| Root rot disease is one of the important factors that restrict the sustainable development of Astragalus in recent years.This is particularly true in Shanxi,the natural habitat of Geo-authentic Astragalus.This study focuses mainly on the Astragalus root rot occurring in Hunyuan,Wuzhai,and Yingxian,three main growing areas in Shanxi province,including the isolation and pathogenicity determination of pathogens,the classification and identification of the main pathogens through morphological identification and EF-1α sequence analysis and the analysis of the dominant pathogen community in different regions and symptoms.At the same time,with the dominant pathogens of Astragalus root rot as the target,multiple screening was conducted of the Bacillus isolated from the rhizosphere soil of Astragalus,in the process of which we obtained 3 Bacillus strains with excellent control effects:R88,R91 and G11.Studies were then made on their inhibition effects on mycelial growth and on the physical and chemical properties of their fermentation broth.The results are as follows:1.The incidence of root rot disease in Shanxi was about 10-30% in general,but reached 60% in seriously affected fields,and the situation was even more serious for trirnnial Astragalus.The dominant pathogens of Astragalus root rot in Shanxi were F.acuminatum、F.solani and F.oxysporum,the isolation frequency of which were 48.88%,28.12%,and 9.58% respectively.The isolation frequency of other strains,including Alternaria sp.,F.redolens and Ilyonectria torresensis,accounted for 13.42%.2.The dominant pathogens of Astragalus root rot differ in different regions of Shanxi.F.acuminatum,F.solani and F.oxysporum took the dominant position in Wuzhai;F.acuminatum and F.solani in Hunyuan and F.acuminatum in Yingxian.The dominant pathogens for different symptoms were also different.For fibriform rot root tissues,the dominant pathogen were F.acuminatum,F.solani and F.oxysporum;for discoloration and shrivel soft rot,mainly F.acuminatum and F.solani;and for the dark and hollow fibrous rot,F.acuminatum and F.solani.Comprehensive analysis results showed that F.acuminatum and F.solani were the most important dominant pathogens of Astragalus root rot in Shanxi provience.3.With F.acuminatum and F.solani as the target respectively,antagonistic Bacillus R88,R91 and G11 were obtained by multiple screening from the150 Bacillus strains isolated from the Astragalus rhizosphere soil.When F.solani was used as the target,the inhibition belt width of the three antagonistic strains in the living body asynchronous confrontation were 7 ±1.26,6.5 ± 1.38 and 3.42±0.97 mm respectively,and the inhibition zone diameter of their bacteria-free filtrate were 20.15 ± 1.37,18.17 ± 1.40 and19.73 ± 2.02 mm respectively.In vitro control test results showed that the disease index of the protective treatment and that of the cure treatment fell within the range of(16.67 ± 8.34)-(46.67 ± 4.70)and(22.22 ± 19.24)-(55.56 ± 9.62)respectively,both showing significant differences(p<0.05)from that of the control(66.67 ± 2.78).When F.acuminatum was used as the target,the inhibition belt width of the three antagonistic strains in the living body asynchronous confrontation were 3.75 ± 1.94,3.92 ± 2.27 and 3.57 ±1.87 mm respectively,and the inhibition zone diameter of their bacteria-free filtrate were 19.96 ± 3.42,20.96 ± 1.85 and 18.92 ± 1.16 mm respectively.The disease index of the protective treatment and that of the cure treatment were in the range of(11.11 ± 9.62)-(50.00 ± 25.00)and(8.33 ± 14.33)-(38.89 ± 9.62)respectively,both showing significant differences(p<0.05)from that of the control(72.22 ± 4.81).4.The bacteria-free filtrate of Bacillus R91,R88 and G11 all showed a significant and lasting inhibition effect to mycelia growth of F.acuminatum and F.solani.Meanwhile,the above 3 strains had good tolerance to temperature,light and p H,which enabled them to adapt to the living environment of Astragalus,and maintain the stability in the antagonistic and control effects.So the antagonistic Bacillus R91,R88 and G11 have great potential for development and application. |
