Establishment of Beauveria bassiana as a fungal endophyte in pecan (Carya illinoinensis) seedlings and its virulence against pecan insect pests

Abstract

Pecan (Carya illinoinensis) is an important crop in the USA, which produces approximately 55% of the world’s pecans. Several insect pests and various plant diseases reduce crop yield directly destroying nutmeats, or indirectly through effects on foliage and shucks, reducing photosynthesis. Beauveria bassiana is a well-studied, commercialized fungal entomopathogen that when applied inundatively is an effective biocontrol agent against certain pecan pests. In addition to being used in inundative biocontrol, B. bassiana can exist as an endophyte in many plant species and has been shown in some cases to reduce pest damage when present as an endophyte. The potential for B. bassiana to exist as an endophyte in pecan had not been explored previously. We tested whether B. bassiana could endophytically colonize pecan seedlings by seed soaking, seed coating and soil drenching. Results indicated that B. bassiana became established in the roots, leaves and stems of pecan seedlings. Establishment was verified using molecular techniques as well as completing Koch’s postulates on the re-isolated fungus, infecting two susceptible insect hosts (Galleria mellonella and Tenebrio molitor) and a target pest (Curculio caryae). Subsequently we explored whether the established endophytic fungus suppressed two pecan aphid species. In a leaf-disc assay, populations of two pecan aphids (Melanocallis caryaefoliae and Monellia caryella) were reduced when placed on leaves of pecan that were colonized endophytically with B. bassiana, relative to control leaves. Our study demonstrates the ability to establish endophytic B. bassiana in pecan and the potential to apply this capability in pecan pest management. Additional research is needed to determine the utility of the endophytic approach against various insect and plant pathogens and to measure efficacy under field conditions.