Biology subjects

Gregoire, J.-C.

Publications and source records attributed to Gregoire, J.-C..

3 recordsLinked to original sources

bioRxiv2022

Measuring the threat from a distance: insight into the complexity and perspectives for implementing sentinel plantation to test host range of Xylella fastidiosa

The sentinel plantation concept consists of assessing the impact of exotic factors, such as pests and pathogens, on plants of interest by planting them out of their native range. This tool is a way to enhance knowledge for pest risk analysis (PRA) by guiding decisions on how quarantine organisms should be regulated and where to focus prevention and surveillance efforts for an early detection. In this study, the sentinel method was used in the case of research on Xylella fastidiosa, a plant pathogenic bacterium that has recently been found established in southern Europe, but whose potential impact and possible host range are still poorly documented in northern areas where the bacterium is not known to occur. To improve knowledge on the susceptibility of potential hosts of X. fastidiosa in northern Europe, a sentinel plantation of Prunus domestica cv. Opal, Quercus petraea and Salix alba was established in the X. fastidiosa-infected area of Majorca. In order to assess the circulation of the bacterium in the sentinel plot and around it, surveys of the local flora and insect vectors were carried out, as well as the planting of a network of rosemary "spy plants". Symptomatic monitoring and molecular analyses were performed on the sentinel plants for four years. During these years, X. fastidiosa was never detected in our sentinel plants most likely because of the low infectivity pressure recorded in the surroundings. This study underlines the complexity of conducting sentinel plantation assays combined with X. fastidiosa research, highlighting the need for long-term investigation and questioning the efficiency of the sentinel tool. However, this study is placed in perspective with other valuable sentinel plantations. It also highlights the complementarity of the tool and proposes elements to improve or reorient the implementation of future sentinel projects.

ecology↗

bioRxiv2022

Salicaceae as potential host plants of Xylella fastidiosa in European temperate regions

The discovery of three subspecies of Xylella fastidiosa in Europe has triggered major attention on the potential spread up North of the bacteria. Assessing the susceptibility of a previously unexposed European flora is a key element that remains widely unknown. Under biosafety facility, we evaluated the susceptibility of Salicaceae such as Populus tremula, Populus canescens, Salix alba and Salix caprea by mechanically inoculating the KLN59.3 GFP-labelled X. fastidiosa at 22 {degrees}C and at 28 {degrees}C. Bacterial movement and multiplication in plants were investigated by PCR, real-time PCR, confocal or scanning electron microscopy. Nine months post-inoculation, 100 % of the plants tested positive for X. fastidiosa, with the exception of 57% for P. canescens under the 22 {degrees}C-growing conditions. Bacteria were detected up to 120 cm from the inoculation point for S. alba. They were detected in the roots of all species and were successfully isolated for S. alba and P. tremula. Estimates of average CFU/g of plant tissue per species ranged from 1.5E + 03 to 3.5E + 06, with the lowest figures for P. canescens and the highest for P. tremula together with high number of totally obstructed vessels observed by confocal microscopy. The possibility of insect transmission was also evaluated using an experimental set up based on Mallorca Island. There, transmission by P. spumarius of both X. fastidiosa ST1 and ST81 was proven on S. alba. We thus demonstrated that indigenous European Salicaceae such as S. alba or P. tremula are new potential hosts for X. fastidiosa.

plant biology↗

bioRxiv2022

Cosmopolitan Scolytinae: strong common drivers but too many singularities for accurate prediction

AimMany scolytine beetle species have been expanding their range in new territories across geographic barriers, traveling with wood, wood products and plants for planting, sometimes with a high impact on plant health. Here we attempt to quantify the mobility of these cosmopolitan species and to identify the biological drivers of mobility and impact. LocationWorld Major taxa studiedColeoptera; Curculionidae; Scolytinae MethodsMobility was estimated by counting the numbers of landmasses (contiguous pieces of land, surrounded by ocean or sea) colonized by each species. A series of potential drivers (taxonomic tribes; feeding habits; polyphagy; reproductive strategy; host taxa; pheromones and primary attractants) as well as impact on host health were recorded. Results163 species were identified, out of 5546 counted in the whole subfamily. Four tribes (Xyleborini; Ipini; Crypturgini; Hylastini) were significantly over-represented, and two others (Corthylini; Hexacolini) were under-represented. 53% of the 163 species are inbreeding, a very significant excess as compared to the whole subfamily (29%). The inbreeders colonized more landmasses than the outbreeders. There is a significant relationship between the number of host families attacked by a species and the number of colonized landmasses. Species restricted to conifers colonized fewer landmasses than hardwood generalists. Species attacking both types of hosts are the most mobile. Most of the invasive species respond to host primary attractants, only one quarter respond to pheromones. All very mobile species respond to primary attractants, and none responds to pheromones. Very mobile species are all associated with a high or moderate impact. Main conclusionsThe most mobile species belong for a large part to a limited number of subtribes. They are often inbreeding, polyphagous and respond to primary attractants but do not produce pheromones. However, many species that do not, or only partly, belong to these categories, have established in several landmasses, sometimes with a high impact. For example, the outbreeding Scolytus multistriatus, that attacks only 3 host families and produces aggregation pheromones, has established in thirteen landmasses, with a high impact. Therefore, risk prediction needs to assess diversity of species-specific biological traits beyond the few routinely analyzed in literature.

ecology↗