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Development of a Prototype model for A. carbonarius growth and OTA production

All available information were used to draw the relational diagram of A. carbonarius-grape pathosystem. The other fungi were not considered because of minor interest.
The inoculum was always observed on berries; it was not considered a limiting factor and its quantification was considered not relevant.

Spore germination has been studied on grape juice agar, grape flesh and grape skin and interesting equations were found able to predict correctly germination. The basic function was a logistic and it was fitted to data considering 2 factors, time and temperatures, or 3 factors, when relative humidity was added.

Growth rate of A. carbonarius in function of temperature is available and it will be improved, if necessary with further data collected in different humidity conditions.
The mycelium of A. carbonarius can stay on skin and colonise berries or grow inside and infect berries. Colonisation and infection rates are influenced by the same variable. Temperature is always a relevant factor because, as described before, influence the growth rate, but berries status and grape varieties are definitely relevant.

Taking about berries status (BS) the main aspect regards presence/absence of damages on skin. In case of damages, it is very easy for the fungus to develop inside the berry and it was confirmed in many trials that infection is very rapid. Many factors can determine skin damages, but rain (R), especially during ripening, and pest and disease (P&D) presence play a main role. A correlation was found between OTA content in berries and Lobesia botrana damages, probably related to both wounds and spore dissemination. Larvae probably contribute to spore dispersal; they can act as vectors, trapping conidia in the cuticle ornamentation, and facilitating rapid penetration tunnelling berries.

Among pathogens, powdery mildew seemed the most conducive for black aspergilli. Infected berries often are misshapen or have rusty spots on the surface and severely affected fruit often split open, mainly during ripening when the inoculum of black aspergilli is more relevant.

Grape variety is a further relevant factor that can favour berries infection and its relevance was shown both in vitro and in field trials. This factor needs to be studied deeper, because the reasons that make a variety more or less susceptible were not understood.

It is not easy to quantify colonisation or infection of berries, but a yes/no response seem sufficient to run the model, at least for the first validation.
Ochratoxin A seems more concentrated in the outer part of the berry, in the skin and very close layers, but till now its production without berry infection was not demonstrated. For that reason, only infected berries were considered to quantify OTA production.

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Università Cattolica del Sacro Cuore
Via Emilia Parmense 84
29100 PIACENZA
Italy
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