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

Authors: RAMAKUWELA, TSHIMANGADZO - Agricultural Research Council Of South Africa; HATTING, JUSTIN - Agricultural Research Council Of South Africa; Bock, Clive; Vega, Fernando; WELLS, LENNY - University Of Georgia; MBATA, GEORGE - Fort Valley State University; Shapiro Ilan, David

Submitted to: Biological Control
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/16/2019
Publication Date: 10/27/2019
Citation: Ramakuwela, T., Hatting, J., Bock, C.H., Vega, F.E., Wells, L., Mbata, G.N., Shapiro Ilan, D.I. 2019. Establishment of Beauveria bassiana as a fungal endophyte in pecan (Carya illinoinensis) seedlings and its virulence against pecan insect pests. Biological Control. https://doi.org/10.1016/j.biocontrol.2019.104102.
DOI: https://doi.org/10.1016/j.biocontrol.2019.104102

Interpretive Summary: Chemical pesticides can cause harm to humans and the environment. Therefore, it is important to explore non-chemical methods to control pests in agriculture. One option is to use insect-killing fungi to control insect pests. The insect-killing fungus called Beauveria bassiana can be applied using regular agricultural spray equipment. This beneficial fungus can also live inside certain plants. When a fungus or other organism (such as a bacterium) lives inside a plant it is called an endophyte. Our goal was to find out if the beneficial fungus could be inoculated into a pecan tree to live as an endophyte. We succeeded in inoculating the beneficial fungus into pecan seedlings by soaking seeds in the fungus, rolling seeds in the fungus, or drenching the seedling. Presence of the fungus in the plant was confirmed by molecular methods and by re-isolating the fungus from the seedling. The fungus remained capable of killing insects when living inside the tree. In a lab study, we discovered that the fungus in its endophytic form (inside the tree) could reduce pecan aphid populations. Pecan aphids are serious pests of pecan. This study indicates potential for a new and safe method to reduce pest population in pecan.

Technical 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. Subsequently we explored whether the established endophytic fungus suppressed pecan insect pests. 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 three susceptible insect hosts (Curculio caryae, Galleria mellonella and Tenebrio molitor). Moreover, in a leaf-disc assay, populations of two pecan aphids (Melanocallis caryaefoliae and Monellia caryellaI) 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.