Molecular characterization of Beauveria bassiana, mycovirus detection and their potential use for aphid biocontrol in Costa Rica

Beauveria bassiana is an entomopathogenic fungi used for biocontrol of insects, and although current commercial products are available, further improvement is needed. The aim of this project was to characterize a small collection of local isolates using gene-specific (ITS) and SSR molecular markers, and testing for the presence of mycoviruses, as well as pathogenicity assays onto Toxoptera citricida. Preliminary ITS sequence data identified 21 isolates as Beauveria bassiana and one as Cordyceps bassiana teleomorph (B9 strain). A phylogentic tree was inferred using maximum likelihood (ML) method. The greatest number of samples (19) clustered with B. bassiana from Latin America, two samples (B27 and B31) clustered with isolates from the USA, Australia and Asia, while, one sample (B23) was separated from all other strains as supported by a 98% bootstrap value. Preliminary SSR data showed great diversity among the isolates. Additionally, dsRNA bands, indicative of mycovirus presence, were detected in six out of 18 isolates. Pathogenicity bioassays were done on ten aphids T. citricida per experimental unit using detached sweet orange leaves submerged for 1 min in a 10⁷ conidial suspension. Two isolates showed pathogenicity toward T. citricida (Ps < 0.05). However, high variation between independent experiments (P < 0.05) and mortality due to contaminating fungi in control individuals were observed. Studying this collection will help further understand the applicability of these isolates to control insects and improve biological control using local organisms.