Tomato leaf curl New Delhi virus and other alien or emerging geminiviruses, a serious threat to vegetable production in Italy and Jordan

Project leaders

Gianpaolo Accotto, Ghandi Anfoka

Agreement

GIORDANIA - HCST/NCRD - The Higher Council for Science and Technology /National Centre for Research and Development

Call

CNR/HCST-NCRD biennio 2018-2019 2018-2019

Department

Biology, agriculture and food sciences

Thematic area

Biology, agriculture and food sciences

Status of the project

New

Research proposal

Vegetables are essential components of the Mediterranean diet and constitute important source of income for countries in the Mediterranean basin. Thanks to mild climatic conditions, use of protected crops and irrigation, many vegetables are available all year round for local consumption as well for export. This continuous planting facilitates the establishment and perpetuation of pests and diseases. Of particular relevance are viruses and their vectors, since no remedies are available to cure plants from viruses, and their vectors -usually insects - have developed resistance to many insecticides.
Viruses are major constraints to crop yield. Moreover, the increased exchange of planting materials facilitates the emergence and spread of new viruses.
Geminiviruses rank among the top of the most important plant viruses causing serious diseases in tomato, bean, squash, melon, watermelon, cassava and cotton, especially in warm and subtropical regions of the world. In the Mediterranean area, some geminivirus species are responsible for the notorious TYLCD (tomato yellow leaf curl disease), which spread from East to the rest of the countries in the 80' and 90', destroying tomato crops in many countries.
More recently, some cucurbitaceae are being seriously damaged by a number of new geminiviruses, now present in some countries but absent in others (Lapidot et al, Virol J 11:181, 2008). They are Squash leaf curl virus (SLCV), Watermelon chlorotic stunt virus (WmCSV), Tomato leaf curl New Delhi virus (ToLCNDV), Chickpea chlorotic dwarf virus (CpCDV).
The epidemiological state of the different viruses is continuously evolving, together with the changes in vector populations. Considering Italy and Jordan, ToLCNDV is present in Italy since 2015, where it caused marked crop losses in zucchini, but has not yet been reported in Jordan. On the contrary, at the moment SLCV (Al-Musa et al, J Phytopathol 156:311, 2008) and WmCSV are present in Jordan, but not in Italy. CpCDV ha been recently reported on watermelon in Tunisia (Zaagueri et al, Plant Dis 101:392, 2017), but not in Italy and Jordan so far.

Cucurbits are among the major vegetables grown in the Mediterranean basin, with more than 23 million tons; ranking third after tomatoes and potatoes. Four major species are cultivated, cucumber (Cucumis sativus), melon (C. melo), watermelon (Citrullus lanatus), and different squash species (Cucurbita pepo, C. moschata, and C. maxima), with a great diversity of types and cultivars adapted to local demands for the consumption of raw or cooked fruits.
ToLCNDV infects several crops mainly of the Solanaceae and Cucurbitaceae families. Until 2012, the virus was confined to India and other Asian countries, where it infected tomato, aubergine, chili pepper, potato and several cucurbits. In the last years, zucchini suffered severe outbreaks caused by ToLCNDV in Spain (Juarez et al, Plant Dis 98:857, 2014) and, since 2015, also in Italy and Tunisia (Panno et al, New Dis Rep 33, 2016; Mnari-Hattab et al, New Dis Rep 31, 2015). ToLCNDV is in the EPPO Alert List of emerging viruses in the Euro-Mediterranean region (https://www.eppo.int/QUARANTINE/Alert_List/viruses/ToLCNDV.htm). Like the other begomoviruses, it is transmitted by the whitefly Bemisia tabaci in a persistent manner.

ToLCNDV induces yellow mosaic, leaf curling, vein swelling, and plant stunting, accompanied by skin roughness and longitudinal cracking on cucurbit fruits. When the infection occurs at an early stage, plants can be severely stunted and fruit production is significantly reduced, if not suppressed.
Phylogenetic analysis of ToLCNDV isolates revealed a highly heterogeneous population, with no evident geographical, plant host or year-based phylogenetic groups. Virus isolates from Spain seem to be evolved by recombination and populations more adapted to cucurbits or tomato seem to diverge. In the Indian subcontinent, ToLCNDV is often accompanied by betasatellites that might affect its pathogenicity.
Control measures against ToLCNDV are limited and mainly rely on vector control, cultivation in greenhouses, elimination of infected materials. Presently, no resistance or tolerance to ToLCNDV has been introduced in cultivated in cucurbits (Sáez et al, .Ann Appl Biol 169:91, 2016).
The recent advances in understanding the response of plants to virus infection have paved the way to exploit metabolic pathways used by plants to counteract virus invasion and replication. Among these, the use of interfering RNA molecules capable to induce an antiviral response, also known as "double-stranded RNA (dsRNA)-based vaccination", is a promising strategy based on RNA interference, a sequence-specific conserved regulatory mechanism mediated by dsRNA homologous to the silenced gene. Several dsRNA molecules have been designed and tested under laboratory conditions to reduce the impact of specific viruses.A single preliminary report specific to ToLCNDV indicates that resistance can be induced, at least in laboratory conditions (Singh et al, Plant Pathol 16:724, 2015). However, the delivery of such dsRNAs requires further improvement, and the aspects related to off-targets and bio-safety need also to be investigated.
COMPETENCE OF THE TEAM: The scientists responsible and their collaborators have long-time experience in plant virology (field and molecular)
IMPACT: the joint activities will produce an updated knowledge of the spread of ToLCNDV and other geminiviruses in cucurbits in Italy and Jordan, countries that share similar phytopathological challenges with new viruses. Clear examples have been the epidemics of TYLCV and TYLCSV in the last decades. Data on biodiversity of strains and their host range will help understanding risks for different crops. The attempts to limit ToLCNDV spread by a biotechnological approach will pose the bases for a stronger scientific collaboration, based on a common important issue, between the two countries in the future.

Research goals

Due to the recent ToLCNDV epidemic on zucchini in Spain and Italy, and SLCV/WmCSV epidemics on cucurbits in Jordan and surrounding countries, the focus will be on geminiviruses infecting zucchini and other cucurbitaceae. A first goal will be to obtain updated information about which geminiviruses are present in cucurbitaceae in the two countries. In the second year experiments will be devised and conducted to evaluate if a stable, effective and safe protection can be obtained against ToLCNDV using dsRNA-based vaccination.
Specific objectives of the project will be:
(I) surveying cucurbit crops for virus symptoms in both countries and collecting sample of the cultivated species and weeds nearby.
(II) Searching for geminiviruses by molecular techniques, such as Rolling Circle Amplification, a non-targeted technique capable of detecting all circular DNA molecules.
(III) Obtaining sufficient genomic data for taxonomic classification of the geminiviruses
(IV) Build up genetic relationships between virus isolates found in the two countries and compare them with previously reported ones.
(V) devise strategies for dsRNA-based vaccination against ToLCNDV to reduce crop losses.
(VI) evaluate the feasibility to use biodegradable and biocompatible nanocapsules to deliver active dsRNA molecules
(VII) investigate the stability of the delivery complex containing the dsRNAs, and its biosafety.
(VIII) evaluate, by an in silico approach, the risk of dsRNAs off-targets.

Last update: 08/06/2025