Biocontrol potential of endophytes of healthy Castanea dentata tissue for application against Cryphonectria parasitica

Abstract

The American chestnut, Castanea dentata (Marsh.) Borkh., was devastated by an exotic fungal pathogen, Cryphonectria parasitica (Murr.) Barr., introduced in the early 1900’s. Restoration of C. dentata is desirable for ecological and economic reasons. Endophytes, organisms that reside within host plant tissue without causing symptoms, may be a reservoir for sources of biological control agents (BCAs) active against C. parasitica. To evaluate this potential resource, endophytes were isolated from C. dentata stem sections. These were each screened in in vitro, dual-culture competition tests against four virulent C. parastica isolates and objectively assigned to antagonism classes. Of 109 endophytes screened, 84 (77%) showed some degree of antagonism against C. parasitica. Of the top ranked endophytes 10 of 24 tested were shown to excrete antibiotic substances active against C. parasitica. Microscopy failed to reveal any direct mycoparasitism among these top endophytes. Four of the top 18 endophytes were capable of colonizing a pre- established lawn of C. parasitica. The internal transcribed spacer (ITS) of these top performing endophytes was sequenced and each species putatively identified with Basic Local Alignment Search Tool (BLAST). The results of these experiments suggest several endophytes, particularly NC3K (Sordariomycetes), are candidates for further research and potential application as BCAs active against C. parasitica.