Early detection of Aspergillus carbonarius and A. niger on table grape: a tool for quality improvement
Résumé
Aspergillus carbonarius and A. niger aggregate are the main fungal contaminants in table grapes. Besides their ability to cause the Black rot, they can produce Ochratoxin A (OTA), a mycotoxin that has attracted increasing attention worldwide. The objective of this work was to set up a simple and rapid molecular method for the early detection of both fungi in table grapes before fungal development becomes evident. PCR-based assays were developed by designing species-specific primers based on the polyketide synthases (PKSS) sequences of A. carbonarius and A. niger that have recently been demonstrated to be involved in OTA biosynthesis. Three table grape varieties (Red globe, Crimson seedless and Italia) were inoculated with A. carbonarius and A. niger aggregate isolates strains producing OTA.. Samples were collected 0, 3, 6, 9 and 12 days after inoculation. The extracted DNA extracted from control (non-inoculated) and from inoculated grapes was amplified by PCR using ACPKS2F-ACPKS2R for A. carbonarius and ANPKS5-ANPKS6 for A. niger aggregate. Both primers allowed a clear detection even in symptomless samples. Since the high specificity and sensitivity of PCR-based methods, they are considered to be a good alternative to traditional diagnostic means for the early detection of fungi in complex matrix. The results obtained could be useful for the definition of a "quality label" for tested grapes to improve the safety measures taken to guarantee the production of fresh table grapes.
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