the effects of frequency of adding prebiotics in soils on disease suppression of BOF and regulation on soil microbiome.The main findings are as follows:1.Disease suppression of OF1 significantly increased with the application of two kinds of prebiotics,respectively.Compared with OF1,disease incidence,area under the disease curve(AUDC),and pathogen density decreased 43.43%,43.93%,and 11.68%,respectively,with the addition of cycloserine.After adding inulin,disease incidence,AUDC,and pathogen density decreased 50%,47.98%,12.41%.Prebiotics improved biocontrol efficiency of BOF,which fermented from livestock manure and beneficial bacteria.Specifically,compared with BOF1-A6,cycloserine reduced 40.48% disease incidence of bacterial wilt,74.54% AUDC,and 17.10% pathogen density.There was no significant difference between with and without inulin.2.Two kinds of prebiotics could significantly promote tomato growth.In detail,cycloserine and inulin promoted shoot height,dry weight of shoot,and chlorophyll relative content of tomato plants,compared with OF1.In terms of two BOFs,two prebiotics had the same effects on shoot height,dry weight of shoot,and chlorophyll relative content.3.Frequency of prebiotics addition had different impacts on disease suppression of BOFs.Compared with BOF1-A6,adding cycloserine once and three times could both reduce disease incidence,disease rate,AUDC,and pathogen density.Whereas,frequency of prebiotics addition had no significant differences.Compared with BOF1-HR92,adding cycloserine three times significantly decreased disease incidence,AUDC,and pathogen density,which all lower than adding cycloserine once.4.Addition of cycloserine and inulin could significantly promote colonization of beneficial bacteria and regulate rhizosphere microbiome.Compared with BOF1-A6,cycloserine enhanced abundance of QL-A6 in the rhizosphere,but there was no significant difference between once and three times addition.Meanwhile,adding cycloserine once could increase relative abundance of Chloroflexi.Relative abundance of Acidobacteria and Bacteroidetes increased,while Actinobacteria and Firmicutes decreased.Compared with BOF1-HR92,abundance of HR92 significantly accumulated in the rhizosphere after adding inulin three times.Together,α diversity of rhizosphere bacterial community reduced,and βdiversity changed.Especially,relative abundance of Bacteroidetes and Patescibacteria increased,while relative abundance of Chloroflexi and Gemmatimonadetes decreased.Therefore,two prebiotics had distinguished impacts on disease suppression of BOFs.The same as frequency of prebiotic addition.In general,cycloserine significantly promote biocontrol efficiency and growth promotion of BOF1-A6.But adding more cycloserine has no effect.On the aspect of inulin,adding more inulin(three times)improve disease suppression of BOF1-HR92.All these findings can provide basics and framework of enhancing biocontrol efficiency of BOF in the future.