Screen Of Thermo-Tolerable Strains Of Isaria Fumosorosue And Their Thermo-Tolerance Mechanism Preliminary Analysis

The Isaria fumosorosue was one type of fungal pathogens widely applied in biological control pests at present. The effect of entomogenous fungus was related to its own pathogenicity, and to a large extent affected by the external environmental factors such asultraviolet and temperature.The temperature have an influence on the storage stability of fungal agents, whichwas related to the thermostability. The tolerance of conidia or mycelium to the environment was an important factor in storage and application of conidia, which limited the control efficiency in the field. This study screened the biocontrol strains combining the higher thermotolerance and analyzed the physiological and biochemical properties related to the thermotolerance.Results of this research as follows:1. The spore suspension of seven strains of I. fumosorosue were placed in constant temperature water at 48 ? for 45 min. Then, the spore suspension were cultured for 36h on the single concave slide. The residue viability of each strain after the thermal stress was assessed as an index of its thermotolerance. The results showed that the difference of residue viability of each strain was significant ranging from 28.70%-57.28%. Three strains were of high thermotolerance due to their residue viabilities of>50% but only one strain was weak in thermotolerance due to their residue viabilities of<30%. The residue viabilities of the rest strains fell in a range of 34.72-36.00% and their thermotolerance was thus intermediate.2. The toxicity effect of thermo-tolerance-different strains at the same concentration against wheat aphid was studied with the method of nebulization. The results showed that the 904 strain were the highest virulent strain with the correction mortality of 90.20% and the shortest medianlethaltime.3. The content of hydrophobic protein of strains with different thermotolerance was measured with the BRADFORD method. The result showed that there was significant difference in the content of FAE protein among these strains. The 904 strain with higher thermotolerance had the highest hydrophobic protein. It indicated the relationship between the level of hydrophobic protein with the thermotolerance, which provides a new sight into the study of biological mechanism of strain with the different thermotolerance.4. The activity of SOD enzyme of I.fumosorosue strain with different thermotolerance was determine-d by the way of NBT. The results showed that the activity of SOD enzyme varied significantly with different thermotolerance. The activity of SOD enzyme increased with the rise of temperature. The 904 strain of high enzyme activity in normal atmospheric temperature has higher enzyme activity after heat stress.5. The enzymes electrophoresisd by Native-PAGE andstained by nitroblue tetrazolium(NBT) showed that the strains with different thermotolerance had only one same band, indicating that the tested strains of SOD type of the same kind.6. The trehalose accumulation in I.fumosorosue strain904 dealed with different high temperature stress was studies by the method of anthrone-sulfuric.The results showed that the percentage of trehalose increased with the temperature rising, with heat shock process lasting for 3-6h. However, the percentage decreased when the time of heat stress was above 9h. Under the same conditions, the activity of trehalase was measured by the method of DNS. The trehalase activity varied opposite to the trehalose, which indicated the trehalose accumulation and trehalase activity played an important role in the thermophilic mechanism ofentomopathogenic fungi.