The Research On Surfactant’s Screening And Its Synergism For Isaria Fumosoroseus

Isaria fumosoroseus is one of the most important entomogenous fungi.Its pathogenicity can be facilitated by increasing the number of spores and gemma on the surface of target plants and target pests.Increasing the adhered amount of spore and gemma can be achieved by two approaches.One is to reduce the surface tension of spore suspensions of Isaria fumosoroseus,the other is to decrease the contact angle of suspensions with the insect surface.Surfactant is a significant additive that can effectively reduce the surface tension of medicinal solution and improve the utilization rate of pesticides.In this dissertation,the synergistic effect of different surfactants into spore suspension of Isaria fumosorosea and the safety evaluation of Isaria fumosorosea conidia from surfactants were evaluated.Scanning electron microscopy(SEM)was used to observe the amount of surfactant-added Isaria fumosorosea conidia which was attached on the body wall of Plutella xylostella larvae,and the influence of surfactant on the virulence of Plutella xylostella larva.The results are as following:1.The surface freeenergy of leaves of cabbage,apple,eggplant and cucumber was measured by OWRK method.When 4 different surfactants were added respectively into spore suspension of Isaria fumosorosea,the surface tension and critical micelle concentration(CMC)of each solution are determined by surface tension method,The results showed that the surface free energy of cabbage,apple,eggplant and cucumber leaves were 28.24,29.26,45.21 and 66.79 m J/m~2,when the mass concentration of Pullulan and OFX-0193 reached 500 mg/L,and the mass concentration of AOS and Nekal reached 250 mg/L,the critical micelle concentration(CMC)is reached,the surface tension of the spore suspension is reduced to45.60,27.30,24.30,and 21.80 m N/m,which OFX-0193,AOS,and Nekal reach the critical micelle concentration surface.The tensions are all less than the surface free energy of the four tested leaves,indicating that the three surfactants can significantly improve the wetting properties of the liquid at appropriate concentrations.2.The surface tension and critical micelle concentration(CMC)of each solution are determined by surface tension method,and their contact angle and maximum retention(Rm)on plant leaves were measured by goniometry and weight difference method.The results showed that the wetting ability of Isaria fumosorosea spore suspension on 4 types of tested plant leaves are improved when adding the concentration of 125-500 mg/L of OFX-0193,AOS and Nekal.Nekal(250 mg/L)functioned best with its Rm(11.90±0.23)and(13.28±0.28)mg/cm~2 and contact angle(29.5°,27.5°)on cabbage and apple leaf surfaces,indicating it outperforms in promoting wetting ability of Isaria fumosorosea PF904.OFX-0193 showed the best maximum retention of 9.45 mg/cm~2 on eggplant leaf surface at the concentration of 125mg/L.3.Safety assessment of these screened surfactants had also been conducted.The results of inhibition rate of spore germination measurement showed Nekal and OFX-0193 do not restrain Isaria fumosorosea PF904 germination,but AOS do.In conclusion,surfactants of Nekal and OFX-0193 can be employed to assist Isaria fumosorosea to protect apple and cabbage from pests,OFX-0193 can also be used to control eggplant pests.4.The amount of conidia attachment to the body wall of Plutella xylostella,and the infestation rate and virulence to Plutella xylostella were examined under different concentrations of OFX-0193 and Nekal surfactants in Isaria fumosorosea.The results showed that the conidia attachment number of the spores of Plutella xylostella larvae in the larvae of Plutella xylostella and the chances of infection can be raised remarkably when adding Nekal(250 mg/L)and OFX-0193(125 mg/L).The amount of spores attached to the spore suspension of Plutella xylostella larvae was 2.19 times,1.78 times,and 1.94 times of the control,which increased the probability of infection.Besides,spore germination time was reduced greatly,promoting the formation of appressoria and increasing the infection rate.The results of the virulence test showed that: the addition of Nekal(250 mg/L)and OFX-0193(125 mg/L)can significantly increase the pathogenicity to Plutella xylostella larvae.The addition of Nekal spore suspension made the corrected mortality of diamondback moth larvae reach to 79.2%,the median lethal time(LT 50)reduced to 2.71 d,It has a significant synergism.