| Soybean Cyst Nematode(SCN),a soil-borne endoparasitic plant nematode,is one of the most important pathogens in the production of soybean(Glycine max(L.)Merrill.SCN occurs worldwide,causing economic losses up to US$3 billion per year.In this paper,parasitic fungi were isolated and purified from cysts,eggs and second-stage juveniles of SCN in different seasons in Qingyang and Pingliang,Gansu Province.Morphological and molecular biology methods were used to identify and calculate the frequency of isolation.Seventeen of these strains and four strains preserved in the laboratory were selected to explore their effects on nematodes,control effect in vitro and control effect The conclusions are as following.1.366 strains of fungi were isolated and purified from SCN collected in spring,summer and autumn,and identified as 11 genera.The isolation frequencies of Fusarium,Pochonia,Aspergillus and Purpureocillium were highest,respectively were 30.60%,24.04%,17.21% and 13.66%.The isolation frequencies of Alternaria,Penicillium,Ilyonectria and Humicola were lower,respectively were 4.64%,3.00%,2.46% and 1.91%.The isolation frequencies of Chaetomium,Paraphoma and Cladosporium were 0.82%.In spring,summer and autumn,the dominant parasitic fungi of cyst nematode were Pochonia chlamydosporia,Fusarium solani,Purpureocillium lilacinum,Aspergillus fumigatus and F.fujikuroi.Ilyonectria macrodidyma was isolated in summer and autumn.Cladosporium sp.is sporadic species in spring.Paraphoma chrysanthemicola is sporadic species in summer.Chaetomium thermophilum is sporadic species in autumn.2.The parasitic effects of spore suspension on SCN eggs,the inhibiting effect of spore suspension and fermentation liquid on egg hatching and the lethal effect on J2 were determined to explore the modes of action.The results showed that egg parasitism rates of 10 strains were over 70.00%.Inhibiting rates of 7 strains were over 65.00% and mortality rate of 4 strains on J2 were over 30.00%.3 biocontrol fungi,Aspergillus sp.A1,A.parasiticus AP2 and A.fumigatus AF7 with better effects were used for further research.Further studies showed that the action modes of 3 biocontrol fungi were the fermentation brothes inhibited egg hatching and caused death of J2,spore suspensions parasited on eggs and inhibiting egg hatching.The lethallty rate of A1 fermentation to J2 and inhibiting rate on eggs were 90.01% and 68.75%,and the parasitic rate and inhibiting rate on eggs of spore suspensions were 70.05% and 61.90%,but lethallty rate of spore suspension to J2 was 29.63%.The lethallty rate of AP2 fermentation to J2 and inhibiting rate on eggs were 80.03% and 67.19%,the parasitic rate and inhibiting rate on eggs of spore suspensions were 79.50% and 76.09%,but lethallty rate of spore suspension to J2 was 25.40%.The lethallty rate of AF7 fermentation to J2 and inhibiting rate on eggs were 86.74% and 75.00%,the parasitic rate and inhibiting rate on eggs of spore suspensions were 81.33% and 75.00%,but lethallty rate of spore suspension to J2 was 30.69%.3.The control effects of pot experiment on SCN showed that among A1,AP2 and AF7,AP2 had the best control effect,and the of control effect of fermentation broth was better than that of wheat bran culture.The cyst reduction rates of A1,AP2 and AF 7 treated with 1× solution were the highest,48.62%,59.63% and 50.46%,respectively.Soybean root length increased by 49.76%,29.76% and 63.28%,plant height increased by 56.35%,50.27% and 17.22%,respectively.The cyst reduction rates of A1,AP2 and AF7 treated with 3% wheat bran culture were 46.08%,53.92% and 49.10%,respectively.Soybean root length increased by 24.20%,29.32% and 21.00%,plant height increased by 30.99%,42.71% and 65.20%,respectively.With the increase of the dosage of wheat bran culture and the concentration of fermentation broth,the rate of cyst degeneration increased. |
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