Indicators & Prophylaxis

BEYOND will have an impact on plant health management by creating more opportunities to avoid the use of synthetic pesticides and to replace them with agronomic practices.  These impacts will be pertinent, in the short term, to the pathosystems that we will directly study in BEYOND: 15 pathosystems representing a range of mostly horticultural crops and a range of pathogens that are disseminated by wind, water, insect vectors and/or exchange of plant materials or that reside in the soil (see the lists below). For about half of these pathosystems, ample epidemiological data are available so that the added benefit of new indicators for surveillance can be assessed before we attempt to adapt them to additional pathosystems. By communicating about the innovations that could and do eventually arise from BEYOND to the research community and to other stakeholders, we intend for the impact on French agriculture to be extended to plant production systems in Europe and worldwide where they are pertinent.

At the start of the project we can already speculate on the new types of indicators that we will develop in this project that will have an impact on prophylaxis.

1. In BEYOND we will develop indicators to anticipate the long-distance arrival of plant pathogens and pathogen-carrying insects via the atmosphere. This will allow for surveillance upstream of target crops and will give time for preemptive protection of crops with biological control, or the use of physical barriers, for example. This could also be an important strategy to slow the dissemination of certain quarantine pathogens. This will be explored for diseases disseminated by wind and/or insects:

• Brown rot of peach (Monilinia fructicola, Monilinia fructigena, Monilinia laxa)
• Powdery mildew of tomato (Oïdium neolycopersici)
• Sharka of Prunus  spp. (Plum pox virus vectored by aphids)
• Yellows and mosaics of cucurbits (virus [CMV, WMV, CABYV, ZYMV] vectored by aphids and whiteflies)
• Huanglongbing (HLB) of Citrus  spp. (‘Candidatus Liberibacter spp.’ vectored by psyllids)
• Zebra chip of potato (‘Candidatus Liberibacter solanacearum’ vectored by psyllids, viz. Bactericera cockerelli)
• European stone fruit yellows (ESFY) of Prunus  spp. (‘Candidatus Phytoplasma prunorum’ vectored by psyllids)

2. Surveillance of pathogens can be hampered by insufficient knowledge of the full scope of reservoirs of pathogens both within and outside of agriculture. In BEYOND, we will confront this constraint to surveillance by expanding knowledge of reservoirs. Then we will explore how information from surveillance of reservoirs beyond the crop and its immediate context can influence decisions about management of plant health for diseases for which inoculum reservoirs are suspected to be well beyond what is currently known or accounted for in surveillance:

• Powdery mildew of tomato (Oïdium neolycopersici)
• Bacterial cankers of kiwi and apricot (Pseudomonas syringae)

3. Aerial movement of pathogen propagules in a cropped field is already used to judiciously deploy phytosanitary treatments. In BEYOND we will enhance the utility of this approach by optimizing the positioning of air samplers and by boosting risk indicators with information about climatic conditions for diseases where surveillance of air-borne spores is already a standard practice:

• Mildews and Black rot of grapevine (Plasmopara viticola, Erysiphe necator, Guignardia bidwellii)

4. We will also develop indicators that summarize the geographical, land use and pedoclimatic contexts of crop production linked to the receptivity of crops to pathogen propagules and to disease symptoms. From these indicators we will establish risk maps for present cropping zones and for predicting future risks based on anticipated climate and land use change. In the long term, these predictions could be deployed to adapt land use accordingly. This will be explored for

• Bacterial cankers of kiwi and apricot (Pseudomonas syringae)
• Leaf scorch of olive and a range of other perennial plants (Xylella fastidiosa vectored by various sap-sucking insects)
• Fusarium wilt of banana (Fusarium oxysporum fsp. cubense)
• Brown rot of garlic (Fusarium proliferatum)
• Vector-borne bacterial diseases in general (phytoplasmas and Liberibacter)

5. The risk maps that we will develop from a wide spectrum of environmental indicators (indicated in #4) can also be coupled to additional indicators of the genetic variability of the pathogen and to behavioral tendencies of farmers relative to their agronomic practices. The added value of such multidimensional indicators in the deployment of prophylaxis will be explored for:

• Flavescence dorée (FD) of grapevine (FD phytoplasmas vectored by leafhoppers)

6. Trade flow of plant materials via commerce is also a very important means of disseminating disease and of introducing pathogens and their vectors into new regions. By mapping networks of movement of plant materials, a warning system could be established that could be especially useful when disease emerges in nursery stock.  This approach will be explored for:

• Brown rugose, mosaics and yellow of tomato, pepper, cucurbits (various viruses, including ToBRFV, disseminated by commercial exchange of plant material)
• Sharka of Prunus spp. (Plum pox virus vectored by aphids)