Biology, epidemiology

The Penicillium spp. have comparable biological characteristics. They often live as saprophytes on the various organs of the vine and in its environment, becoming opportunistic pathogens when the physiological state of the berries is modified (presence of wounds, advanced maturity, etc.).

• Storage and sources of inoculum

They are present in the majority of vine production areas in the world; they are found in many soils, on plants and on the most diverse plant debris. A good number of them are part of the phylloflora of the vine: they are found on the leaves, the fruits, in the bark, and for some in the weathered wood of vines affected by eutypiosis or esca for example.
P. expansum , like many other Penicillium spp., Is naturally present in the soil and on the various organs of the vine on which it is not uncommon to isolate it. It is preserved there in its mycelial form or in the state of spores.

• Plant penetration and host invasion

These fungi penetrate berries mainly when ripe, in several ways:
- directly through the cuticle in the presence of exudates;
- by contact from rotten berry to healthy berry;
- through the stomata, lenticels and microcracks, various injuries such as damage linked to pathogenic insects or fungi, physiological micro-bursts, bird pecks or solar burns;
- secondarily to attacks by B. cinerea , on gray mold, on and in the heart of the clusters.
Subsequently, their mycelium grows very extensively, growing in all directions inside the flesh which gradually degrades.

• Sporulation and dissemination of the fungus

P. expansum (Figure 1) like other species Penicillium (Figures 2 and 3), sporulates readily on rotten berries in the form of spore pads. These carry very many conidiophores generating conidia numbering in the millions. As soon as they reach maturity, they separate easily and float in the air for a while before falling back and initiating new contaminations.

• Factors influencing the development of fungi

The species that are Penicillium subservient to the vine appreciate heat and humidity. For example, the conidia of P. expansum have a germination optimum which is between 20 and 25 ° C in the presence of humid conditions. The growth of its mycelium stops above 30 ° C. This fungus only attacks berries in the ripening phase.