Endophytic Establishment of Fungi As an Unintended Consequence of Biocontrol with Fungal Entomopathogens

The fungus Beauveria bassiana has been used as an entomopathogenic biocontrol agent of important insect pests around the globe for several decades. Several strains and formulations are commercially available. In addition to its ecological role as an entomopathogen, B. bassiana can also colonize and live within plants as an endophyte. ,Endophytic colonization has been demonstrated in multiple plant species including Gossypium hirsutum, typically under lab conditions using special inoculation methods. We tested if a simple, conventional foliar application of a commercially formulated B. bassiana would result in successful endophytic colonization of cotton plants under normal greenhouse conditions. Cotton plants at the third true leaf stage were treated with Botanigard 22 WP (dosage rate of 2 lb/100 gal) using a handheld sprayer until the point of runoff. Leaf samples were taken at 1, 7 and 14 days after spraying. Results showed that plants were widely colonized at 1 and 7 days after inoculation. At day 14, only 40% of the plant tissues were still positive for endophytic B. bassiana. In addition, preliminary results using the same foliar application under field conditions also confirmed endophytic establishment of B. bassiana in cotton. Taking together, our results provide evidence of endophyte establishment as part of the normal life cycle of commercially available B. bassiana when employed as an insect biocontrol agent. The ecological consequences of this largely overlooked non-target effect on insect-plant interactions remains to be investigated.