Sipha maydis sensitivity to defences of Lolium multiflorum and its endophytic fungus Epichloë occultans

MARTÍNEZ-GHERSA, MARIA ALEJANDRA; NEWMAN, JONATHAN A.; MACE, WADE J.; GUNDEL, PEDRO E.; BASTÍAS, DANIEL A.; CARD, STUART D.

PeerJ

PeerJ

Lugar: California; Año: 2019 vol. 7 p. 2 - 21

Background. Plants possess a sophisticated immune system to defend from herbivores.These defence responses are regulated by plant hormones including salicylic acid(SA) and jasmonic acid (JA). Sometimes, plant defences can be complemented bythe presence of symbiotic microorganisms. A remarkable example of this are grassesestablishing symbiotic associations with Epichloë fungal endophytes. We studied thelevel of resistance provided by the grass´ defence hormones, and that provided byEpichloë fungal endophytes, against an introduced herbivore aphid. These fungi protecttheir hosts against herbivores by producing bioactive alkaloids. We hypothesized thateither the presence of fungal endophytes or the induction of the plant salicylic acid (SA)defence pathway would enhance the level of resistance of the grass to the aphid.Methods. Lolium multiflorum plants, with and without the fungal endophyte Epichloëoccultans, were subjected to an exogenous application of SA followed by a challengewith the aphid, Sipha maydis.Results. Our results indicate that neither the presence of E. occultans nor the inductionof the plant´s SA pathway regulate S. maydis populations. However, endophytesymbioticplants may have been more tolerant to the aphid feeding because these plantsproduced more aboveground biomass. We suggest that this insect insensitivity couldbe explained by a combination between the ineffectiveness of the specific alkaloidsproduced by E. occultans in controlling S. maydis aphids and the capacity of thisherbivore to deal with hormone-dependent defences of L. multiflorum.