Abstract
Tomato leaf curl New Delhi virus (ToLCNDV) is a bipartite begomovirus (family
Geminiviridae) first reported in India and its neighbouring countries. ToLCNDV
severely affects zucchini crop (Cucurbita pepo) in the main production areas
of Southern Spain since 2012. This emerging begomovirus is a serious threat
to this and other cucurbit crops. Breeding resistant cultivars is the most
promising method for disease control, but requires the identification of sources
of resistance in the Cucurbita genus. In this work, we screened for ToLCNDV
resistance a large collection of Cucurbita spp. accessions, including landraces and
commercial cultivars of the main cultivated species, C. pepo, Cucurbita moschata
and Cucurbita maxima and wild species. The screening was performed using
mechanical and whitefly inoculation. The level of resistance was assessed by
scoring symptom severity and bymeasuring the virus content with quantitative
polymerase chain reaction in selected genotypes. Diversity in the response
was observed within and among species. Severe symptoms and high viral
amounts were found at 30 days after mechanical and whitefly inoculation in
C. pepo, in all accessions belonging to the Zucchini morphotype and to other
morphotypes of both subspecies, pepo and ovifera, and even in the wild relative
Cucurbita fraterna. C. maxima was also highly susceptible. This species showed
characteristic symptoms of leaf decay and intense yellowing, different from
those of mosaic, curling and internode shortening found in C. pepo. The only
species showing resistance was C. moschata. Four accessions were symptomless
or had some plants with only mild symptoms after three independent rounds
of mechanical inoculation with different inoculum sources. Two of them also
remained symptomless after virus inoculation with viruliferous whiteflies.
ToLCNDV was detected in these asymptomatic accessions at 15 and 30 days
post inoculation, but viral amounts were much lower than those found in
susceptible genotypes, suggesting a high level of resistance. The symptoms in
the susceptible accessions of this specieswere also different, with a characteristic
leaf mottling, evolving to a severe mosaic. The newly identified C. moschata
resistant accessions are good candidates for breeding programmes to avoid the
damage caused by ToLCNDV.
