Screening of Cucurbita germplasm for ToLCNDV resistance under natural greenhouse conditions

In 2012, a new severe disease was observed that affected zucchini and other cucurbit crops in SE Spain. The identified causative agent was Tomato leaf curl New Delhi virus (ToLCNDV), a begomovirus with a bipartite genome of single-stranded DNA that was previously reported to affect various crop species of the Solanaceae and Cucurbitaceae in India. To identify sources of resistance in Cucurbita to this virus, we performed a screening of 143 accessions under natural infection with viruliferous whiteflies in a greenhouse at Almeria, Spain. The accessions were mostly C. pepo and C. moschata, selected from the germplasm banks at the University of Almeria in Spain (BSUAL), and the Newe Ya'ar Research Centre in Israel. Symptoms of ToLCNDV were assessed by a scale ranging from 0 to 4 in two replications of 6-8 plants at 21, 28 and 35 days after inoculation (dai). In the most promising accessions, tolerance was also assessed by a PCR-based diagnostic method to identify the presence of the virus in the apical shoot of the plants at 28 and 35 dai. Most of the inoculated accessions were susceptible to ToLCNDV. Severe symptoms were found in most C. pepo accessions at 35 dai, but five accessions showed some tolerance, expressed as a delay in the appearance of symptoms and their reduced incidence. Two C. moschata accessions remained asymptomatic and accumulated no virus in the plant apex during the entire essay.