3.8.2
PHYTOPHTHORA SPP. AND GEOTRICHUM CANDIDUM IN THE HYDROPONIC FORCING OF CHICORY ROOTS: DETECTION, EPIDEMIOLOGY AND CONTROL

N DEMEULENAERE1, R SARRAZYN2, P DE CLERCQ1, S MESTDAGH1 and M HOFTE1

1Faculty of agricultural and applied biological sciences, Laboratory of Phytopathology, University Gent, Belgium; 2POVLT, Beitem-Rumbeke, Belgium

Background and objectives
In Belgium, 1412 farms are involved in the production and forcing of chicory (Cichorium intybus var. foliosum). The total production of chicory crops is estimated at 93,500 tons per year. The cultivation of chicory evolved a lot during the past 20 years: forcing of the roots in a pit, with or without a casing layer, is almost completely replaced by a hydroponic system. The last years however, hydroponic forcing of chicory roots has to deal with severe root rot problems. Phytophthora cryptogea, Phytophthora erythroseptica (members of the Oomycota group) and Geotrichum candidum (member of the Mitosporic fungi) have been isolated from diseased roots but it is still unclear however which fungus is the main pathogen. To study the epidemiology of these fungi, simple and consistent techniques for detection in soil and water were developed and artificially infections were carried out.

Results and conclusions
Since Phytophthora might be present in soil that sticks on the roots after harvest, a bait method was developed using pieces of chicory roots [1]. The detection of G. candidum in soil can be done by enrichment and isolation in media containing novobiocine. For the detection of Phytophthora in water, the usefulness of a commercial ELISA detection kit was tested, but the detection limit was 105 zoospores/ml. Because of this low sensitivity also a detection method using nested PCR was used for the detection of P. cryptogea in water [2].

Infection experiments showed that both Phytophthora strains could readily infect chicory roots: when 2.30.2 g mycelium dry weight or 104 zoospores were mixed in 250 ml water, severe root rot symptoms were observed after 9 days. With Geotrichum candidum, however, it was not possible to infect roots even when 106 spores or injured roots were used. These results show that Phytophthora is the main pathogen and that Geotrichum is an opportunistic pathogen, probably associated with bad hygienic conditions. Preliminary results showed that a field treatment with systemic fungicides could already prevent a lot of problems. Alternatively biological control with phenazine producing Pseudomonas strains seems to be very promising.

References
1.Erwin DC, Ribeiro OK, 1996. The American Phytopathological Society, St. Paul Minnesota, 562p.
2.Bonants P, Hagenaar-de Weerdt M, Gent-Pelzer M, Lacourt I, Cooke D, Duncan J, 1997. European journal of plant pathology, 103, 345-355.