Grafting to manage tomato leaf curl New Delhi virus in cucurbits.

Tomato leaf curl New Delhi virus (ToLCNDV) is an emerging begomovirus (Geminiviridae family) listed in the EPPO Alert-list 2, present in the Mediterranean area and in Italy, where it was reported in 2015 in Sicilian courgette and since then its recurrent outbreaks generated justified concern among growers. The virus is particularly harmful in cucurbits, where it causes 100% production losses, thus a sustainable and environmentally friendly approach must be adopted. Genetic resistances have been identified in Cucurbita moschata and Luffa cylindrica, but the graft could provide a faster and more flexible solution inducing tolerance rather than resistance, as shown in tomato crops by grafting susceptible commercial tomato varieties onto the tomato wild ecotype Manduria (Ma). Here we report results of a screening among twenty-one local cucurbit ecotypes to evaluate tolerance levels against mechanical transmission of ToLCNDV. Results will lead to the identification of potential rootstocks to attain suitable levels of tolerance against the virus in commercial cucurbit varieties. Plants were challenged with ToLCNDV isolated in Apulia and observed for disease symptoms development and viral DNA accumulation by quantitative dot-blot assays at 14 and 28 days after inoculation. C. melo var. Retato standard (F1 commercial hybrid) and C. pepo var. Scuro di Milano proved the most susceptible, whereas C. melo var. Barattiere and C. pepo accession 5 the most tolerant. Tolerant plants did not show disease symptoms and very low level of virus accumulation, suggesting their use as rootstocks of grafted cucurbits against ToLCNDV outbreaks.