Mycologia, ASCOMYCOTINA, HELOTIALES, SCLEROTINIACEAE .
Identification, Description, Biology, Epidemiology, Treatement, Possible misleading, Images
This parasite causes a grey down on the affected capitulum and stem while the leaves rather start drying out from the extremity. At the beginning of maturity light brown spots appear on the non floral side of the capitulum and if the conditions are favourable, rapidly turn into sporulating spots (grey conidial sporulation) visible on the floral side of the inflorescence (corolla). Black flat sclerotia deprived of medulla appear on the crop debris after harvesting or directly on the plants when harvesting is carried out too late.
The fungus persists through the winter on and in the soil as mycelium or sclerotia in the plant debris ; inside and outside the achene as mycelium.
In spring the overwintering forms of the fungus germinate and produce conidia which spread all over in the atmosphere and set on all sorts of plants. Conidial spreading by the wind is a chance event and does not induce a focus of infection in the crop. The fungus has a high number of reproductive cycles which increases even more when the weather conditions are favourable.
The presence of slightly senescent tissues (floral parts), pollen or lesions facilitates the settling of this saprophyte.
Conidial germination is possible on the florets in RH exceeding 85%. The optimum germination temperature is 18 . The colonisation of the florets is rapid but often undetectable ; the colonization of the totality of the tissues of the capitulum is much slower and the first symptoms on the abaxial surface only occur at the maturity of the capitulum.
The actual outbreak of the epidemic (rapid increase of the number of reproductive cycles of the fungus and generalized contamination of the whole crop) is mainly due to a succession of periods of high RH (>85%) and dryness.
Seed control is necessary in order to prevent damping-off.
Chemical treatment is complicated by resistance of the pathogen to certain active material.
Research on antagonist natural microorganisms has been carried out and it was found that Trichoderma harzianum provides satisfactory results and may be effectively combined with a traditional chemical treatment (in progress).
Sclerotinia sclerotiorum as long as the sporulating spots of B. cinerea are not covered by conidia : the characteristic "grey mould".
HYP3 on line : Species (scientific name), Diseases (common names), Glossary, Crops.