VIRTIGATION partners NRI, CSIC, Volcani Center and INRAE have assessed plant virus transmission dynamics by whiteflies and weeds.
Article by Marianna Granatier from the VIRTIGATION project
Whiteflies: major drivers of viral outbreaks
Researchers in the VIRTIGATION project have investigated the potential pathways for the spread of ToLCNDV by the Bemisia tabaci whitefly species complex. Furthermore, the project scientists explored the host range and transmission dynamics of weeds as hosts for ToLCNDV, but also ToBRFV. They detailed their findings in a recent report.
Whiteflies such as the Bemisia tabaci have become a major driver of plant disease outbreaks across the Mediterranean, as well as in tropical and subtropical regions. The Bemisia tabaci species complex exhibits unique biological and behavioural traits. It damages plants in two primary ways:
- Direct feeding, which leads to stunted growth and leaf yellowing, and
- Virus transmission, as it serves as a vector for nearly 500 plant virus species, posing a serious threat to global food security.
Two Bemisia tabaci biotypes have largely driven the global rise in begomovirus infections: B (MEAM1 species) and Q (MED species). While these biotypes have not overtaken native populations in India, the Q biotype has become widespread in Europe, where it plays a key role in the transmission of cucurbit leaf curl disease. Additionally, other whitefly species such as Trialeurodes vaporariorum have shown the ability to transmit ToLCNDV in India.
Estimating effectiveness of whiteflies on viral disease spread
India, long considered a center of origin for whiteflies, is home to several biotypes of Bemisia tabaci. As part of VIRTIGATION, NRI researchers in collaboration with UASB (in India) investigated the vector competence of Indian whitefly populations in transmitting ToLCNDV.
The study tested the transmission ability of seven Bemisia tabaci species: MED, MEAM1, Asia I, Asia II-5, Asia II-7, Indian cassava, and an outgroup from Nigeria.
Their results revealed that Indian whiteflies (particularly the Asia II-7) were significantly more efficient in transmitting ToLCNDV, achieving 100% transmission efficiency, compared to invasive biotypes such as MED (B biotype) and MEAM1 (Q biotype).
These findings support the theory of co-evolution between viruses, vectors, and host plants within the same geographic region. They also underscore the importance of targeting local whitefly populations in the development of effective virus management strategies.
Role of European whiteflies in the spread of TOLCNDV-ES
To assess the vector competence of Bemisia tabaci, specifically the MED and local SSA2 species, in transmitting the Spanish strain of ToLCNDV-ES, project researchers conducted transmission experiments from zucchini to Ecballium elaterium, an alternative host plant.
In the case of the MED species, their results showed inefficient transmission between zucchini and E. elaterium, suggesting that E. elaterium may act as a dead-end host. However, when they used zucchini as both the source and recipient plant, the VIRTIGATION scientists could observe a 50% transmission efficiency. Similarly, when they tested SSA2 as a vector for ToLCNDV-ES, they found that its transmission efficiency was comparable to that of MED.
These findings indicate that both the widespread MED and local SSA2 whitefly species are capable of spreading ToLCNDV-ES, emphasizing the need to monitor and manage both vector populations to effectively control virus outbreaks.
ToLCNDV transmission between zucchini plants by Trialeurodes vaporariorum
CSIC and INRAE further conducted experiments in Spain and France to evaluate the transmission potential of the Spanish strain of ToLCNDV-ES by the glasshouse whitefly Trialeurodes vaporariorum. Researchers used virus-infected zucchini plants and compared the results with those obtained using the known vector, Bemisia tabaci MED.
Despite multiple trials, Trialeurodes vaporariorum failed to transmit the virus, confirming that it is not a competent vector for ToLCNDV-ES. However, while it does not contribute to virus spread, T. vaporariorum remains a direct pest due to its feeding activity on crops such as tomato and cucurbits, which can still result in significant agricultural damage.
Host range of ToLCNDV-ES European strain
Moreover, VIRTIGATION researchers investigated the presence of alternative natural hosts of ToLCNDV in Spain and France. The scientists analysed 400 plant samples, representing 30 different species (e.g Achyranthes aspera, Datura stramonium) for ToLCNDV-ES using molecular hybridization and RCA/RFLP techniques. Among all tested species, they found E. elaterium to be the only plant found infected with ToLCNDV-ES. They subsequently molecularly identified, cloned and sequenced several isolates from E. elaterium.
To further assess potential reservoirs, project researchers tested a range of weed and cultivated plants commonly found in southeastern France for susceptibility to ToLCNDV through mechanical inoculation. They found that Bryonia dioica (bryony) and Datura stramonium (jimsonweed) are susceptible to infection and could serve as potential virus reservoirs.
While they confirmed E. elaterium to be infected, it does not support efficient virus transmission by whiteflies, suggesting it poses a limited epidemiological threat. In contrast, bryony and jimsonweed are capable of both harbouring and transmitting ToLCNDV to cucurbit crops, making them significant contributors to virus spread.
To mitigate early-season outbreaks and reduce the risk of new virus strains emerging, VIRTIGATION scientists recommend to remove these weed species from areas surrounding cucurbit fields.
Determining the host range of ToBRFV
Finally, Volcani Center researchers evaluated the reservoir potential of wild weeds for the rapidly spreading ToBRFV, by focusing on Solanaceae species that are common in Israel.
Through mechanical inoculation and a combination of detection methods (including qRT-PCR, ELISA, Western blot), the Volcani Center team identified three Solanaceae species as hosts of ToBRFV: Solanum nigrum, Solanum elaeagnifolium, and Solanum rostratum.
The Volcani Center findings highlight the role of wild solanaceous weeds as potential virus reservoirs, which could contribute to the persistence and spread of ToBRFV in agricultural environments.
Read here the deliverable “Reports on the role of different whitefly species and weed hosts on viral disease epidemics” produced by VIRTIGATION partners NRI, CSIC, Volcani Center and INRAE, which describes their research in more detail.
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