The pathogenicity of Beauveria bassiana: what happens after an endophytic phase in plants?

: The banana weevil Cosmopolites sordidus (Germar) (Coleoptera: Curculionidae) is a serious constraint to banana (Musa spp.) production throughout the world. The entomopathogenic fungus Beauveria bassiana (Balsamo) Vuillemin (Ascomycota: Hypocreales) offers a potential weevil management option, but conventional delivery mechanisms have limited its success. As an endophyte, however, B. bassiana can be efficiently delivered to banana planting materials for the potential management of C. sordidus. However, entomopathogens can change morphology and efficacy against their target host when successively sub-cultured on artificial media or when exposed to certain physical and chemical environmental conditions. Whether such changes occur in B. bassiana after an endophytic phase inside a banana plant remains unknown. The primary aim of our study was to evaluate the viability, growth, sporulation and pathogenicity of endophytic B. bassiana. To attain this, two sets of experiments, namely morphological characterization and larval bioassays, were conducted under laboratory conditions. In these experiments, growth and pathogenicity of the wild-type B. bassiana strain G41, obtained originally from banana farms, was compared with the endophytic B. bassiana strain G41, re-isolated from the rhizome of B. bassiana-inoculated banana plants at one month post-inoculation. Morphological characterization, conidial germination, colony growth and sporulation rate was assessed on SDAY media while pathogenicity was determined 15 days after immersing the larvae of C. sordidus in different conidial doses. No differences were observed in colony appearance and growth rate between the endophytic and wild-type strain. Percentage conidial germination for the endophytic strain (91.4-94.0%) was higher than for the wild-type (86.6-89.7%). LD50 equated 1.76 x 10(5) and 0.71 x 10(5) conidia/ml for the wild-type and endophytic B. bassiana strains, respectively, but did not differ between strains. Our study demonstrated that, after an endophytic phase inside the banana plant, B. bassiana retains it morphology and pathogenicity against the banana weevil larvae; and thus can offer protection against the damaging larvae feeding inside the rhizome.