Emergence of tomato leaf curl New Delhi virus in Italy: estimation of incidence and genetic diversity

Tomato leaf curl New Delhi virus (To LCNDV ) is a bipartite begomovirus (family Geminiviridae ) identified for the first time in 1995 in Asia, from where it spread into several countries of the Mediterranean basin. To LCNDV was found in Spain in 2012, and subsequently in Tunisia and Italy. The first outbreak in Italy occurred at the end of 2015 in Trapani province (Sicily) on zucchini squashes. Then in 2016, To LCNDV was found in infected zucchini plants in Campania, Lazio and Sardinia regions, and in 2017 in Calabria. This study addressed the dispersion and genetic diversity of To LCNDV isolates in Italy. A total of 1400 plants were analysed. Phylogenetic analysis showed low variability among the Italian isolates, probably as a consequence of the recent introduction and rapid spread of this virus in Italy. Two statistically significant clusters were reported: one grouping only Italian isolates and the other grouping Italian, Spanish, Tunisian and Moroccan isolates. Furthermore, the highest incidence of To LCNDV was observed in Sicily, although the disease also appears to be critical in other Italian regions. In this work, a high efficiency of To LCNDV mechanical transmission into Cucurbita pepo , Cucumis melo inodorus and Cucumis melo cantalupensis has been demonstrated. The rapid spread of To LCNDV in the Mediterranean basin represents a threat for horticultural production, thus it is very important to develop suitable crop management practices, applying genetic resistance strategies and more restrictive phytosanitary measures.