Biology, epidemiology

• Conservation, sources d'inoculum

Pilidiella diplodiella is mainly preserved thanks to its pycnidia formed on lesions present on twigs or stems, and on grape berries that have remained on some stems or fallen to the ground (figure 1). These pycnidia seem to be able to keep for several years in the vineyard without problems, therefore the soil, they are therefore the source of the primary inoculum.

Primary contaminations are often airborne; they involve conidia from pycnidia which are dispersed during rains, by splashing water and spray.

• Penetration and invasion

After the conidia germinate (at temperatures between 11-30 ° C), their germ tube enters berries or twigs via various wounds, probably also directly through the skin or epidermis. Mycelium gradually invades the tissues thereafter. It should be noted that contaminations on berries only take place between the "grain the size of a pea" and "early veraison" stages. The incubation period lasts from 3 to 8 days depending on the climatic conditions, the organ attacked and the grape variety.

• Sporulation and dissemination

On all colonized organs, the fungus produces numerous spherical pycnidia (figure 2) more or less flattened, gradually turning brown. For example, on each berry of grapes one can count up to at least 200 of them. These fungal structures produce several hundred spores (figure 3) which are extruded from the pycnidia by the ostiole, in the form of mucilaginous matrices. The conidia will be at the origin of the secondary contaminations which will be ensured especially by the rains, the splashes of water, the workers working when the vegetation is wet, etc.

• Conditions favorable to its development

Like many aerial fungi, P. diplodiella is particularly fond of humid and rainy periods. The development of this fungus on the grapevine seems to be favored by the presence of wounds caused by the fall of hailstones on berries and grapevine shoots during the summer, and even by various other berry pests. This statement seems a little too restrictive and does not fully reflect the parasitic potential of the latter. Indeed, it seems probable that it can attack the grapevine during favorable climatic conditions, and this in the absence of hail in particular.

The optimum temperature for the development of the fungus would be between 22-27 ° C.

Different species Vitis do not appear to have the same sensitivity to white burping.

Synoptic of the development of P. diplodiella