The fungus Botrytis cinerea called Botrytis Leaf Blight, or Grey Mould in English is very common in the whole world. As it attacks a lot of different hosts, it can have an important impact on economics of an activity and a production. For example, it seriously attacks chickpeas in India, or even our Christmas trees in France. In fact, the biggest problem in France is the attack of vineyards. As it is one of the most famous activities in France, the problem of this fungus must be avoided and fought.
II Susceptible species
This fungus has a very large host scale. In fact, it attacks trees and especially conifers like Western hemlock Tsuga heterophylla, Norway spruce Picea abies, Douglas fir Pseudotsuga menziesii and even Western Red Cedar Thuja plicata. Moreover, a lot of ornamental species are attacked : flowers like begonia, dahlia, geranium or tulips are very weak and commonly damaged by this disease. Finally, the main species that is susceptible to be infested is vine Vitis vinifera, which represents a great activity of production of wine in France.
But all these names are only examples, as apples, tomatoes, peppers or onions are attacked by this species of fungus. So, the list is too long to be detailed here, as 235 species can be affected by it.
This fungus is common in forests and even in nurseries. So, there is no specific distribution in France as it can be everywhere. However, it is more present in the Mediterranean zone, and attacks production of tomatoes for example. Concerning forests, Douglas fir is mainly attacked in Bourgogne, almost in the centre of France. It is also a great region for production of wines, so, this fungus is present there. It also attacks Spruce, which was mainly introduced in France. Besides, as it is also natural in mountains, the weather conditions here favour the development of the disease.
This disease was first discovered by Micheli. However, it had another name, and was called Botryotinia fuckeliana. Its biological origin is fungal, which means that it is a biotic origin. A fungus belongs to the fifth kingdom : so, it is neither an animal, nor a vegetal. It is a saprophyte and heterotrophic organism, so, it uses dead organic matter, as it cannot produce its own matter.
This pathogen is a fungus belonging to Ascomycota. It development is asexual. Moreover, it is developed by a spore which grows under specific climatic conditions. This seed permits to wait for ideal conditions of growth. After cellular divisions of this spore, we obtain a mycelium which can survive during a few years. When conditions are favourable, the mycelium can grow and extend the area of fungus, and the quantity of inoculum. The mycelium creates some sclerotia, which are resistant enough to make the fungus survive during the winter. Furthermore, some conidiophores and conidies are created as reproduction cells.
The primary infection is always on weak parts of a plant (parts weakened by frost, or wounds...). After that, the fungus can develop in healthy parts, especially succulent ones. This pathogen is said necrotroph. Therefore infested soils and crumbs of vegetable matter are a really good source of inoculum.
With this mycelium which survives to extreme conditions, spores that are produced, are scattered to conquer other plants. The main factors of dissemination are Wind and Rain. Furthermore, some conditions are favourable to the spread : air moisture and low temperature. Indeed, air moisture of almost 90% and 15-20°C of temperature are described to be good figures for the spread of this disease.
This disease provokes appearance of some black stains on leaves. With time, necroses appear. Besides, some grey mould can be visible on the surface of leaves. It is the origin of fading of leaves, which rot and fall after a certain time. It can also affect shoots and buds. It means that, if there is a fading of these parts, growth will be rather compromised.
Concerning the vine, it affects leaves and even fruits which rot and become often unfit for consumption. However, some wines are made with infested fruits. Thus the quality can be better for these wines, and that is why one of the nicknames of the fungus is Noble blight, in certain cases.
If the disease is not present, we can prevent it from arriving in our crops and plantations. In fact, this control consists in checking the density of plantations, cutting branches to limit the foliage area, removing the dead or rotten leaves and other crumbs that could be infested... As we know the conditions that favour the appearance and development of the disease, we can find some treatments to prevent it from happening.
However, once the disease infests a crop, some solutions exist to stop or limit it. In fact, we have to isolate infested trees from non-infested ones, remove the infested parts of a tree, and improve the circulation of air and sun light... Besides, moisture is really an important thing to control. Thus, if some seedlings must be sprayed with water, it should be done in the morning, to let leaves dry fast with the sun.
Moreover, we do not use a lot of fungicides, as it could be the best way for the fungus to develop a resistance against it. So, their use is really limited.
IX Research fronts
The infection is well-known as a lot of studies were led to discover the impact of environmental factors on it. However, some parts of this disease are quite unknown for the moment and need to be developed. For example, “The role of inoculum sources in Botrytis cinerea epidemics in the vineyard system.” is a topic led in New-Zealand : Alison Seyb has “to identify inoculum sources and develop a model to describe the environmental conditions leading to infection from various sources in the vineyard.”
Besides, our knowledge concerning origin of spores and dissemination of them are limited. But resistance of the fungus is also one of the topics that interests scientists, as well as development of a biological agent to fight the fungus (e.g. Microdochium dimerum)
• PRADESH Andhra, Integrated management of Botrytis grey mould of chickpea, International Crops Research Institute for the Semi-Arid Tropics, Information Bulletin n°61, 32 pp.
• BONNEAU G., INNES L., LACHANCE C., MARCHAND L., PARE D., Maladies et insectes importants dans les pépinières forestières, au Québec. Direction de la conservation des forêts, January 1997, pp.19-20.
• Tree Doctor Software, developed by CFPF, French Agriculture and fishing Minister, Chlorophyl Assistance, Citare, French forest development Institute, Disease and advisory Service forest research, Instituto per le piante de legno e l’ambiente, Alterra, Staatsbosehner, IPC groene ruimte