Tolerance Of Beauveria Bassiana Isolates From Different Regions Of China To Stress Of Temperature And Humidity

Beauveria bassiana is one of the most common entomopathogenic fungus, and its conidial preparations have been widely used against various crop and forest pests. Temperature and humidity are important factors on conidial germination and infectivity, as well as storage stability and field efficacy. The fungus distributes globally, with varying thermal and humid response for different strains. The relationship of the fungus and the other to temperature and humidity has been intensively studied, but is still not completely known, especially the relation of the thermal and humid preferance to their georgraphic origins. To study the thermal and humid tolerance with relation to geographic origin, the response of98isolates from14provinces to43℃thermal stress wes tested and their drought tolerance, growth rate and sporulation at17℃,24℃and31℃were compared.Thermal stress to the conidial powder of various isolates was made by putting the powder into water bath at43℃for30m, with the germination rate of survived conidia to the rate of the non treated conidia as control as the thermal tolerance index. The result showed that the tolerance index of the tested isolate varied between0.09-0.98with extremely significant difference (P<0.01). The tolerance of7stressed isolates was above0.90, showing high tolerance. Besides, the tolerance of49isolates was above0.50. AN OVA indicated that thermal tolerance between the14provinces was not significantly different. The tolerance of the tested isolates did not vary regularly with their geographic location. Correlation analyses between thermal tolerance to latitude, annual mean temperature and annual rainfall revealed that the variation of the tolerance was not obviously related.The conidial suspension of each isolate was spread onto a2%water agar slide and was incubated at combinations of different temperatures and different humidity’s. The result showed that under the3temperatures, drought tolerance of the isolates varied between-12.56～-1.13,-11.72～-1.02and-1.57～-13.10. The difference of the drought tolerance differed significantly. At17℃, the average tolerance of the7Anhui isolates was the highest, that of Ningxia was the lowest, while there was no obvious difference between those of the other provinces. Under24℃, the tolerance of Inner Mongolia was significantly different to those of Guangdong, Guangxi and Hunan, with the highest at Hunan and the lowest at Guangdong. Under31℃, only those of Anhui (the highest) and Guangdong (the lowest) was significantly different and the differences between the other provinces were not significant. All these suggest that the tolerance of the drought tolerance of the provinces was not significantly different, but the difference between the isolates from the same province was significantly different.The isolates were incubated for test of growth rate and sporulation, respectively under different temperatures. The result showed that the growth rates of the isolates were0.64～2.53,0.87～4.30and0.45～4.03, respectively at the3temperatures. The sporulation under the3temperatures. The correlation analyses between growth rate and sporulation, respectively at different temperatures, was not significantly correlated to latitude, annual mean temperature and annual rainfall.