Shumaila Rasoo , Nanna H. Vidkjær , Kourosh Hooshmand , Birgit Jensen , Inge S. Fomsgaard
Entomopathogenic fungi (EPF) can display a plant-associated lifestyle as endophytes. Seed
application of EPF can affect insect herbivory above ground, but the mechanisms behind this
are not documented.
Here we applied three EPF isolates, Beauveria bassiana, Metarhizium brunneum and
M. robertsii, as seed inoculation of wheat and bean, and evaluated the effects on population
growth of aphids, Rhopalosiphum padi and Aphis fabae, respectively. In wheat and bean
leaves, we quantified benzoxazinoids and flavonoids, respectively, in response to EPF inoculation
and aphid infestation to elucidate the role of specific plant secondary metabolites (PSMs)
in plant–fungus–herbivore interactions.
Inoculations of wheat and bean with M. robertsii and B. bassiana reduced aphid populations
compared with control treatments, whereas M. brunneum unexpectedly increased the
populations of both aphids. Concentrations of the majority of PSMs were differentially altered
in EPF-treated plants infested with aphids. Changes in aphid numbers were associated with
PSMs regulation rather than EPF endophytic colonisation capacity.
This study links the effects of EPF seed inoculations against aphids with unique PSM accumulation
patterns in planta. The understanding of PSM regulation in tri-trophic interactions is
important for the future development of EPF for pest management.