Focus on biodiversity: looking for sustainable approaches to manage Tomato Leaf Curl New Delhi virus on cucurbits

Tomato leaf curl New Delhi virus (ToLCNDV) is an emerging begomovirus listed in the EPPO Alert-list 2 and reported in 2015 for the first time in Southern Italy on Sicilian courgette. The virus is persistently transmitted by Bemisia tabaci, and it is particularly harmful on cucurbits, causing 100% production losses. A sustainable and environmentally friendly approach is needed to counteract the viral disease. Local cucurbit ecotypes were screened to assess tolerance levels, and Cucumis melo cv. Barattiere was found to be the most tolerant, showing no detectable disease symptoms and very low levels of viral DNA accumulation using a time-course quantitative dot-blot assay. This local variety was then used as a potential rootstock to achieve levels of tolerance in commercial cucurbit varieties. Different graft combinations of susceptible and moderately susceptible cucurbit genotypes onto C. melo cv. Barattiere plants showed a generalized delay in viral symptom appearance and less severe disease than those observed in non-grafted counterparts. Consistently, the viral DNA accumulation in all grafted combinations showed a significant reduction between 11 and 28 days after inoculation. RNA-Seq analyses at 11 dpi were performed to investigate the transcriptome profile of C. melo cv. Retato Standard F1 grafted onto C. melo cv. Barattiere used as rootstock. Experimental open fields have been established in areas exposed to high viral inoculum to evaluate the response of grafted plants to counteract ToLCNDV infection. Furthermore, the setup of a portable real-time PCR-based diagnostic assay is in progress to provide a rapid and quantitative tool.