Abstract
Plants are expected to face novel challenges as consequence of human-driven global change. Outbreaks of pests and higher incidence of contaminants are increasing. Plants can improve tolerance to stress factors through associations with symbiotic microorganisms. Certain grasses establish persistent and asymptomatic symbioses with Epichloe fungal endophytes, which are known to confer protection against Herbivores and improve plant tolerance to abiotic stress factors. Nonetheless, accumulating evidence suggests the symbiosis outcome is context-dependent. We evaluated the capacity of the endophyte fungus E. occultans in protecting the annual grass Lolium multiflorum against a spontaneous larva attack of the generalist herbivore Agrotis ipsilon under episodic exposure of plants to ozone. Symbiotic and non-symbiotic plants were individually grown outdoors and exposed to ozone at different stages resulting in four treatments: control (plant never exposed to ozone), plant exposed to ozone at the vegetative stage, plant exposed to ozone at reproductive stage, and plant exposed to ozone at both stages. After the last exposure, there was an outbreak of A. ipsilon larvae. We evaluated herbivore damage, seed production per plant, and endophyte transmission to the seeds. Frequency of attacked plants was irrespective of both the endophyte and ozone exposure. However, the damage level per plant was only reduced by the endophyte. Seed production was slightly lower in endophyte-symbiotic plants and not affected by ozone. Interestingly, herbivore damaged and undamaged endophyte-symbiotic plants contributed equally to seed production. However, in plants exposed to ozone once at the vegetative or reproductive stage, endophyte-free undamaged plants had higher seed production than endophyte-free damaged plants. Ozone treatments did not affect the transmission efficiency of endophytes to the seeds. Mean endophyte transmission efficiency per plant was 95%. Medium doses of ozone seem to have undetectable effects on grass-endophyte symbiosis, not affecting the defensive mutualism nor the persistence of the symbiont across generations.
Highlights
Worldwide alterations on plant production caused by global change factors is a hot topic in past and current literature, and some impressive changes are predicted to happen over the century (Fuhrer 2003; Thomson et al 2010; IPCC Climate Change 2014)
Symbiotic and non-symbiotic plants were individually grown outdoors and exposed to ozone at different stages resulting in four treatments: control, plant exposed to ozone at vegetative stage, plant exposed to ozone at reproductive stage, and plant exposed to ozone at both stages
Previous research has shown that development of A. ipsilon larvae in perennial ryegrass (Lolium perenne L.) and Schedonorus arundinaceous can be affected by fungal endophytes (Kunkel and Grewal 2003; Baldauf et al 2011)
Summary
Worldwide alterations on plant production caused by global change factors is a hot topic in past and current literature, and some impressive changes are predicted to happen over the century (Fuhrer 2003; Thomson et al 2010; IPCC Climate Change 2014). The use of symbiotic microorganisms as biological control agents for pests and diseases has significantly grown worldwide as an alternative to reduce chemical products in agriculture (Azevedo et al 2000) As part of this group, Epichloë fungal endophytes (family Clavicipitaceae) of grasses are considered a powerful biotechnological tool on the control of diseases, arthropod pests, mammals and birds (Kundau and Bacon 2008; Gundel et al 2013a; Johnson et al 2013; Finch et al 2015; Lugtenberg et al 2016). Epichloë fungal endophytes have been proposed as effective biological control agents as they have been shown to protect host plants against a variety of harmful pests (Kuldau and Bacon 2008) Their success could be limited by natural environmental variability and the increasing incidence of contaminants in the context of climate change (IPCC Climate Change 2014). We assessed the stability of the symbiotic interaction by comparing the relative fitness of endophytesymbiotic vs. endophyte-free plants under experimental enrichment with ozone and herbivory from a spontaneous lepidopteran outbreak, and explored the consequences for symbiosis persistence by checking the endophyte transmission to the generation (see Gundel et al 2008, 2011)
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