Abstract:
Mycoviruses have been reported in a large numbers of fungal species, sometimes affecting their growth and pathogenicity. Beauveria is soil ascomycete which can kill a wide range of insect pests and it is used as a biological control agent of insect pests. Mycoviruses have been found in many isolates of Beauveria, but little is known about the effects of mycoviruses on the pathogenicity of Beauveria. The aim of this study was to determine the presence/absence of mycoviruses in Beauveria isolates and evaluate the effects of mycoviruses on the pathogenicity of Beauveria to insect pests. The results of this study could help us improving the knowledge about mycoviruses and selecting more effective Beauveria strains as biocontrol agents. Five B. bassiana and one B. caledonica isolates from New Zealand were tested for the presence of dsRNAs which are indicative of virus presence. Five out of six isolates contained at least 2 different sized dsRNAs. Sequencing of dsRNAs from B. bassiana isolates #5539 and #5541 detected a presumed new Amalgavirus. The relative growth rates, sporulation and dsRNA sizes of these six Beauveria isolates and their effects on the pathogenicity to model insects (mealworms and waxworms) were examined. While growth rates and sporulation were correlated to each other, there was no obvious correlation between in-vitro growth rates and the numbers and sizes of dsRNAs in the different Beauveria isolates. In addition, the effects of dsRNAs on in-vitro growth rates did not mirror the virulence level of the same fungal isolates in insect assays. In order to examine the effects of mycoviruses on individual Beauveria cultures, dsRNAs were eliminated from B. bassiana isolates #6887 and #5539 by cycloheximide treatment. In insect assays, the virulence of #6887 virus+ and viruswas almost the same, while the original #5539 isolate was slightly more virulent than #5539 cycloheximide cured isolate.
