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This multidisciplinary pre-competitive research project aims to understand and quantify, on a farm and territorial scale, the challenges of future climate change for the plant sectors in Brittany and Pays de la Loire. It also aims to study innovative solutions for adapting to and mitigating the impacts of climate change, placing farmers, wine growers and horticulturalists at the heart of the dynamics and strategic thinking.
Beyond the production of knowledge, this project has a role in creating and structuring a solid network for a more resilient and supportive agriculture.
Finally, the project aims at a global and efficient communication towards all the actors of the sector, on all the studied innovations.
STREMHO is participating in the CLIMATVEG project through the action "Priming of mother plants and seedlings to increase resilience to water stress (ornamental and market gardening)", which it is leading. This action is carried out in collaboration with ASTREDHOR (Loire-Bretagne Station) and the horticultural vocational school Angers-Le Fresne, and in relation with the Pépinières EARL Pépinières Goarant and Du Menec.
 The objective will be to validate whether, under horticultural production conditions, the priming of mother plants and rootstocks of horticultural species can contribute to their acclimatisation to water stress as well as to that of their clonal (plants from cuttings) and sexual (plants from seeds) descendants.
In addition to traditional varietal improvement based on genetic mixing, the exploitation of plant plasticity is another strategy that can contribute to their adaptation to environmental stresses. Research has shown that epigenetic regulations are induced by the stresses that plants undergo and that they participate via a process called "priming" or "conditioning" in the acclimatisation of plants to future stresses. These epigenetic regulations can be transmitted through vegetative propagation and sometimes even sexually to the offspring, giving them an acclimatisation similar to the parental line. However, these results have only been reported for a few species, which are often models and studied under experimental conditions.
 The objective will be to verify whether, in horticultural species cultivated under production conditions, conditioning of mother plants or seedlings to environmental stress can make it possible to obtain acclimatised young plants that produce crops that perform better under this stress. Water stress, the major stress suffered by plants in view of the scarcity of water resources and climate change, is the stress studied.
 The degree of acclimatisation of plants to water stress will be measured using phenotypic, physiological and molecular markers. These markers will ultimately contribute to the development of a "Priming" Decision Support Tool that will allow producers to assess the level of conditioning of young plants prepared in this way, and in an underlying manner its level of resistance to water stress.
 Our work will focus on ornamental plants and vegetable plants for the gardening public. The production of horticultural seedlings is one of the jewels in the crown of the Pays de Loire horticultural industry. For example, vegetable seedlings represent 15% of the plant sales of horticultural production companies in the Pays de la Loire Region, worth €50 million (FranceAgriMer & AND International, 20191)[1], a value that has been rising significantly in recent years (+38% since 2015). The species studied in this section are species that are widely grown by consumers (i.e. home gardeners), namely: tomatoes, petunias and hydrangeas.
 Through the choice of horticultural plants for the consumer and in connection with the UMT STRATège (led by ASTREDHOR in partnership with the UMR IRHS, but also Végépolys Valley, INRAE, University of Angers), dedicated to the development of the urban horticultural market, (www.umt-stratege. fr), our work will also contribute to meeting society's demand for more plants in the city by proposing plants that are better adapted to the difficult growing conditions of the urban environment (heat islands and high summer temperatures in the city, agronomically poor soil, limited water resources).
 Vegetable plants for consumers are produced using the same production tools as ornamental plants, and therefore by horticulturists according to specific cultivation itineraries that are different from those used for professional market gardening. This explains the partnership with ASTREDHOR - Institut technique de l'horticulture.

Through its research stations, the Institute has the necessary infrastructure and skills to conduct these experiments. The Breton station of CATE, which specialises in the cultivation and multiplication of woody ornamental plants, will carry out the experiments on hydrangea mother plants.
 Another part of the greenhouse experiments will be carried out by the Lycée horticole d'Angers-Le Fresne. This high school trains students in horticulture with practical situations. Experiments will be carried out with the students under the supervision of a teacher to contribute to their training in innovative cultivation approaches. The school has a set of tools adapted to the conduct of experiments under water stress.

The physiological, biochemical and molecular analyses that will contribute to the development of the "Priming" DAO will be conducted at the IRHS (Institut de Recherche en Horticulture et Semences), in particular by the STREMHO (Stress, Epigenetics and Memory of Horticultural Plants) team, which has the necessary skills to identify the markers required to develop the DAO. This team is made up of ecophysiologists who have been studying the impact of environmental factors on the development of horticultural plants for many years (Demotes et al. 2013; Leduc et al. 2014; Rameau et al. 2015; Huché-Thélier et al. 2016, Roman et al., 2016, Corot et al. 2017, Porcher et al, 2020). It works in close collaboration with the horticultural profession. Since 2017, the team has been interested in the mechanisms of priming, acclimatisation and memory of plants to stresses, in particular water stress. Finally, it hosts the managers of the UMT STRATège (supported by ASTREDHOR) and studies with them the levers for the development of urban horticulture.
 The choice of varieties studied and the results of our work will be discussed with horticulturists, in particular the Ferme de Ste Marthe (production of market garden seeds from organic farming) and two hydrangea producers, members of the Kérisnel cooperative (EARL Pépinières Goarant and EARL Pépinières du Menec)

References

Corot A, Roman H, Douillet O, Autret H, Perez-Garcia MD, Citerne S, Bertheloot J, Sakr S, Leduc N and Demotes-Mainard S. 2017 Cytokinins and Abscisic Acid Act Antagonistically in the Regulation of the Bud Outgrowth Pattern by Light Intensity. Frontiers in Plant Science 8,1724

Demotes-Mainard S., Huché-Thélier L., Morel P., Boumaza R., Guérin V., Sakr S. 2013. Temporary water restriction or light intensity limitation promotes branching in rose bush. Scientia Horticulturae, 150: 432-440.

Huché-Thélier L., Crespel L., Le Gourrierec J., Morel P, Sakr S., Leduc N. 2016. Light signaling and plant responses to blue light and UV radiation - Perspectives for applications in horticulture. Environ. Exp. Bot., 121: 22-38.

Leduc N, Roman H, Barbier F, Peron T, Huché-Thelier L, Lothier J, Demotes-Mainard S, Sakr S. 2014. Light signaling in bud out growth and branching in plants. Plants, 3: 223-250

Porcher A, Guérin V, Montrichard F, Lebrec A, Lothier J, Vian A (2020) Ascorbate glutathione-dependent H2O2 scavenging is an important process in axillary bud outgrowth in rosebush. Annals of Botany (in press).

Rameau C, Bertheloot J, Leduc N, Andrieu B, Foucher F, Sakr S. 2015 Multiple pathways regulate shoot branching. Frontiers in Plant Sciences 5: 1-15. doi: 10.3389/fpls.2014.00741.

Roman H, Girault T, Barbier F, Péron T, Brouard N, Pencík A, Novák O, Vian A, Sakr S, Lothier J, Le Gourrierec J, and Leduc N (2016) Cytokinins Are Initial Targets of Light in the Control of Bud Outgrowth. Plant Physiol 172: 489-509

[1](FranceAgriMer & AND International, 2019) "Observatoire des données structurelles des entreprises de production de l’horticulture et de la pépinière ornementale – Pays de la Loire" (Données 2018 - Synthèse 2019).