Fitness alignment of host plant and its vertically transmitted endophyte along a water availability gradient

GARCÍA PARISI, PABLO ADRIÁN; GARELLO, FABIAN ALBERTO; OMACINI, MARINA; MANZUR, MILENA E.

Lyon

Congreso; The 10th congress of the ISS/Holobiont 3 meeting; 2022

Vertically-transmitted, obligated, microbial symbionts of plants should be able to providemultiple benets in several environmental contexts since their own persistence depends onhost plant tness. Thus, some level of environmental limitation, enabling the expressionof one of these benets, is required for increasing mutualistic eectiveness (i.e. the dier-ence on tness between symbiotic and non-symbiotic plants). For example, epichloid asexualendophytes form symbiosis with cool-season grasses and depend on host plant seeds to betransmitted to the next generation. Besides been considered herbivory-protector symbionts,these endophytes can provide several benets to their hosts, including drought tolerance.Our aim is to study mutualisms eectiveness and endophyte transmission eciency alonga water-availability gradient. We developed a greenhouse experiment in pots where plantsof the annual grass Lolium multiforum grew associated (P+) or not associated (P-) withthe endophyte Epichloe occultans. Pots were maintained at ve levels of hydric situationduring the reproductive stage: eld capacity (FC), 63% FC, 40% FC, 25% FC or withoutirrigation during the reproductive stage, until the end of plant cycle. Mutualisms eective-ness was calculated as the dierence on seed production between P+ plants and P- plants.Endophyte transmission eciency was calculated as the percentage of seeds within each P+pot that harbour the symbiont. Mutualism eectiveness was negative at high levels of wateravailability (i.e. P- plants produced more seeds than P+), turning to neutral or positiveas water restriction increases. Instead, endophyte transmission eciency was high and un-aected along water availability gradient. These results indicate that the cost for the hostplant of maintaining the symbiont is compensated in situations of intermediate stress. Thesevertically transmitted symbionts may act as a `constitutive defence´, with the capability toprovide multiple benets against the eventuality of some stress, promoting symbiosis stabilityin fluctuating environments.