**1. Introduction**

*Fusarium verticillioides* (Sacc.) Nirenberg is a member of the *Gibberella fujikuroi* species complex, also called *Fusarium fujikuroi* species complex (FFSC), a group of 40 closely related *Fusarium* species defined by morphological traits, sexual compatibility and DNA-based phylogenetic analysis [1,2].

In particular, *F. verticillioides* belongs to the "African" clade of the FFSC [3], and it is the main causal agen<sup>t</sup> of *Fusarium* ear rot of maize (*Zea mays* L.) [4,5]. This fungus has been reported worldwide and, in particular, it prevails in drier and warmer climatic regions [6,7] such as those present in temperate, semitropical and tropical regions including European [4], Mediterranean [8], African [9] and Middle

Eastern [10] maize-growing areas. For example, *F. verticillioides* was the species isolated more frequently from maize kernels harvested in Italy [11–13], Spain [14–16], Egypt [17–21] and Iran [22]. This is also one of the species able to biosynthesize the secondary metabolites fumonisins [23]. Specifically, *F. verticillioides* is considered the main fumonisin producer; therefore, this is the most important species associated with fumonisin contamination of maize grains [24]. Fumonisins occur worldwide in maize, including Mediterranean [4,8,24,25] farming areas, where this is one of the most widely cultivated crops [26,27]. Fumonisin accumulation in maize grains can occur in the field, following preharvest infections, and possibly continue during grain storage [28].

Contaminations strongly impair maize grain quality because of the negative impact on animal and human health [29]. Fumonisin mycotoxins can be divided into four main groups, with the most abundant fumonisins found in nature included in the B group: fumonisin B1 (FB1), fumonisin B2 (FB2) and fumonisin B3 (FB3). Among B analogues, FB1 is the most detected fumonisin in maize as well as the most toxicologically active [24,30]. In fact, after ingestion, fumonisins may cause a wide range of toxic effects, especially towards liver and kidneys [31–35]. For this reason, the European Commission has established maximum limits for the sum of FB1and FB2in maize for human consumption [36,37].

The amount of fumonisins found in maize kernels is also dependent on the toxigenic ability of the *F. verticillioides* populations occurring in a certain cultivated field or in a specific geographic area [38]. In fact, within the *F. verticillioides* species, fumonisin production commonly varies quantitatively because of the different strain abilities to biosynthesize different levels of these mycotoxins [15,24,39–41]. The amount of fumonisins produced may also vary in quantity depending on substrate [42], biotic and abiotic factors [43] as well as on the relative expression of the genes involved in the biosynthetic pathway [44]. In fact, fumonisin production in *F. verticillioides* is regulated by the *FUM* biosynthetic gene cluster [45], and some of the differences between strains can be explained by *FUM* gene sequence differences [46,47]. Thus, it is very important to determine the variations of fumonisin production by *F. verticillioides* to understand the biosynthetic potential of a certain population in a specific cultivation area.

The characterization of fumonisin biosynthesis by *F. verticillioides* strains isolated from different geographic areas has been often coupled to the study of the genetic structure of these populations to investigate the degree of genetic diversity between the different strains within the same species [44,48–50]. This can provide an important insight on the relationships, the variations and/or the similarities among strains originating from various regions as well as on the possible correlations between genetic variability and different fumonisin production [38,51–54]. Analyses of fumonisin biosynthesis and/or molecular characterization of *F. verticillioides* strains have been conducted in populations from different countries such as Argentina [55], Brazil [38,41,44,49], Italy [50], Iran [22,52], Ethiopia [53] and Nigeria [54].

A similar approach was adopted in the present work to characterize selected *F. verticillioides* strains originating from five Mediterranean countries to simultaneously compare them in a wider geographical context by evaluating their in vitro fumonisin production and genetic profile. Specifically, the main objectives of the present study were to:

