| Long-term excessive use of chemical fertilizers,pesticides and continuous cropping has caused soil degradation and compaction,decreased soil fertility and reduced productivity,soil microbial flora has changed,pathogenic microorganisms have increased,and soil-borne diseases have become severe,leading to a vicious cycle and ultimately crops.The decline in quality,the increase in pesticide residues,and the serious damage caused by pesticides and fertilizers have seriously hindered the sustainable development of agriculture and threatened national food security.At present,the control measures for soil-borne diseases include physical control,chemical control and biological control.Physical control includes measures such as soil replacement and exposure to disinfection.Due to the large amount of engineering,the actual application effect is not ideal;chemical control methods will lead to increased resistance of pathogenic bacteria,causing pollution to soil and water;biological control mainly uses biocontrol microorganisms for control,But now the spectrum of single biocontrol bacteria is narrow,and the prevention effect is unstable.The use of a variety of bio-control microorganisms can implant a large number of beneficial microorganisms in the soil,which can compete and inhibit pathogenic bacteria,reduce pathogenic pressure,induce plant resistance,and promote plant growth,thereby achieving the effect of preventing soil-borne diseases.Rhizopus nigricans and Trichoderma pseudokoningii are two filamentous fungi with biological control activity isolated from the rhizosphere soil of plants in areas with severe soil-borne diseases.Based on the mixed fermentation broth of Rhizopus niger and Trichoderma koningii,this paper studied the mixed fermentation process.Through the analysis of the chemical composition of mixed fermentation,it was found that the process added antibacterial substances,increased substances that increased system resistance,and increased The material that promotes plant growth has a significant effect on the prevention and control of soil-borne diseases,improves the physical and chemical properties of soil and microbial flora,and uses the preparation to treat crops before harvest,and also improves the quality of fruits during storage after harvest.1.The inhibitory effect of mixed fermentation broth on plant soil-borne diseasesThe tests showed that the mixed fermentation broth can inhibit various plant-borne diseases.The inhibition rate of the mixed fermentation broth on F.oxysporum reached 61.12%.The results of the spore germination test and the fermentation broth test of the mixed fermentation broth achieved 92.83%.The mixed fermentation process has been established.The optimal combination is soybean meal 70 g/L,potassium dihydrogen phosphate 0.4 g/L,and soluble starch 30 g/L.The inoculation ratio of Rhizopus nigricans and Trichoderma pseudokoningii was 1:1,1:4,1:9,inoculation volume 2%;mixed fermentation temperature was 28?;fermentation time was 12 days;initial pH was 6.5.The fermentation broth of R.nigricans and T.pseudokoningii with a mixing ratio of 1:4 had the best inhibitory effect on A.alternata,reaching a rate of 66.73%,and that of B.cinerea reached 84.87%.In the field experiment,the relative control effect of the mixed microbial preparation on cucumber wilt and tomato gray mold reached more than 85%.The plant height,leaf number and stem thickness in each period were higher than those in the control group.It proved that the treatment of mixed fermentation broth had the effect of resisting disease and promoting growth.SOD,POD,PAL and other resistance-related enzyme activities have been improved to varying degrees.The mixed fermentation had more products than the single fermentation,in which the content of antibacterial substances such as phenols,aromatic compounds and methyl salicylate increased significantly,and the content of oligosaccharides which can induce plant resistance increased.These experimental results preliminarily showed the antibacterial mechanism of the mixed fermentation broth.2.Effects of mixed fermentation broth on soil physical properties,chemical properties and soil microfloraAfter treatment with mixed fermentation broth,the basic physical and chemical properties of the soil changed significantly.The results of the two-year experiment proved that the soil porosity,field water holding capacity,organic matter content,total nitrogen,available phosphorus and available potassium increased significantly,while the soil bulk density,pH,ammonium and nitrate nitrogen decreased.The contents of soil organic matter,total nitrogen,available phosphorus and available potassium were positively correlated with the application amount of mixed fermentation broth.The soil structure had become better,the content of organic matter increased,the degree of soil maturation increased,and the content of nutrients increased.After the application of mixed fermentation broth,the activities of soil urease,invertase and catalase had been greatly improved,which promotes the propagation of soil microorganisms and enhances the activities of related enzymes.The application of mixed