Barley under pressure: combined effects of colonisation by the entomopathogenic fungus Akanthomyces muscarius and the bird cherry oat aphid Rhopalosiphum padi

Abstract

Entomopathogenic fungi are increasingly considered for use as biological control agents. However, their effects in tripartite systems involving plants, herbivorous insects, and endophytic fungi remain context dependent and poorly understood. In this study, we tested the hypothesis that inoculation of barley with the entomopathogenic fungus Akanthomyces muscarius affects the biomass of aphids feeding on the plants and influences barley seedling size at early developmental stages. Seedling apical meristems of two barley cultivars, Golden Promise (GP) and Laureate (L), were inoculated with the fungus and subsequently exposed to feeding by the bird cherry-oat aphid Rhopalosiphum padi. Plant dry biomass and total aphid biomass per plant were measured at the end of the experimental period. Inoculation with A. muscarius did not significantly reduce total aphid biomass on either barley cultivar. By contrast, fungal inoculation significantly reduced seedling dry biomass in GP, whereas no such effect was detected in L. Linear mixed-effects modelling revealed significant effects of cultivar, inoculation, and their interaction on plant biomass, indicating cultivar-dependent plant responses to fungal colonisation. Total aphid biomass was significantly affected by cultivar but showed no consistent response to fungal inoculation. This study provides a controlled evaluation of a barley-A. muscarius-aphid tripartite system and highlights cultivar-specific outcomes of fungal inoculation under aphid feeding pressure.