Characterization of Penicillium s.s. and Aspergillus sect. nigri causing postharvest rots of pomegranate fruit in Southern Italy.

Abstract

Most of diseases of pomegranate fruit are caused by fungal pathogens, which provoke postharvest yield and economical losses. Aspergillus and Penicillium sensu lato (s.l.) are the main wound pathogens of pomegranate fruit. In the present investigation, the populations of Aspergillus and Penicillium s.l. isolated from pomegranate fruit in Southern Italy were characterized. Since the morphological identification of species belonging to these genera is laborious, molecular approaches, such as PCR and High-Resolution Melting (HRM), were used. Particularly, a specific primer pair was designed to discriminate, within the Penicillium s.l. population, Penicillium sensu stricto (s.s.) from Talaromyces strains. Then, a new HRM assay for species identification within Penicillium s.s. according to SNPs present in a portion of the beta-tubulin gene was set up. Similarly, Aspergillus sect. nigri population was characterized arranging a HRM assay, whose primer pair was designed on a portion of the calmodulin gene. According to these assays, 10% of the Penicillium s.l. population proved to be made up of Talaromyces biverticillius strains. Furthermore, six species of Penicillium s.s. (P. adametzioides, P. brevicompactum, P. citrinum, P. glabrum, P. pagulum, and P. johnkrugii) and four of black aspergilli (A. tubingensis, A. welwitschiae, A. japonicus, and A. uvarum) were identified; all species belonging to both genera disclosed different incidences in postharvest rotted pomegranate fruit. Moreover, since Aspergillus and Penicillium are potentially producers of mycotoxins, like ochratoxin A and fumonisins, the presence/absence of genes involved in mycotoxin biosynthetic pathways was tested. Some Aspergillus strains belonging to species A. welwitschiae proved to possess fumonisin genes. The setup of molecular tools to characterize Penicillium s.l. and Aspergillus sect. nigri species infecting pomegranate fruit after harvest is of paramount importance for their effective control, even more considering the ability of these fungal genera to produce mycotoxins, which are hazardous for human health and potentially present also in by-products.