Organic agriculture and field edges uphold endospheric wheat microbiota at field and landscape scale.

Agricultural intensification has been demonstrated to induce a loss of biodiversity. Despite the key role of symbiotic microorganisms in plant nutrition and protection, the impact of agricultural intensification on these microorganisms is not fully understood. Organic farming and field edges (as semi-natural elements) may promote a higher microbial diversity thanks to lower anthropic disturbance and higher plant diversity. We sampled wheat individuals in pairs of wheat fields (one organic and one conventional) along a distance gradient to the edges (hedgerow vs. grassy), in 20 landscape windows selected along an uncorrelated gradient of organic farming and hedgerow density. We demonstrated that organic farming shaped microbial composition and increased fungal and bacterial richness, while hedgerows had a neutral or negative effect on richness depending on the microbial phyla considered. In contrast to bacteria, fungal communities were heterogeneously distributed within fields, having a higher diversity for some phyla close to field edges. Overall we highlighted that fungi responded more to the field scale while bacteria were more affected by landscape scale. The effect of agricultural intensification on plant microbiota and therefore on the functions provided by microorganisms to the plants has to be considered at a multiple spatial scale-from field to landscape.

Differentiation of endospheric microbiota in ancient and modern wheat cultivar roots.

Modern plant breeding and agrosystems artificialization could have altered plants' ability to filter and recruit beneficial microorganisms in its microbiota. Thus, compared to modern cultivars, we hypothesized that root-endosphere microbiota in modern wheat cultivars are less resistant to colonization by fungi and bacteria and thus more susceptible to also recruit more pathogens. We used an in-field experimental design including six wheat varieties (three ancient vs. three modern) grown in monoculture and in mixture (three replicates each). Endospheric microbiota of wheat roots were analyzed on four individuals sampled randomly in each plot. Composition-based clustering of sequences was then characterized from amplicon mass-sequencing. We show that the bacterial and fungal microbiota composition in wheat roots differed between ancient and modern wheat cultivar categories. However, the responses observed varied with the group considered. Modern cultivars harbored higher richness of bacterial and fungal pathogens than ancient cultivars. Both cultivar types displayed specific indicator species. A synergistic effect was identified in mixtures of modern cultivars with a higher root endospheric mycobiota richness than expected from a null model. The present study shows the effect of plant breeding on the microbiota associated plant roots. The results call for making a diagnosis of the cultivar's endospheric-microbiota composition. These new results also suggest the importance of a holobiont-vision while considering plant selection in crops and call for better integration of symbiosis in the development of next-generation agricultural practices.

Oviposition Preference of the Cabbage Root Fly towards Some Chinese Cabbage Cultivars: A Search for Future Trap Crop Candidates.

The development of integrated pest management strategies becomes more and more pressing in view of potential harmful effects of synthetic pesticides on the environment and human health. A promising alternative strategy against Delia radicum is the use of trap crops. Chinese cabbage (Brassica rapa subsp. pekinensis and subsp. chinensis) is a highly sensitive Brassicaceae species previously identified as a good candidate to attract the cabbage root fly away from other crops. Here, we carried out multi-choice experiments both in the laboratory and in field conditions to measure the oviposition susceptibilities of different subspecies and cultivars of Chinese cabbages as compared to a broccoli reference. We found large differences among subspecies and cultivars of the Chinese cabbage, which received three to eleven times more eggs than the broccoli reference in field conditions. In laboratory conditions, the chinensis subspecies did not receive more eggs than the broccoli reference. We conclude that D. radicum largely prefers to lay eggs on the pekinensis subspecies of Chinese cabbage compared to the chinensis subspecies or broccoli. Some pekinensis cultivars, which received over ten times more eggs than broccoli in the field, appear especially promising candidates to further develop trap crop strategies against the cabbage root fly.