Difference between revisions of "Team:Bordeaux/Problem"

The Problem: Downy mildew

In 2015, vineyards are still threatened by the disease

Downy mildew is a disease caused by an oomycete (fungus-like eukaryotic microorganism) called Plasmopara viticola . It is unfortunately famous in the Aquitaine region because it affects tens of hectares of Bordeaux vineyards every year and threatens wine production . Until the middle of the 20th century, research efforts were mainly concentrated on optimizing the application of cooper fungicides such as "Bouillie Bordelaise" and developing new molecules for controlling the disease. Now, more and more alternative treatments are being tested and effective models which take into account meteorologic conditions are being developed. This could drastically change the environmental impact of winemaking.

Our iGEM team has been following this year's effect of mildew closely reading the official vineyard mildew bulletins available on the vinopole website. In the past few months ( June 2015 ) there has been another violent attack of mildew on the grapevines in the Aquitaine region. Up to 60% of wine grapes have been infected on certain parcels [4] and the vice president of the agriculture chamber, Patrick Vasseur, hasn't been underestimating the economic significance this could have since the wine production will evidently be affected. He calls the situation "exceptional" since "even the main branches are affected"

Serge Audubert, head of 3 castles in the region and owning a total of 24 ha, has been watching the effects on his land. On his 17 ha of château-laborde grapevines, in Saint-Médard-de-Guizières, 2ha are severly touched. « the leaves, the branches, the grapes, everything is affected. We are going to lose at least 50% of the grapes on these 2 ha. » On the first of May, this vineyard observed a spot on a branch, nothing severe especially since the « Bulletin de santé du végétal » (plant health review) which came out a few days before clearly states that the conditions aren't favorable for contaminations. As a precaution, Serge Audubert starts his preventive treatments on the 7th of May. On the 15th of May, the outburst starts, shocking the entire region: « I have been living here since 1987. I have never seen something like this. Informatics models were supposed to alert us when mildew evolution becomes dangerous. » Without better models and solutions to prevent mildew infections, winemakers in the region remain threatened every year!

Common Solutions

Since repairing damaged tissues infected by downy mildew is impossible, the majority of the solutions available to vineyards are preventive solutions, mainly through preventing primary infections. This is done by spraying fungicides on the organs that are most infected: leaves and stems. The most efficient preventive treatment was discovered at the end of the 19th century: a solution made of copper sulfate also known as "Bouillie Bordelaise", the only treatment used until the end of the 20th century.

Recently, more models and devices designed to be used by individual growers measure temperature, humidity and leaf wetness and provide treatment recommendations based on algorithms similar to the Goidànich model. This general algorithm defined as the 3–10 spray strategy, is prescribed when the average temperature is above 10°C, more than 10 mm of rain have fallen within 24 h and shoot length in the vineyard is at least 10 cm. Despite evident imprecision due to the strict parameters, this general model can reliably predict the first risk period and recommend thereafter a treatment schedule that will allow growers to prevent development of severe downy mildew in vineyards.

The weakness of this type of model is that the number of recommended pesticide sprays is usually greater than what is needed to avoid an epidemic, particularly at the beginning of the season. In 2006, Swiss researchers applied a concept based on a tolerance threshold for Downy mildew under the particular climatic conditions of southern Switzerland and were able to eliminate half of the recommended treatments. (Jermini et al., 2006). This paradigm change, from a focus on the pathogen and the disease toward a threshold concept, requires detailed knowledge of the host and its relationship with the environment and human activities but opens the path for a new era of pesticide applications. However, these are highly complex interactions and there is little available data describing them. The information that is available is heavily biased by site, year and cultivar factors, and so cannot be readily used for simulation and modeling activities. [1] More similar studies could help reduce the use of pesticides in the region.

Plant natural defenses

Plant immunization is based on the same principle as human immunization: activating its natural defenses before contamination by an infectious agent. The concept is simple; putting the plant in contact with a molecule able to activate it's natural defenses: an elicitor . In nature, there are many elicitors produced by micro-organisms (exogenous elicitors) or by the plant itself when it is attacked (endogenous elicitors). The presence of an elicitor in the plant triggers a series of cellular reactions including the production of molecules to strengthen the resistance of cell walls , but also the production of plant antibiotics such as phytoalexins or defense proteins. These compounds have antifungal and antibacterial properties. The external application of a natural elicitor or a similar synthetic molecule thus results in the production of phytoalexins or defense proteins in the absence of any pathogen. The "immunized" plant is ready to fight back if attacked.

First, the cell wall forms a physical barrier which prevents the penetration of most microbes. Then, if some pathogens are able to cross this wall, the infection depends on the ability of the plant to perceive and to trigger defense reactions that would prevent the development of the disease. This recognition is done with certain compounds, known as elicitors from the pathogen or plant. The fixing of an elicitor to a plant cell receptor initiates a cascade of events that leads to the synthesis of defense compounds . The best known are antimicrobial compounds such as phytoalexins and Pathogenesis Related proteins .

There are two types of defenses: "passive" and "active". Natural defense reactions of plants are passive when these components were preformed prior to infection. They remain active until the pathogen penetration. Active defenses are induced upon recognition of the pathogen and remain active during infection.

Literature Cited:

[6] Stimulation of plant natural defenses Sciences de la vie.2001 Oct;324(10):953-63

Figure 3: Schematic representation of the plant's imune system