Identifying the phytopathogenic agents : methods of diagnosis

Diagnosis covers two complementary aspects:

•  The detection of a pathogen and the estimation of the level of infection of a plant are necessary steps as far as quarantine and certification activities are concerned. Detection requires that the techniques used are sensitive enough to reveal a latent infection in plants without any visible symptoms.
   No existing detection test can prove the absolute absence of contamination. “Zero tolerance” concerning the importation of plant products can only be guaranteed by a complete embargo. 
•  The identification of the agent responsible for the symptoms on a plant is the preliminary step in the choice of control methods. It requires a close observation of the symptoms in order to collect a maximum of information regarding the development of the disease. The analysis of these data must lead to the formulation of hypotheses as to the identity of the causal agent. Laboratory tests are necessary to confirm those hypotheses.

Each of these aspects is carried out in two steps :

The first step concerns the analysis of the symptoms and the circumstances related to their appearance and the development of a particular disease. This step makes it possible to formulate hypotheses as regards the pathogen concerned.

The second step consists in the validation of these hypotheses through precise and specific laboratory techniques.

Note : The diagnosis will be made easier by a prior knowledge of the main diseases that can affect the crop concerned at the various stages of its growth and under different conditions.

Source : Extract from Phytopathologie, De Boeck