Seeds are key components of plant fitness and are central to the sustainability of the agri-food system. Both the seed quality for food consumption and the seed vigor in agricultural settings can be influenced by the seed microbiota.

Plant resistance inducers, also called elicitors, could be useful to reduce the use of pesticides. However, their performance in controlling diseases in the field remains unsatisfactory due to lack of specific knowledge of how they can integrate crop protection practices. In this work, we focused on apple crop and acibenzolar-S-methyl (ASM), a well-known SAR (systemic acquired resistance) inducer of numerous plant species. We provide a protocol for orchard-effective control of apple scab due to the ascomycete fungus Venturia inaequalis, by applying ASM in combination with a light integrated pest management program. Besides we pave the way for future optimization levers by demonstrating in controlled conditions (i) the high influence of apple genotypes, (ii) the ability of ASM to prime defenses in newly formed leaves, (iii) the positive effect of repeated elicitor applications, (iv) the additive effect of a thinning fruit agent.

Gloria torres-cortes 2,4* the assembly of the seed microbiota involves some early microbial seed colonizers that are transmitted from the maternal plant through the vascular system, while other microbes enter through the stigma. Thus, the seed microbiota consists of microbes not only recruited from the plant vascular tissues, but also from the flower. Flowers are known to be a hub for microbial transmission between plants and insects. This floral-insect exchange opens the possibility for insect-transmitted bacteria to colonize the ovule and, subsequently, the seed to pass then into the next plant generation. In this study, we evaluated the contribution of insect pollination to the seed microbiota through high-throughput sequencing. Oilseed rape (OSR) flowers were exposed to visits and pollination by honey bees (Apis mellifera), red mason bees (Osmia bicornis), hand pollinated or left for autonomous self-pollination (ASP). Sequence analyses revealed that honey bee visitation reduced bacterial richness and diversity in seeds, but increased the variability of seed microbial structure, and introduced bee-associated taxa. In contrast, mason bee pollination had minor effects on the seed microbiota. Our study provides the first evidence that insect pollination is an ecological process involved in the transmission of bacteria from flowers to seeds. In nature, plants live in close association with a diversity of micro-and macro-organisms, both within and outside their tissues. Microbes may play beneficial roles in plant growth and development, positively affecting plant biomass or disease resistance 1-3. Although numerous studies have focused on microbial assemblages associated with different plant organs 4,5 , little is known about tripartite interactions between plants, their microbiomes and other multicellular organisms, such as pollinators. Insect visitors acquire and deposit microorganisms onto flower surfaces during nectar and pollen collection 6-9 , thus shape the flower microbiota 10-12. These flower-associated microbes are mainly fungi, followed by bacteria 10. A recent study has shown that these flower inhabitants can act as intermediaries of plant-pollinator communication; bees innately avoid flowers inhabited by bacteria but are not deterred by yeasts 13. Moreover, microorganisms transported by insects may influence plant-pollinator interactions; this is the case of yeasts transported by ants that change nectar composition 8. Furthermore, since the flower microbiota serves as one of several inocula for the plant ovule and, hence, for the seed 14 , it is possible that by affecting the microbial community of the flower (including pollen), pollinators could modify the seed microbiota. The role of insect vectors in the dispersal of bacteria and fungi to roots, stems, leaves, flowers, and fruits is well documented 15,16 , while their role in the microbial assembly of the seed has yet to be described. During seed-to-seed development, some early microbial seed colonizers are transmitted from the mother plant to the o...