Study of Beauveria bassiana growth, blastospore yield, desiccation-tolerance, viability and toxic activity using different liquid media

Beauveria bassiana was grown on three liquid media containing casaminoacids, corn steep liquor or peptone. After incubation, the blastospore counts reached 6.38 × 109 blastospores/ml, in the medium containing sucrose and corn steep liquor, which was significantly higher than the obtained with media containing casaminoacids or peptone. The medium containing corn steep liquor produced predominately submerged conidia, meanwhile the other media produced blastospores. The blastospores produced in the medium containing casaminoacids presented faster germination rates, than the blastospores produced in media containing corn steep liquor or peptone, although, after airdrying, were observed significant reductions on the viability of blastospores produced in the media composed by casaminoacids or peptone, but the spores produced in the medium with corn steep liquor were not affected. For storage of blastospores at 4 and 26°C after some months, the blastospores produced in the medium with casaminoacids showed the highest viability at 26°C, whereas at 4°C the counts of viable blastospores produced in medium containing corn steep liquor were significantly higher than the counts of blastospores produced in the other media with casaminoacids or peptone. The blastospores maintained for six months at 4°C showed high mortality against third-instar Plutella xylostella larvae.Key words: Beauveria bassiana, liquid media, fermentation, short times of propagation, biological control, entomopathogen fungus

Antagonistic activity of selected strains of Bacillus thuringiensis against Rhizoctonia solani of chili pepper

The aim of this work was to determine, in vitro, the antagonistic effectiveness of 60 strains of Bacillus thuringiensis against damping-off and root and stem rot caused by Rhizoctonia solani. The strains wereobtained from the International Collection of Entomopathogenic Bacillus at the FCB-UANL. During the in vitro dual culture assay only 16 of the strains displayed an inhibitory effect. Six strains were chosen to bescreened simultaneously by volatile antibiotics, thermostability and seedling assay. In the volatile antibiotics assay, the strains GM-11 and GM-121 showed the best inhibitory effect over R. solani growth.None of the strains showed an efficient antagonistic effect during the thermoestability assay. In seedling assay, majority of the antagonistic isolates, GM-23, GM-11and GM-121, were effective in the reduction of R. solani infection. In addition, GM-23 increased the length of pepper seedlings. These results suggest that the B. thuringiensis strains studied have an excellent potential to be used as bio-control agents of R. solani in chili pepper