Transgenerational effects of tropospheric ozone on the resistance to aphids in Lolium multiflorum in interaction with the fungal endophyte Epichloë occultans

CROCCO C; GUNDEL, P.E.; UENO A; MA MARTINEZ-GHERSA; BUBICA BUSTOS L

Salamanca

Congreso; 10th International Symposium on fungal endophytes of grasses; 2018

Universidad de Salamanca

Plants are simultaneously challenged by biotic and abiotic stress factors in nature. The order in which factors affect plants is important, as the first one can induce the plant resistance or susceptibility to the next one. An increasing number of studies is showing that this sequential effect of stress factors can have effects for more than one generation. For instance, the attack of plants by herbivores can improve the defense response of the progeny, suggesting the existence of transgenerational mechanisms that can optimize the ecological fitness of the progeny [1]. The symbiosis of plants with vertically transmitted microorganisms could be an additional mechanism to transmit information between plant generations and this could be the case of fungal endophytes of grasses [2]. Ozone gas is a tropospheric contaminant [3] that causes oxidative stress in plants damaging their structure and function but, in some cases, it can also promote the activation of defense systems and increase the accumulation of phenolic compounds [4,5]. It is known that ozone affects negatively the resistance to aphids against aphids conferred by fungal endophytes [6], but it is uncertain whether this effect persists in the following generation. Here, we studied the transgenerational effect of ozone on the resistance to aphids in grasses symbiotic with vertically-transmitted fungal endophytes. We exposed L. multiflorum plants with (E+) and without (E-) Epichloë occultans to two levels of ground ozone [(120ppb) and (0ppb)]. One year later, we evaluated the resistance level of the progeny coming from all four combinations (endophyte by ozone) to the aphid Rhopalosiphum padi. The resistance level was characterized through the aphid´s population size and the total level of phenolic compounds, and plant performance through the aboveground biomass. The resistance to aphids conferred by endophytes was negatively affected by the ozone applied to mother plants (POzonexEndophyte=0.023). In addition, the ozone boosted the resistance level of non-symbiotic plants. The endophyte effect on the concentration of total phenolic compounds depended marginally on the exposure of mother plants to the ozone (POzonexEndophyte=0.093). The aboveground biomass was 15% higher in E+ than in E- plants irrespective of the effect of maternal ozone (PEndophyte=0.001). Our results show that ozone induced transgenerational resistance in E- plants but it was not associated to an increased level of phenolic compounds. On the other hand, the maternal ozone reduced the progeny?s resistance level against aphids in E+ plants, which could be connected with oxidative stress caused by the ozone [7] on fungus endophyte performance.