Cucurbit Aphid-Borne Yellows Virus on Cucumber

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» Cucurbit aphid-borne yellows virus (CABYV) is becoming a substantial problem for greenhouse cucumber producers in Europe and the Mediterranean Basin.
» CABYV has been identified in North America, but major epidemics have not yet occurred on greenhouse grown crops.
» Preventing the entry of the aphid vectors into greenhouses is the primary means of managing CABYV on greenhouse cucumbers

The disease cucurbit aphid-borne yellows (CABY) is caused by the Cucurbit aphid-borne yellows virus (CABYV). This virus was first isolated in France in 1988 and, most likely, has been in Asia and the Mediterranean basin for many years.1 CABY occurs commonly in regions including Algeria, France, Greece, Iran, Lebanon, Spain, Tunisia, Turkey, and Sudan.^1,2 Seventy percent of the cucurbits tested in Tunisia between 2000 and 2004 were infected with CABYV, as were eighty-three percent of melons in Spain in 2003 and 2004 and forty-one percent of cucurbits tested in France between 2004 and 2008.2 The pathogen has been detected in North America and Oceania, but occurrences have been infrequent.1 CABYV was reported on greenhousegrown cucumbers in Iran in 2012, in Germany in 2019, and in Belgium and the Netherlands in 2021 where the disease is becoming a major concern for the industry.^3,4,5

The report of CABYV on greenhouse cucumbers in Germany indicated that in most instances, 10 to 50% of the cucumber plants in a house were symptomatic, and in some cases, up to 90% of the plants showed symptoms. When severe, the CABYV infections result in yield reductions of up to 50%.⁴ The incidence of CABYV in greenhouses in the Netherlands was initially relatively low, with only a few symptomatic plants observed in some houses and up to 10% in others.5 However, disease levels have since increased to be similar to those reported in Germany.

CABYV has a fairly wide host range, able to infect most cucurbit species as well as a number of non-cucurbit crop and weed species. Beets, chickpea, faba bean, lettuce, passion fruit, and tomatoes are known hosts of this virus. Weed hosts include velvetleaf, spiny amaranth, shepherd’s purse, wild mustard, common poppy, and black nightshade.1 Beets may have been an important reservoir host for recent epidemics in the Netherlands and Belgium. 

The primary symptom of CABY on cucurbit plants such as cucumber, melon, and squash is the yellowing of older leaves (Figure 1). In some cases, depending on the cultivar, the entire plant can show the yellowing symptom.^1,2,6 Yellow mottling and interveinal chlorosis (veins stay green) also can occur (Figure 2). CABY affected leaves often become thick, leathery, and brittle. Symptoms typically do not develop on the fruit, and CABYV infection does not usually affect fruit quality. CABY induces flower abortion, the primary factor affecting yield, resulting in fewer fruit produced on each plant. The reduced fruit load can result in larger fruit, which may affect marketability if fruit are not harvested at the right time.^1,2,6,7 However, when disease pressure is high, fruit may not develop to the point where they reach the desired market size and may have a reduced shelf-life.

CABY symptoms are similar to symptoms associated with diseases caused by other yellows viruses on cucurbits, including Cucumber yellow stunting disorder virus (CYSDV), Beet pseudo-yellows virus (BPYV), Cucumber vein yellowing virus (CVYV), and Cucurbit chlorotic yellows virus (CCYV), which is why the pathogen may have been in the Mediterranean region for many years without being detected. Co-infection with more than one virus is known to occur, further complicating diagnostic efforts.^8,9

CABY symptoms can also be mistaken for symptoms associated with nutrient problems, including magnesium deficiency.^1,2 To verify that symptoms are the result of CABYV infection, samples of affected leaves should be tested by a plant diagnostic lab. Commercial ELISA tests, which check for the presence of viral proteins, are available, but they can cross-react with some related viruses. RT-PCR tests, which test for the specific nucleic acid (RNA) sequences of CABYV, are more specific and sensitive than the ELISA tests.

CABYV is a phloem-limited virus that is transmitted (vectored) by aphids, mostly by the cotton aphid, Aphis gossypii (Figure 2). The aphid’s stylet (feeding tube) must be inserted into the phloem vascular tissue for the aphid to acquire the virus from an infected plant and later to transmit the virus to a non-infected plant. The aphids must feed on an infected plant for several hours or days before they acquire CABYV. An extended feeding period is also required to transmit the virus. For many other aphid transmitted viruses, only a few seconds or minutes of feeding are required for aphids to acquire or transmit the virus. Other aphid species, including the green peach aphid (Mysus persicae) and the potato aphid (Macrosiphum euphorbiae), are also able to transmit CABYV. However, these species are much less effective than A. gossypii in vectoring CABYV.^1,2,6

CABYV is persistent, circulative, and non-propagative in the aphid, meaning that once an aphid acquires CABYV, the insect will be able to transmit the virus for the rest of its life. The virus circulates through the aphid’s body, eventually accumulating in the salivary glands. It is then injected into the plant’s phloem tissue when the aphid feeds. After an aphid feeds on an infected plant and acquires CABYV, it takes one to three days before the aphid can transmit the virus. CABYV does not multiply in the aphid, and the virus is not passed on to the aphid’s offspring. The virus is not mechanically transmitted (transmitted in infected sap). CABYV spreads throughout the cucumber plant through the phloem tissue. CABY has not been reported to be seed transmitted, and the quality of seed produced on CABYV infected plants is not affected by the disease.^1,2

Higher disease levels and greater impacts on yield occur if younger plants are infected. Disease levels are also dependent on population levels of the aphid vector and the abundance of CABYV in nearby reservoir hosts. Infected weed species and garden or commercial cucurbit crops can serve as sources of CABYV for greenhouse-grown cucumbers.^2,7  

At this point, the options for managing CABYV on greenhouse cucumbers are limited. Managing the availability of inoculum by controlling weed hosts near greenhouses is generally not practical, and because the disease can spread so quickly, it may not be effective in many situations.1 Applying insecticides to prevent or delay transmission by the aphids vectors has also not been shown to be effective in managing CABY, at least in field production systems.^1,2 Resistance to CABYV has been identified in melon, cucumber, squash, and bitter gourd accessions. However, resistance to CABYV is not currently available in commercial cucumber varieties.^1,6

The best option for preventing CABYV infection of greenhouse cucumber crops is to prevent the entry of aphids into the house by using insect exclusion screens or netting. Monitor aphid populations in the greenhouse regularly using yellow sticky cards placed in and around the crop canopy. Some references recommend against destroying or removing CABYV infected plants in the greenhouse with the idea that the process will cause infectious aphids to move to neighboring plants, thus increasing disease spread. The effectiveness of this recommendation has not been verified, and some anecdotal evidence suggests that removing infected plants as soon as they are detected helps slow disease spread and protect yield potential.^4,5

1 Cucurbit aphid-borne yellows virus (Cucurbit aphid-borne yellows). 2021. CABI Invasive Species Compendium. https://www.cabi.org/isc/datasheet/110067.
2 Cucurbit aphid-borne Yellows Virus. 2012. Advances in Virus Research. https://www.sciencedirect.com/topics/agricultural-and-biological-sciences/cucurbit-aphidborne-yellows-virus.
3 Bananej, K., Menzel, W., and Glasa, M. 2015. Current status of Cucurbit aphid-borne yellows virus in some greenhouse and open field cucumber in Iran. Appl. Ent. Phytopath. 82:13-20.
4 Menzel, W., Maeritz, U., and Seigner, L. 2020. First report of Cucurbit aphid-borne yellows virus infecting cucurbits in Germany. New Disease Reports 41, 1. http://dx.doi.org/10.5197/j.2044-0588.2020.041.001.
5 Smith, E. 2021. Growers warn of massive spread of new virus in Dutch cucumber crop. Hortidaily. https://www.hortidaily.com/article/9342121/growers-warn-of-massive-spread-ofnew-virus-in-dutch-cucumber-crop/.
6 Davis, M., Turini, T., Aegerter, B., stapleton, J. 2008. Cucurbit aphid-borne yellows. UC IPM Pest Management Guidelines. UC ANR Publication 3445.
7 Schoeny, A., Rimbaud, L., Gognalons, P., Girardod, G., Millot, P., Norzeran, K., Wipf-Scheibel, C., and Lecoq, H. 2020. Can winged aphid abundance be a predictor of cucurbit aphid-borne yellows virus epidemics in melon crop? Viruses 12(9):911.
8 Papayiannis, L., Ioannou, N., Boubourakas, N., Dovas, C., Katis, N., and Falk, B. 2005. Incidence of viruses infecting cucurbits in Cyprus. Journal of Phytopathology 153Z:530-535.
9 Kwak, H., Byun, H., Choi, H., Han, J., Kim, C., Wintermantel, W., Kim, J., and Kim, M. 2021. First report of cucurbit chlorotic yellows virus infecting cucumber in South Korea. Plant Disease 105. DOI10.1094/PDIS-10-20-2254-PDN.
Websites verified 2-1-2022

For additional agronomic information, please contact your local seed representative.
Performance may vary, from location to location and from year to year, as local growing, soil and weather conditions may vary. Growers should evaluate data from multiple locations and years whenever possible and should consider the impacts of these conditions on the grower’s fields. The recommendations in this article are based upon information obtained from the cited sources and should be used as a quick reference for information about greenhouse cucumber production. The content of this article should not be substituted for the professional opinion of a producer, grower, agronomist, pathologist and similar professional dealing with this specific crop.
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