Studies On The Relationship Between Thermotolerance And Hydrophobin-like Proteins In Aerial Conidia Of Isaria Fumosorosea

The entomopathogenic fungus, Isaria fumosorosea, is a main biocontrol against whitefly, Bemisia tabaci (Gennadius). Because Bemisia tabaci occurred in high temperature, high temperature is one of the key factors influencing its application. The hydrophobin-like proteins on conidial wall are likely related to conidial thermotolerance. To determine a role of proteins on condial wall in its thermotolerance and the relationship between hydrophobin-like proteins and the conidial thermotolerance. We studied the thermotolerance and adhesion of conidia on hydrophobin-like proteins, mainly including the survival ratio of conidia, the number of adhered conidia, contents of hydrophobin-like proteins under the thermal stress temperature, and their relationship, which will provide for its range of high temperature in the field.Our results showed that when temperature ranged between36℃and44℃, Isaria fumosorosea conidia could still survived, and the survival ratio of conidia decreased gradually with increasing of the thermal stress temperature and time. The median lethal time Lt50and median lethal temperature LT5o were estimated by survival ratio of conidia. When exposure to36℃、38℃、40℃、42℃、44℃and46℃of the thermal stress temperature, the Lt50were estimated as4.43h、3.7h、1.82h、1.05h%0.15h and0.07h, respectively. When exposure to0.5h、.0h、1.5h、2.01、2.5h and3.0h of the thermal stress time, the LT50were estimated as42.9℃、41.4℃、40.4℃、39.5℃、38.8℃and38.3℃、respectively. The Lt50and LT50were significantly negatively correlated with the temperatures and time, respectively.The number of conidia adhering to B. tabaci pupa over different thermal stress time at six thermal stress temperatures differed significantly. The number of adhered conidia did no differ among0.5h to1.5h at36℃to40℃.They decreased gradually with increasing of the thermal stress time compared with the control group. However, the number of adhered conidia decreased gradually with extension of the thermal stress time between42℃and46℃of the temperature.The contents of hydrophobin-like proteins from cell wall differed significantly among six thermal stress temperatures. There was no significant difference among different thermal stress time at36℃of the temperature, and the protein contents decreased gradually over different time at38℃-46℃of the temperature. However, the SDS-PAGE analysis of hydrophobin-like proteins from cell wall showed no significant difference among the treatments, the main strip is about15.0kDa.There was no significant correlation among the survival ratio of conidia, the number of adhered conidia, hydrophobin-like proteins contents at36℃of the temperature. As increase of the temperature, there were a positive exponent correlation between conidial survival ratio and adhered conidial number at different stress temperatures. When temperature rised, protein contents significantly affected conidial survival ratio and adhered conidial number, thus indicating that conidial thermotolerance has a positive correlation with protein contents. These results reflect the microecological relationship of Isaria fiimosorosea from biochemical and ecological level and provide theoretical basis for improving its biocontrol effect.