Study On The Relationship Between Dominant AM Fungi And Root Rot Pathogens In Continuous Cropping Soybean Soil

Three representative soybean varieties,Ken Feng 16(KF16),Hei Nong 44(HN44)and Hei Nong 48(HN48),with a larger promoting planting area in Heilongjiang province were selected in this study and planted in sterilized continuous cropping soybean(CCS)soil,inoculated with the screened AM fungi Funneliformis mosseae who predominated in CCS soil,and with Fusarium oxysporum,a pathogenic bacteria that lead to soybean root rot,taking un-inoculated F.mosseae as blank control(CK).Real-time fluorescent quantitative PCR(qRT-PCR)was employed to detect the DNA levels ofF.mosseae and F.oxysporum in soybean root system and in rhizosphere soil so as to make clear the relationship between AM fungi(FR mosseae)and pathogenic bacteria(F.oxysporum),aim at revealing the influence of AM fungi on pathogenic bacteria of soybean root rot and further elucidating the inhibition mechanism of AM fungi to soybean root rot,which will provide theory evidence for solving the problems generated in soybean continuous cropping.1.Microbial inoculum was prepared by three-level activation of F.oxysporum on sorghum medium,and the final bacteria concentration was 1.0×107cfu/ml.They could effectively infect soybean root system and rhizosphere soil.2.The infection status of F.mosseae and F.oxysporum on the root system of different soybean varieties at every development stage was detected.The whole genome from root system and rhizosphere soil of different varieties and different treatments was extracted,and PCR amplification to detect the infection levels of F.mosseae and F.oxysporum on soybean plant roots from every development stages was carried out.The results showed that the root system and rhizosphere soil from different varieties or.from the same variety of different stages all observed witlh infection by F.mosseae and F.oxysporum.3.The changes in DNA contents of F.oxysporum from the same soybean variety among different treatments were measured by qRT-PCR,and the results of which showed the average F.oxysporum DNA levels in both root system and in rhizosphere soil from KF16,HN44,HN48 inoculated with F.mosseae were all lower significantly than those prior to F.mosseae inoculation,indicating the strong antagonism of F.mosseae on F.oxysporum.4.Meanwhile,qRT-PCR was used to determine the changes in DNA contents of F.oxysporum from the same soybean variety among different stages.The results showed that whatever in root system or in rhizosphere soil,the F.oxysporum DNA levels in KF16,HN44 and HN48 from branching stage were significantly higher than from seedling stage5.The changes of F.oxysporum DNA contents among different treatments from different soybean varieties were measured using qRT-PCR.The results showed that at both seedling stage and branching stage,and whatever in root system or rhizosphere soil,the averageF.oxysporum DNA levels from treatment groups of different soybean varieties were significant lower than from CK group.At whatever seedling stage or branching stage and in whatever root system or rhizosphere soil,the average F.oxysporumDNA levels of the three varieties from different treatment were not total the same,suggesting significant difference of infection degree existed among the three soybean varieties.The infection degree displayed the most obvious in KF16,followe'd by HN44.6.The changes in DNA levels of F.oxysporum at different stage of.the same soybean variety were analyzed using qRT-PCR.The results showed that in whatever root system or rhizosphere soil,the F.oxysporum DNA levels o in branching stage were dramatically.higher than those in seedling stage.7.The relationship between F.mosseae and F.oxysporumF.mosseae had a strong inhibition effect on F.oxysporum derived from theinfection status of soybean roots of different varieties by F.mosseae and F.oxysporum and the qRT-PCR results.In detail,the changes in F.oxysporum DNA levels among different treatments of the same variety,and the changes of F.oxysporum DNA levels in between treatments among different varieties as well as in the same variety from different development stages,confirmed that significantly differences existed in F.oxysporum DNA levels between inoculated with F.mosseae or without,and the change results indicated the antagonism of F.mosseae against F.oxysporum.