| Bitter gourd wilt is a soil-borne disease,Chemical pesticides are mainly used to control the disease in production,but there are some problems in chemical control,such as pesticide residues,resistance to pesticides and environmental pollution.At present,the pesticides and microbial agents which have good control effect on wilt of watermelon,banana and melon on the market are not ideal for the control of wilt of bitter gourd.Therefore,it is necessary to find a safe and effective control measure.This study is mainly divided into three aspects:(1)Based on the model of soils with high incidence of bitter gourd Fusarium wilt,using fluorescence quantitative PCR and Illumina Miseq high-throughput sequencing platform,and targeting 16S rDNA and ITS genes,the quantitative,diversity,community structure,and vertical distribution of soil enzymes and pH values of Fusarium wilt fungi and soil microorganisms in different depths before and after the application of chemical fumigant metham-sodium were studied.(2)The optimum combination of Pseudomonas chlororaphis G5 strain and fungicide hymexazol(Hym)was screened by pot experiment,and the effects of the combination on defense enzyme activities in bitter gourd leaves were determined.(3)The effects of the best combination of biocontrol bacteria G5 and hymexazol on the control of bitter gourd fumigation and soil enzyme activities were studied in metham-sodium fumigation area.The main results are as follows.In the areas with a high incidence of bitter gourd wilt,the number of Fusarium in the soil layer of 5-40 cm per gram of soil was 10~3-10~4 cfu,and gradually decreased with the increase of soil depth.The number of Fusarium in the 5-30 cm soil layer decreased after metham-sodium fumigation,but there was no significant effect on the number of Fusarium in40 cm soil layer.After fumigation,the 16S rDNA gene copy number of bacteria in soil layer5-30 cm significantly increased,reaching the maximum at 5 cm.The copies of ITS genes in5-30 cm fungi were significantly decreased compared with that before fumigation,and there was no significant difference in the copies of ITS genes in each soil layer,but all of them were significantly higher than that in the soil layer of 40 cm.Beta diversity analysis showed that the community structure of fungi and bacteria in 5 cm and 10 cm soil layers after fumigation was significantly different from that before fumigation treatment.The community structure of fungi and bacteria in soil layers below 20 cm did not change significantly;the soil pH increased in 5-40 cm soil layers;the total activities of urease(S-UE),sucrase(S-SC),catalase(S-CAT),acid phosphatase(S-CAP)in 5-30 cm soil layers were increased.The activity of soil enzymes in 40 cm soil layer was not significantly affected.It was found that strain G5 could colonize in bitter gourd and rhizosphere soil.Plate confrontation test showed that biocontrol bacteria G5 could significantly inhibit the growth of hyphae of bitter gourd Fusarium wilt.The mycelial growth and spore germination of bitter gourd Fusarium wilt fungus were inhibited by different dilution multiples of hymexazol,and the inhibition effect decreased with the increase of dilution multiples.The results of indoor compatibility test between strain G5 and hymexazol showed that hymexazol had no inhibitory effect on biocontrol bacteria G5 at the standard concentration(dilution 4000 times),but could promote the reproduction of G5 in soil.The optimal concentration screening test of biocontrol bacteria G5 and hymexazol compound potted plants showed that the combination of B(1×109 cfu/mL G5 bacterial suspension)and different concentrations of hymexazol had better control effect on bitter gourd wilt than A(1×10~8 cfu/mL G5 bacterial suspension)combined with the concentration of hymexazol.B+0.75Hym(1×10~9 cfu/mL G5 suspension+75%of the standard concentration of hymexazol)The disease prevention effect is 81.60%higher than other treatments,and the combination can significantly increase the stem diameter,plant height,leaf area,dry weight and fresh weight of bitter gourd seedlings.Under the stress of Fusarium oxysporum,B,Hym and B+0.75Hym could induce the increase of PAL,PPO,POD and CAT activities in bitter gourd leaves.Two-year field disease control experiments showed that the control effect of B+0.75Hym on bitter gourd Fusarium wilt was higher than that of B or Hym alone.The results showed that B+0.75Hym,which was selected by pot experiment,could not only prevent and cure bitter gourd Fusarium wilt better,but also reduce the usage of hymexazol.The activities of urease,invertase and catalase in the whole growth cycle of bitter gourd treated with metham-sodium fumigation were higher than those in the non-fumigated treatment.The activities of three soil enzymes in the non-fumigated treatment decreased to a certain extent in 45-60 days,while the activities of three soil enzymes in the fumigated treatment remained high.At 60 days,the control effect of metham-sodium fumigation treatment on bitter gourd Fusarium wilt was 73.86%.The control effect of B+0.75Hym combination on bitter gourd Fusarium wilt was 92.15%.The occurrence of bitter gourd Fusarium wilt was effectively controlled.In conclusion,the application of B+0.75Hym combined with metham-sodium fumigation in bitter gourd wilt area can effectively reduce the incidence of bitter gourd wilt,which has a certain practical value in production. |
