A Preliminary Study On The Antifungal Mechanism Of HSAF From Lysobacter Enzymogenes OH11 Against Wheat Scab(Fusarium Graminiarum)

HSAF is a heat stable antifungal factor isolated from Lysobacter enzymogenes strain OH11.It specially inhibits a wide range of filamentous fungi and oomycetes but lacks the inhibitory activity to bacteria and Saccharomyces cerevisiae.Previously studies showed that HSAF might directly inhibit sphingolipid synthesis which results in cell wall thicking,disrupting polarity growth of mycelia.However,this mechanism is just a speculation,which lacks direct evidence.Thus,it's a significant for us to further study the mechanism of HSAF's antifungal activity to develop HSAF as antifungal agent..In this study,we detectded the antagonistic activity of HSAF against 10 fungal pathogen strains and 1 oomycetes pathogen.The results showed that HSAF had inhibitory activity to all of the 11 pathogenic strains with different degrees.It had the strongest inhibitory activity to Valsa pyri,Magnaprothe oryzae and Sclerotinia sclerotiorum,which 50%effective concentration(EC50)of HSAF against these three strains were 0.5 ?g/mL,0.7 ?g/mL and 0.8 ?g/mL respectively and the 95%effective concentration(EC95)of HSAF against them were 9.1 ?g/mL,2.2 ?g/mL and 6.3 ?g/mL respectively.These data showed that HSAF has potential value to control fungal plant disease and maybe it can be mainly used in V.pyri,M.oryzae and S.sclerotiorum controling.After treatment with HSAF,not only the conidia germination,mycelial growth and conidiation of F.graminearum PH-1 were inhibited,but also it could exhibit abnormal morphology such as curling,tip splitting and tip swolling of mycelia and more germination spots,swollen germ tube and extensive branching of germling.Meanwhile,HSAF possessed stronger inhibitory activity to germination of conidia,which indicated that HSAF could disturb polarized growth of PH-1 and maybe energy meatbolism of PH-1 is also influenced.TEM analysis showed that HSAF could lead to malformation of subcellular morphology involving plasmolysis,invagination of plasmalemma and more lipid bodies.In the presence of 5 ?g/mL HSAF,PH-1 exhibited hypersensitivity to osmotic stress,cell membrane stress and cell wall stress factors.These data showed that HSAF could reduce PH-1's resistance to some exeprimental stress factors,and it might effect PH-1 as an osmotic stress factor.Compared with treating with HSAF,F.graminearum mostly exhibited curling of hyphae and more branching beside tip of hyphae after treated with Carbendazim,which was different from that HSAF could cause tip swelling of hyphae additional.Thus HSAF has different antifungal mode from Carbendazim.