Influence of the plant interacting entomopathogenic fungus Beauveria bassiana on parasitoid host choice-behavior, development, and plant defense pathways.

Rasmus Emil Jensen,Annie Enkegaard,Tove Steenberg,Carmina Cabral,Alejandro Carlos Costamagna

doi:10.1371/journal.pone.0238943

Abstract

Inoculating plants with entomopathogenic fungi may influence plant nutrient uptake and growth, and herbivore performance. Knowledge is limited concerning the effects of this symbiosis on higher trophic levels. We examined how fungal treatment of faba bean seeds with the entomopathogenic fungus Beauveria bassiana influenced the choice-behavior and development of the aphid parasitoid Aphidius colemani. We also sampled plant material for analysis of changes in expression of genes related to plant defense pathways. While parasitoids were compatible with plants inoculated with B. bassiana initially (66 vs. 65% parasitization on inoculated and control plants, respectively; similar development times of parasitoids: 9.2 days), the emergence of adult parasitoids originating from aphids on fungus treated plants was significantly lower (67 vs. 76%, respectively). We also found that the defense response changed, similar to induced systemic resistance, when plants were treated with B. bassiana, similarly to what has been found for other plant symbiotic microorganisms. These novel findings show that although the application of entomopathogenic fungi to plants can alter the plants’ defense against herbivores, it may also have an impact on beneficial insects, so their function and use should be evaluated on a case-by-case basis.

Highlights

Terrestrial plants shelter fungi that live as endophytes inside plant tissue
We have shown the effects of a plant-fungal interaction obtained via seed treatment without focusing on the location of the fungus inside the plant
Very little is known of how entomopathogenic fungi (EF) colonize plants [13], and our results emphasize that interactions manifest themselves after treating the seed with a spore solution

Summary

Introduction

Terrestrial plants shelter fungi that live as endophytes inside plant tissue. Endophytism has become synonymous with mutualism; the ecological role of endophytes can be complex and imbalanced [1, 2]. Endophytic fungi can improve growth and plant resistance to herbivores, pathogens, and various abiotic stresses and may have extensive effects on populations of herbivores and their natural enemies [2,3,4,5]. While most endophyte research has focused on the obligate ascomycete grass endophytes producing toxic alkaloids, species of entomopathogenic fungi (EF), another group of hypocrealan ascomycetes, have more recently been identified as plant colonizers [6, 7].

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