Mechanical transmission of Tomato leaf curl New Delhi virus to cucurbit germplasm: selection of tolerance sources in Cucumis melo

Cucurbits are major crop species, including fruits and vegetables cultivated worldwide that supply essential vitamins and minerals to current diets in developed and developing countries. Viral diseases are main factors affecting cucurbits cultivation. The most widespread and damaging have been aphid-borne viruses belonging to the Potyviridae family. Whitefly-transmitted begomoviruses (Geminiviridae) have been identified more recently in different cucurbit species. A severe outbreak of Tomato leaf curl New Delhi virus (ToLCNDV) occurred in pumpkins and melons in the main production area of Southern Spain in 2012–2014. We developed a mechanical inoculation method to facilitate the screening of germplasm against this virus. Mechanical transmission with this method was confirmed in 4 genera and 13 species of the family, including the main crops, cucumber, melon, watermelon and pumpkins, and also crop-related exotic germplasm (landraces and wild species) used for cucurbits breeding. Diversity in the response was observed within and among species. Tolerance to mechanical transmission of ToLCNDV was identified in melon, within Cucumis melo subsp. agrestis var. momordica and in wild agrestis accessions. All the tolerant accessions came from India, the country in which this virus was firstly reported. Some of these accessions have been previously reported to be tolerant or resistant to other viruses and as they are fully crossable to commercial melons, they are good sources to develop new melon varieties with tolerance to ToLCNDV.