| Plant-parasitic nematodes severely infected banana in acidic,sandy soil in Hainan,China.In the past,nematode control mainly relied on the use of chemical nematicides which were quick,but of poor performance.Increasing public interest in protecting the environment and human health has prompted research focusing on the reduction of the use of fungicides and herbicides.Alternative control methods with high efficacy,low cost,and limited environmental effects are a high-priority research area for contemporary agriculture.In this study,ammonium bicarbonate and lime were used as the soil fumigant.We screened the application model of fumigant,and investigated its control effect on plant-parasitic nematode and effects on nematode community.We also screened the endophytes against nematodes and investigated its control effect on plant-parasitic nematode and biocontrol mechanism.We investigated the effects of soil fumigation combined with banana seedlings colonized functional endophyte on plant-parasitic nematode and nematode community in pot and field conditions in order to provide theoretical and technical support for root-knot nematode control.The main results were summarized as follows:1.Screening results of soil fumigants showed that a mixture of lime and ammonium bicarbonate(LAB)in suitable additive amounts(0.856 g/kg soil of L and 0.428 g/kg soil of AB)showed stronger nematocidal ability than the use of ammonium bicarbonate alone and control(with no additives)with the proportion were 50%and 66.2%,respectively.LAB showed an significant nematocidal effect at low soil moisture and large temperature range.Fumigation could improve soil properties,including soil pH,NH4+-N NO3-N and total nitrogen contents.Results of pot experiments showed that LAB had an excellent nematocidal ability on plant-parasites and total nematodes,especially for Meloidogyne and Rotylenchulus after fumigation.The number of plant-parasitic nematode in root in LAB treatment were significantly lower than control(with no additives)with the reduction of 88.6%after harvest.Field experiment results showed that LAB is a potentially effective strategy to suppress soil nematode damage in acidic,sandy soils,especially those affected by plant-parasitic nematodes in fields with serious nematode infected,especially for Rotylenchulus.Fumigation could improve soil properties,including soil pH,NH4+-N,NO3--N and total nitrogen contents,while pH and NH4+-N contents were negatively related to plant-parasites.Application of LAB changed the composition of soil nematode community which decreased maturity index(MI),increased PPI/MI ratio,shannon index(H')and evenness(J)in the first field experiment,while no significant difference was observed in ecology indexes in the second field experiment,indicating the soil ecosystem after LAB fumigation was recovering.2.Result of antagonisitic root-knot nematode test showed the proportion of antagonistic bacteria were significantly higher than fungi in three disease levels of roots,indicating that bacteria possessed greater potential for the biological control of nematodes.The relative abundances of antagonistic endophytes were higher in the roots of middle and high disease levels with the proportion of over 60%.Among those,bacteria were dominant,and Pseudomonas,Bacillus and Streptomyces showed more abundant populations with the relative abundance of 30.6%,22.2%and 19.4%,respectively.Most of the antagonisitic bacteria could be successfully colonized in banana roots.One strain,named as SA,with definite root inner-colonization ability was identified as Streptomyces sp.SA could promote banana growth,and had significant control effect on plant parasitic nematodes in roots and soils,especially for Meloidogyne.RT-PCR results showed that the abundance of total bacteria in root was decreased after the regulation of SA,while no significant difference of actinomycetes was observed.The abundance of total bacteria and actinomycetes in soil affected by SA(SA1)were significantly decreased compared with sterile banana seedlings(CK1).Rhizosphere microbial community collected from SA1 was inoculated to sterile banana seedlings and formed new rhizosphere soil(SA2).The banana seedlings and soil of SA2 were transplanted into deseased soil and form new rhizosphere soil(SA3).The abundance of total bacteria and actinomycetes in soil of SA3 were significantly decreased compared with that of sterile banana seedlings(CK3).MiSeq sequencing was used to detect the bacteria community in root and rhizosphere regulated by SA.Principal coordinates analysis showed that the samples of the three stages were effectively distinguished.The cluster tree showed that the bacteria structureof SA in root and soil were different from that of sterile banana seedlings(CK).The composition of phylain root and in soil with the relative abundance over 0.1%has changed significantly.The relative abundance of Proteobacteria and Actinobacteria in SA was higher than that of sterile banana seedlings(CK).The relative abundance of Bacteroidetes and Proteobacteria in SA1 was higher than that of sterile banana seedlings(CK1)in stage 1.The relative abundance of Actinobacteria in S A2 was higher than that of sterile banana seedlings(CK2)in stage 2.The relative abundance of Acidobacteria,Actinobacteria and Firmicutes in SA3 was higher than that of sterile banana seedlings(CK3)in stage 3.There was a significant correlation between the bacterial community and the abundance of plant-parasitic nematodes rhizosphere soil in stage 1 and in root.The relative abundance of Erwinia,Kluyvera,Yokenella,Castellaniella and Pseudomonas increased in SA was significantly negatively correlated with the abundance of plant parasites.The antagonistic bacteria in root of SA showed that the proportion of Enterobacter,Streptomyces,Serraria and Pantoea were higher than that of sterile banana seedlings(CK).These isolates which belonged to Proteobacteria and Actinobacteria were significantly higer than that of sterile banana seedlings(CK),respectively.The proportion of Streptomyces and Bacillus with antagonistic ability in soil of SA3 was also significantly higher than that of sterile banana seedlings(CK3).They belonged to Actinobacteria and Firmicutes which were significantly higer than that of sterile banana seedlings(CK3),respectively.3.Pot experiment results of soil fumigation combined with biocontrol agent(LSA)showed that the combination control could promote banana growth and had significant control effect on plant parasitic nematodes in root and soil,especially for Meloidogyne.Application of LSA might reduce the disturbance of soil caused by single fumigation.Results of field experiment showed that the application of LSA had significant suppression on plant-parasitic nematodes in root and Tylenchus in soil,as well as increased banana yield.Little effects on soil disturbance and nematode community were caused by utilization of LSA.The greatest impact of soil physicochemical properties was to improve soil pH.Conclusion:Lime and ammonium fumigation combined with biocontrol agents,can promote banana growth and have significant control effect on plant parasitic nematodes in root and soil,both in greenhouse and field conditions.Microbes in root and soil,nematode community structure and soil physicochemical properties of soil develop to a trend of disease suppressive soil after the application of LSA. |
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