Evolutionarily informative strain-typing for Beauveria bassiana: multilocus haplotype stability and a genetic context for the mycoinsecticide GHA

Authors: Rehner, Stephen; RIVERA, YAZMIN - Animal And Plant Health Inspection Service (APHIS); Jaronski, Stefan

Submitted to: Journal of Invertebrate Pathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/15/2017
Publication Date: N/A
Citation: N/A

Interpretive Summary: Although some fungi can be used as biocontrol tools for reducing the billions of dollars of damage caused annually by insects, one problem with the use of biocontrol fungi is that their effectiveness and ability to persist in the environment is not well known. Evaluating this effectiveness and persistence requires precise identification tools to distinguish released strains from related fungi that naturally occur in the environment. In this study, a combination of novel genetic markers was developed that uniquely distinguishes strain GHA of the widely applied insect fungal pathogen Beauveria bassiana. These diagnostic genetic markers are shown to be stable and have remained unchanged in GHA throughout 30 years of cultivation and industrial production. These results are significant because they provide robust methods for identifying and tracking the fate of this important insect biocontrol agent. These genetic markers will be used by insect pathologists and mycologists investigating and implementing insect pest management programs for field crop pests.

Technical Abstract: Beauveria bassiana strain GHA (ARSEF3620, ATCC74250), the active component of mycoinsecticide formulations BotaniGard® and Mycotrol® (Certis, Columbia, MD), is a leading fungal biocontrol agent used against pest insects. Due to its pathogenicity and virulence toward diverse insect taxa, GHA is often used as an experimental treatment or comparative standard in field and in vitro bioassay research. To facilitate the identification and evolutionary analysis of GHA, its multilocus genotype combining Bloc nuclear intergenic DNA sequence, microsatellite and mating type marker data was determined and shown to be unique among diverse B. bassiana isolates. The GHA haplotype has remained invariant throughout its ~30 years of commercial production. A sequence-typing system based on the Bloc nuclear intergenic region representative of diversity detected in a global screening of >3200 isolates is proposed for diagnosis of phylogenetic diversity within B. bassiana. Currently, 18 divergent terminal lineages are recognized and given ad hoc designations, A1-A18, with GHA constituting lineage A4. Thirty-eight A4 lineage individuals were identified in the global Bloc diversity survey, all of which are genotypically different from GHA. Cosmopolitan in distribution but nowhere abundant, the A4 lineage was most frequently isolated and genotypically diverse in western North America, where it includes individuals of both mating types. However, Index of Association tests indicate these individuals are in linkage disequilibrium, and thus non-recombining. The combination of molecular markers used here enable both strain-level discrimination of GHA and other B. bassiana individuals and establish a common genetic framework for ongoing evolutionary investigation of B. bassiana.