fermentation broth had a obvious effect on the diversityof soil fungi.On the level of the class,the dominant populations were Dictyostelidae,Tremella and Trichophyceae,after treatment,the relative content of Dictyostelida decreased,while the relative content of Tremella and Trichophyceae increased.On the genus level,the relative content of Gibberella genus and Fusarium genus with morecommon pathogens in the treated soil were decreased significantly.On the species level,the relative contents of several pathogens such as Gibberella,Fusarium rotatum and Fusarium oxysporum had been significantly reduced.At the same time,it had a relatively obvious impact on the diversity of soil bacteria.After treatment,the relative content of Acidobacteria decreased on the class level,and the relative content of Proteobacteria,Actinomycetes and Clostridia increased.On the family level,the relative content of Xanthomonasceae and Alcaligenes increased significantly.On the species level,the relative content of several beneficial bacteria such as rhizobia,bradyrhizobium and nitrifying bacteria had increased significantly.It proved that the mixed fermentation broth has an inhibitory effect on the growth and reproduction of plant pathogenic fungi in the soil,and adjusted the soil microbial community to make it more conducive to plant growth.3.Effect of pre-harvest treatment of mixed fermentation broth on postharvest quality and preservation of kiwifruitAfter the mixed fermentation broth treatment,the relative control effect of kiwi ulcer disease reached 68.11%;the leaf photosynthesis efficiency increased by 11.58%,and the activities of defense-related enzymes SOD,POD,and PAL were significantly increased to varying degrees.In the postharvest kiwifruit experiment,compared with the control group,the single fruit weight increased by 27.69%,the fruit hardness increased by 2.15 times,the SSC increased by 34.40%,the titratable acid content increased,the ethylene production and respiration rate decreased,and related defenses enzyme activity increased.Postharvest experiments showed that the water loss rate of the fruit in the treatment group decreased significantly,the incidence of postharvest diseases decreased significantly,and the disease prevention effect reached 72.2%.The results of kiwifruit transcriptome experiments showed that in terms of postharvest fruit disease resistance,the transcription level of related enzymes in the flavonoid synthesis pathway related to antioxidant resistance,auxin transport was most significantly up-regulated,auxin,cytokinin,The transcription levels of genes related to plant hormone signal transduction such as gibberellin and salicylic acid also increased significantly,and the expression levels of various disease-resistant protein genes were up-regulated,which effectively improved the disease resistance of fruits.In terms of inhibiting ripening of fruits,the expression of auxin-related genes(AUX/IAA)was up-regulated and significantly after mixed fermentation broth treatment;it significantly promoted the alanine ammonia-lyase(PAL)catalase(CAT)and glutathione in fruits Glyphosate peroxidase(GPX)gene expression.At the same time,it inhibited polygalacturonase(PG),pectin esterase,?-glucosidase,?-1,3-glucanase,and polygalacturonase in kiwifruit in the late storage period.The expression levels of fruit-related transcription factors RIN4 and CNR6 were significantly reduced;the expression levels of the two most important rate-limiting enzymes,ACS3 and ACO,were significantly down-regulated in the pathways related to ethylene synthesis,and the negative regulators CTR1,EIN3 and The expression level of EIN4 was significantly up-regulated.The experimental results prove that the pre-harvest treatment of the mixed fermentation broth can delay the ripening of kiwifruit by inhibiting the cell wall degradation process and related gene expression in the ethylene synthesis transduction pathway.The results of metabolomics experiments showed that after harvest,the content of plant hormones changed,the content of auxin and salicylic acid increased,the content of abscisic acid decreased,and the content of various amino acids,vitamins and flavonoids increased.These results prove at the genetic level that the mixed fermentation broth promotes fruit development,improves fruit quality,and prolongs the shelf life of the fruit.In summary,the mixed fermentation broth of R.nigricans and T.pseudokoningii can improve the physical and chemical properties of soil,improve the soil microbial flora,effectively inhibit the growth of plant pathogenic microorganisms,and thus achieve the purpose of preventing soil-borne diseases.Postharvest experiments on kiwifruit showed that preharvest treatment of mixed fermentation broth effectively improved postharvest fruit quality and prolonged fruit storage time.This study provided a new idea for biological control of plant diseases and stress-resistant production,which is of great significance to the national pesticide and chemical fertilizer efficiency and application strategies and the development of sustainable agriculture. |
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