**1. Introduction**

The set of plants producing citrus fruits is composed of a large number of species from the *Citrus*, *Fortunell*a, and *Poncirus* genera. Among the main species are sweet oranges (*Citrus sinensis*) and bitter oranges (*Citrus aurantium*), mandarins (e.g. *Citrus reticulata*, *Citrus delicia*, *Citrus clementina*, *Citrus unshiu*, and *Citrus nobilis*), lemons (*Citrus limon*), limes (e.g. *Citrus latifoli*a, *Citrus aurantifolia* and *Citrus limettioides*), grapefruits (*Citrus paradisi*), pummelos (*Citrus maxima*), kumquats (*Fortunella* spp.), and trifoliate orange (*Poncirus trifoliata*). Fruits of commercial importance for human consumption are mainly from *Citrus* species. In a small proportion, *Fortunella* species (fruits known as kumquats) are also worthed. Moreover, several hybrids such as tangors (mandarin × sweet orange) and tangelos (mandarin × grapefruit) are also important commercially. On the other hand, *P. trifoliata* and its hybrids *Citrus* spp. are used only as rootstocks, not being edible [1].
