Taxonomy: Geminiviridae, Begomovirus, Squash leaf curl China virus
The most up-to-date and complete virus taxonomy is available on the International Committee on Taxonomy of Viruses webpage.
Squash leaf curl China virus (SLCCNV) is an emerging virus of cucurbits in Asia. It has been associated with curling, distortion, mosaic, and yellowing in many cucurbits, including cantaloupe and muskmelon, cucumber, luffa, pumpkin, squash, watermelon, and several types of gourd, and can cause significant economic losses (Venkataravanappa et al., 2021, 3 Biotech 11). The virus was first reported in China in 1995 in association with leaf curling and distortion in cucurbits (Hong et al., 1995, Sci China B 38). The virus was subsequently associated with similar symptoms in the Philippines in 2001 (Tsai et al., 2007, Plant Dis. 91) and Vietnam in 2003 (Revill et al., 2003, Arch Virol. 148.
The species SLCCNV is comprised of two strains, China (SLCCNV-CN) and India (SLCCNV-IN), named for the locations from which they were originally described (Fauquet et al., 2008, Arch. Virol. 153). There is also evidence of adaptation of strains to cucurbit species. For example, while most SLCCNV isolates do not infect melon, a recently described isolate of SLCCNV-CN is highly virulent in melon (Wu et al., 2020, J. Integr. Agric. 19). Additionally, evidence of recombination within SLCCNV-IN was recently reported in India, where an isolate of SLCCNV-IN was found to be highly virulent in summer squash (Venkataravanappa et al., 2021).
Thus far, SLCCNV has not been reported in the Western Hemisphere. The virus is transmitted by the whitefly Bemisia tabaci; this supervector has worldwide distribution and is widely prevalent in many cucurbit-producing regions, including those in the United States. As a result, SLCCNV poses a significant threat to cucurbit production if it were to be introduced into an area with large B. tabaci whitefly populations.
SLCCNV has a narrow host range that is limited to species in the Cucurbitaceae family. Although SLCCNV was detected in tomato plants in China, there is no evidence it causes symptoms or is widely found in this solanaceous species (Qiu et al., 2022, Plant Dis. 106).
SLCCNV infects many species of cucurbits and induces a wide range of symptoms, which can be similar to those induced by other begomoviruses, cucurbit-infecting RNA viruses, and nutrient deficiencies. Depending on the host and disease pressure, symptoms appear as early as 8-10 days in newly emerged leaves following infection and often begin as vein clearing and yellowing before progressing into curling, distortion, and mosaic (Figure 1 and 2). The specific symptoms will vary among cucurbit species, but vein clearing and yellowing are often prominent in cucurbits, e.g., yellow vein mosaic disease of pointed gourd (Venkataravanappa et al., 2022, Indian Phytopathol. 75). In many cucurbits infected with SLCCNV, older leaves with vein yellowing senesce early. Plants infected early in development are often severely stunted and have poor fruit set, quality, and yield.
Symptoms of SLCCNV infection may be confused with those caused by the closely related species squash leaf curl Philippines virus (SLCPHV), as well as other begomoviruses, including squash leaf curl Yunnan virus (SLCYNV), tomato leaf curl New Delhi virus (ToLCNDV), squash leaf curl virus (SLCuV), and cucurbit leaf crumple virus (CuLCrV). Of these viruses, only CuLCrV and SLCuV occur in the United States.
SLCCNV is transmitted by species of the Bemisia tabaci whitefly complex, which includes numerous cryptic species, in a persistent, circulative manner, which means whitefly adults can transmit the virus (remain viruliferous) for life. In India, the whitefly (B. tabaci) cryptic species Asia-1 was documented as a vector of SLCCNV (Wu et al., 2020; Venkataravanappa et al., 2021, 2022). In China, SLCCNV is probably transmitted by B. tabaci MEAM1 and MED, which are also prevalent in the Western Hemisphere. The whitefly is a highly efficient vector, and high incidence of disease may occur during months when populations are high (Wu et al., 2020). High rates of transmission (95%) and disease incidence (100%) have also been shown in melon (Wu et al., 2020).
SLCCNV is not transmitted mechanically (via sap). There is also no evidence of seed transmission in squash plants (Venkataravanappa et al., 2021).
SLCCNV was recently reported to occur in mixed infections with SLCPHV (Neoh et al., 2023, Plants. 12). SLCPHV was originally called the SLCCNV strain from the Philippines (Kon et al., 2003, Phytopathol. 151); however, this virus was elevated to species status in 2004 (Mayo, 2005, Arch. Virol. 150). SLCPHV has similar biological properties to SLCCNV but a more limited geographical distribution; SLCPHV has been reported in the Philippines (2003) and Taiwan (2007) (Neoh et al., 2023).
SLCCNV is now widely distributed throughout Asia, including parts of the Middle East.
Note: Years in parentheses indicate when SLCCNV was first officially reported in that location.
