BEHAVIOUR OF PARASITICAL RELATIONSHIPS BETWEEN PHIALOPHO-RACINERESCENS AND THE CARNATION

The biological characteristics of this parasite, the conditions of its maintenance in soil, the eventual role played by intermediate hosts in the survival and multiplication of inoculum are studied. Parasite invasion of the host at the level of the root system is possible either by the mycelium or by direct penetration of spores through spontaneous wounds of the roots leading into the xylem vessels of the low part of the stem. From that time, the parasite settles down in the vessels very slowly at the beginning, then more and more quickly. Its presence stimulates living cells of the xylem: the "vessel associated cells" which develops a strong metabolic activity leading to the elaboration of "gums" and to synthesis of parietal constituents which thicken the walls. Consequently the vertical and transversal transfers of the sap are decreased and may be the major cause of the wilt. Evidences for the marked increase of "vessel associated cells" metabolic activity show that further investigations aiming to inhibit the involved stimulation could be very productive.

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