Quantification of sporangia and zoospore production in a plant pathogen oomycete using an automatic particle analyser
Résumé
Crop pathogens have to adapt to a broad range of selective pressures such as varying cultural practices, climate change or new host genotypes [1,2]. Studying pathogen trait evolution to understand and predict the response of pathogen populations to new selective pressures is an urgent need for an accurate management of crop production. Most commonly measured traits in plant-pathogen systems include infection efficiency, latent period, spore production rate, infectious period and lesion size [3,4]. In oomycetes (that cover most of the phytopathogenic species along with fungi), spore production rate estimates focused on sporangial production. However, most oomycete sporangia produce zoospores, that are rarely quantified despite the acknowledged importance of this unit of infection. In this study, we describe a quick-and-easy method to simultaneously quantity sporangia and zoospore production in Plasmopara viticola, the causal agent of grapevine downy mildew. We successfully used an automatic particle analyzer to count and size the sporangia and zoospores produced in 43 P. viticola isolates collected in French vineyards. We analyzed the sporulation of these isolates inoculated on the susceptible V. vinifera cv. Cabernet Sauvignon in a leaf-bioassay and compared the number and size of particles (sporangia and/or zoospores) produced at t = 0 min (no zoospore release) and t = 100 min (zoospore release). Using an automatic particle analyzer, we highlighted two well separated peaks for sporangia and zoospore particle number in two different size ranges. Each sporangia produced a mean of 5.8 ± 2.3 (SD) zoospores. This procedure allows a valid quantification of zoospore production rate in oomycetes and make it possible to study the infection potential of plant pathogens in various agro-ecological contexts. References: [1] Anderson, P. K., Cunningham, A. A., Patel, N. G., Morales, F. J., Epstein, P. R., & Daszak, P. (2004). Emerging infectious diseases of plants: pathogen pollution, climate change and agrotechnology drivers. Trends in Ecology & Evolution, 19(10), 535-544. [2] Burdon, J. J., & Thrall, P. H. (2008). Pathogen evolution across the agro-ecological interface: implications for disease management. Evolutionary Applications, 1(1), 57-65. [3] Pariaud, B., Ravigné, V., Halkett, F., Goyeau, H., Carlier, J., & Lannou, C. (2009). Aggressiveness and its rolein the adaptation of plant pathogens. Plant Pathology, 58(3), 409-424. [4] Lannou, C. (2012). Variation and selection of quantitative traits in plant pathogens. Annual review of Phytopathology, 50, 319-338.