Characterization of a Diaporthe toxica Strain: Growth, Spore Formation, Phomopsin-A, and Alkaloids Production on Lupins

The growing interest in vegetable proteins, namely those derived from lupins, has raised concerns over potential safety risks associated with these food products. Lupin serves as the main host for the mycotoxin-producing fungus called <i>Diaporthe toxica</i>. This species, which is associated with animal diseases, has been scarcely characterized. Recently, phomopsin-A (PHO-A), the main mycotoxin produced by <i>D. toxica</i>, was found to be harmful to humans. Therefore, this study aimed at characterizing <i>D. toxica</i> growth and spore formation both in vitro and on lupin samples. In addition, the production of PHO-A and alkaloids was investigated on lupin beans by using three different inoculation methods. Particularly, growth and spore production were evaluated on different media, while PHO-A and alkaloid production were determined by means of µSPE extraction followed by UHPLC-MS/MS and HPLC-MS/MS, respectively. The results have demonstrated differences in growth on different media, with potato and oat-flakes-based media being the best options. Conversely, <i>D. toxica</i> was not able to produce spores on agar media, but only on lupin beans. Moreover, a thorough analysis of PHO-A production revealed an increase over time, reaching values up to 1082.17 ppm after 21 days on artificially rehydrated samples. On the other side, the analysis of alkaloids revealed impressive results, as this species produced great quantities of the quinolizidine alkaloids (QA) that are normally present in lupin seeds such as lupanine, sparteine, multiflorine, and hydroxylupanine. On balance, considering these results, different metabolic pathways were demonstrated in <i>D. toxica</i>, which are not adequately described in the existing literature. These data are of paramount importance to deepen the knowledge about a fungal species that is important to ensure the safety of lupin and lupin-based products.