Fertilisers against plant diseases

Press release of September 6, 2011

Certain substances that induce the resistance of strawberry plants against grey mould (Botrytis cinerea) can be more efficient depending on the level of nitrogen fertilisation. This is one of the findings of Philippe Nicot, a researcher at the INRA (National French Institute for Agricultural research) who will present his findings within the framework of the congress PR-IR11 in Neuchatel.
It is well known that nitrogen fertilisation have an effect on the susceptibility of plants to certain pests and diseases. However, little is known on the interactions between these fertilisers and biological control agents, particularly with respect to products that stimulate natural defences in plants. Hence, the studies carried out by Philippe Nicot, a researcher in the Plant Pathology Research Unit of the INRA in Avignon (France).
“Fertilisation can affect disease in three ways, explains Philippe Nicot. First of all, the minerals absorbed by the roots are used in plant cells. If we supply a lot of nitrogen to the plant, the leaves will generally become enriched in this element, whether it is in the form of minerals or proteins. Pathogenic fungi and insect pests may then find themselves with a richer substrate at their disposal.”
Secondly, fertilisation can also affect the defence mechanism of plants. Fertiliser composition and amounts applied can either positively or negatively influence the production of certain plant compounds that are toxic for pests or pathogenic agents. It can foster the reinforcement of cell walls, providing the plant with a better resistance to external attacks. Finally, on a third level, if plant growth is too luxuriant then the leaf micro-climate can become more humid, which favours the development of several diseases.
The fertilisation rate seems to be a key factor of success: at small dosages (for example nitrate concentrations between 0.5 and 2 mMol/L), the strawberry leaves treated with the biological control agent Serenade Max had lesion sizes that were clearly smaller than those observed on plants that received rates between five and ten times greater.
The strawberry plant is not the only one being studied. Philippe Nicot and his collaborators have also observed favourable fertilisation effects on tomato plants against Botrytis cinerea. “The data were obtained using two other biological control agents (two fungi), whose hypothetical mode of action does not include induction of resistance in the plant”, states the INRA researcher.
Currently, a big French national project (called FertiLég-FertiPro) involving the laboratory of Philippe Nicot, collaborators from other INRA research units and others involved in development and applied research is on the way to evaluate the interest of combining responsible fertilisation and the integrated protection of vegetable crops. “In order to go beyond the first laboratory studies, adds the researcher, we must identify and evaluate the possible collateral effects and test the strategies in the field while taking into account the constraints of farmers.” These constraints are numerous: one must evaluate the impact on a crop’s sensitivity to its main bioagressors, and not only against one disease, while also taking into account the impact on production costs, profitability and the quality of the harvested produce.


Dr Philippe C. Nicot
INRA - Unité de Pathologie végétale
F-84143 Montfavet (France)
Tel: +33 4 32 72 28 59