For the most up-to-date information on geographical incidence, please visit this website (www.eCucurbitviruses.org) or CAB International’s Invasive Species Compendium
Symptoms alone cannot be used to accurately diagnose SLCCNV infection. Diagnosis requires molecular or serological protocols that are commonly used in many research and diagnostic laboratories.
Currently, molecular tests involving PCR (polymerase chain reaction), RCA (rolling circle amplification), and DNA sequencing are used to identify SLCCHV to strain, i.e., SLCCHV-CN and -IN (Venkataravanappa et al., 2021, 2022; Wu et al., 2020). Other methods of detection, including ELISA (enzyme-linked immunosorbent assay), DIBA (dot immunobinding assay), and IC-PCR (immuno-capture PCR), have been reported and can allow high-throughput testing of field-collected samples (Venkataravanappa et al., 2021). These methods need to be compared and validated.
Contact your local plant diagnostic laboratory to determine testing capabilities.
Visit the diagnostic laboratories page for information on diagnostic laboratories in your state, protocol publications, and/or references describing detection methods for WCLaV-1 and WCLaV-2.
Effective management of SLCCNV requires an integrated pest management (IPM) approach that combines multiple strategies appropriate for the production system and geographical region. SLCCNV-resistant pumpkin varieties are in development at the World Vegetable Center. The AVPU1426 line of squash is resistant to a strain of SLCPHV from Taiwan (Dhillon et al., 2021, Agron. 11). However, there are currently no commercially available SLCCNV-resistant cucurbit varieties.
Therefore, management practices focus on establishment of non-infected plants, suppression of whitefly vector populations, and early detection.
It is vital to avoid introducing SLCCNV or the whitefly vector with transplants into fields or greenhouses. When possible, do not import transplants from areas with a known presence of SLCCNV or other whitefly-transmitted viruses as this can lead to introduction of the virus to new areas. Transplants should be produced in greenhouses, net houses, or protected under row covers. Periodically monitor transplants for SLCCNV symptoms and whiteflies. Systemic insecticides may be applied to reduce whitefly populations on transplants.
The use of row covers, for the first 30 days, to protect young transplants in the field from whiteflies is an effective, though costly, method to prevent early infection of cucurbit plants by SLCCNV and other whitefly-transmitted viruses, especially in areas where whitefly pressure is high (Rojas et al., 2018, Annu. Rev. Phytopathol. 56).
The application of insecticides can be an effective method to manage whitefly populations and slow the spread of begomovirus diseases. Systemic insecticides, such as neonicotinoids and cyazypyr (diamide), can be applied to transplants or plants in the field via drip irrigation or directly to foliage. The application of insecticides to manage whitefly adults and/or nymphs should be implemented with an IPM approach, e.g., based on monitoring whitefly populations with yellow sticky cards (Rojas et al., 2018). Consult local or regional guidelines to determine appropriate materials for suppression of whiteflies and treatment thresholds.
Following harvest, cucurbit plants should be destroyed and removed from the field as soon as possible to eliminate sources of SLCCNV inoculum. Having a cucurbit-free period between harvest and the establishment of the next cucurbit crop or growing season is a sustainable approach that can reduce or delay begomovirus disease pressure (Rojas et al., 2018). Host-free periods are most effective when implemented on a regional basis.
Consult local or regional guidelines for variety recommendations, production practices, and pesticide programs to help maintain cucurbit health, which would make it easier to detect potential virus symptoms.
If you observe plants with suspected virus infections, contact your local plant diagnostic laboratory.
Gilbertson, R. L. and Maliano, M. R. 2017. Yellow vein mosaic. In Keinath, A.P., Wintermantel, W. M., and Zitter, T. A. (eds.), Compendium of Cucurbit Diseases and Pests, 2nd edition (pp. 120). American Phytopathological Society Press.
Visit the References page for a full reference list of cited articles.
This work is a publication of the Emerging Viruses in Cucurbits Working Group (EVCWG). It is supported by funding from the USDA NIFA (Agreement 2018-70006-28884) through the Southern IPM Center’s grant program project S22-026. Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and the EVCWG and do not necessarily reflect the views of the USDA NIFA or the Southern IPM Center.
This publication may be distributed without alteration for nonprofit educational purposes provided that appropriate credit is given to the authors and the Emerging Viruses in Cucurbits Working Group. Permission for any other uses should be requested from the Emerging Viruses in Cucurbits Working Group.
Authors: Eric Hickerson, University of California – Davis, and Robert L. Gilbertson, University of California – Davis.
Senior editors: Rebecca A. Melanson, Mississippi State University, and William M. Wintermantel, USDA-ARS.
Reviewers: Olufemi J. Alabi, Texas A&M University, and Phyllis Himmel, University of California – Davis.
The Emerging Viruses in Cucurbits Working Group and its outreach activities are supported by funding from the Southern IPM Center’s Southern IPM Grants 2022. Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and the Emerging Viruses in Cucurbits Working Group and do not necessarily reflect the view of the Southern IPM Center.
Last updated August 2022 / Privacy
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