Transmission of Leptosphaeria maculans from a cropping season to the following one

Abstract

Current modelling of inoculum transmission from a cropping season to the following one relies on the extrapolation of kernels estimated on data at short distances from punctual sources, because data collected at larger distances are scarce. We estimated the dispersal kernel of Leptosphaeria maculans ascospores from stubble left after harvest in the summer previous to newly sown oilseed rape fields, using phoma stem canker autumn disease severity. We built a dispersal model to analyse the data. Source strengths are described in the spatial domain covered by source fields by a log-Gaussian spatial process. Infection potentials in the following season are described in the space consisting of the target fields, by a convolution of sources and a power-exponential dispersal kernel. Data were collected on farmers' fields considered as sources in 2009 and 2011 (72 and 39 observation points) and as targets in 2010 and 2012 (172 and 200 points). We applied the Bayesian approach for model selection and parameter estimation. We obtained fat tail kernels for both data sets. This estimation is the first from data acquired over distances of 0 to 1000 m, using several non-punctual inoculum sources. It opens the prospect of refining the existing simulators, or developing disease risk maps.

Automated image processing framework for analysis of the density of fruiting bodies of Leptosphaeria maculans on oilseed rape stems

“…From an epidemiological point of view, the space-time partitioning of host crops and pathogen transmission among the cultivated areas and between cropping seasons are main determinants of both invasion and persistence of plant diseases (Hamelin et al, 2011;Bousset & Ch evre, 2013). Within these determinants, the betweenyear (or between-cropping season) transmission of the pathogen, which gives the level of primary inoculum at the beginning of the next cropping season, remains particularly difficult to predict and estimate (Bailey et al, 2004;Bousset et al, 2015). However, this temporal dispersal of the pathogen is an important step in designing and predicting the level of success of mitigation strategies, either based on the use of resistant varieties (Marcroft et al, 2004a), biocontrol agents (Bailey et al, 2004), or preventive management of crop residues (Wherrett et al, 2003).…”

“…Pseudothecia can only be formed following sexual reproduction if isolates of opposite mating types co-occur in the same oilseed rape stem. Spores produced are conidia (pycnidiospores), which are passively rain splashed over short distances, and ascospores, which are actively ejected and wind dispersed (Marcroft et al, 2004b;Savage et al, 2013;Bousset et al, 2015). Infected stubble ensures the carry-over of the fungus from one cropping season to the next (Marcroft et al, 2004a(Marcroft et al, ,2004bLô-Pelzer et al, 2009;Bousset et al, 2018), and serves as the main source of inoculum.…”

The full life cycle of Leptosphaeria maculans completed on inoculated oilseed rape incubated under controlled conditions

“…Pseudothecia can only be formed by sexual reproduction if isolates of opposite mating types co-occur in the same oilseed rape stem. Spores produced in asexual pycnidia and pseudothecia are, respectively, conidia (pycnidiospores) passively rain splashed short distances, and ascospores actively ejected and wind dispersed (Marcroft et al, 2004;Savage et al, 2013;Bousset et al, 2015). The dispersal kernel of L. maculans ascospores from stubble left after harvest in the summer prior to newly sown oilseed rape fields was estimated using phoma stem canker autumn disease severity (Bousset et al, 2015).…”

“…Spores produced in asexual pycnidia and pseudothecia are, respectively, conidia (pycnidiospores) passively rain splashed short distances, and ascospores actively ejected and wind dispersed (Marcroft et al, 2004;Savage et al, 2013;Bousset et al, 2015). The dispersal kernel of L. maculans ascospores from stubble left after harvest in the summer prior to newly sown oilseed rape fields was estimated using phoma stem canker autumn disease severity (Bousset et al, 2015). Infected stubble ensures the carry-over of the fungus from one season to the next (Marcroft et al, 2004;Lô-Pelzer et al, 2009;L.…”

A Spatio‐Temporal Exposure‐Hazard Model for Assessing Biological Risk and Impact

“…Crops are damaged by pests and diseases, whose spatio‐temporal dynamics are complex and driven by landscape patterns, cropping systems, and agricultural practices, including the possible use of pesticides. Diseases are maintained over cropping seasons through reproduction and survival processes and may disperse between fields as exemplified by the phoma stem canker, a major disease of oilseed rape caused by the fungus Leptosphaeria maculans and spread via wind‐borne spores . In this case, oilseed rape fields infected during the first season are sources of pathogen, oilseed rape fields grown on the second season are the exposed population (oilseed rape is usually not grown in the same field on consecutive years because of unreasonable risk of contamination).…”