Cucumber; Pumpkin/Squash/Zucchini; Watermelon

No known vector.

No specific signs are present.

Seedlings: "Symptoms may be indistinct or difficult to recognize as being caused by a virus on young seedlings. In severe infections, cotyledons may become yellow, but symptoms are usually not seen until the first or second leaf stage" (ASTA, 2014).

Leaf: Early symptoms include vein clearing (the disappearance of green color in or around leaf veins) and crumpling on young leaves, while mature leaves become bleached and chlorotic (ASTA, 2014; Reingold et al., 2016). Mild to severe leaf distortion can occur with leaf mottling and blistering and plant stunting. Leaf distortion can be more severe at low temperatures when plants grow more slowly. The onset of symptoms after exposure varies according to host, amount of inoculum and environmental conditions. Symptoms in cucumber leaves can appear within 7 to 14 days after infection.

Fruit: Typical symptoms in infected fruit include green mottling, spotting, and streaking (ASTA, 2014; Reingold et al., 2016). Infected fruit, however, do not always show symptoms (ASTA, 2014). In some cases, fruit that show no external symptoms may be internally discolored or necrotic. This seems to be especially pronounced in watermelon (ASTA, 2014; Tesoreiro et al., 2016).

Other symptoms in cucumber: In the early infection, young leaves of infected cucumber plants displayed light green mottle and blisters. The infected plants were stunted in growth, with darker green blisters and green mottle mosaic symptoms on mature leaves (Ling et al., 2014). Root systems in inoculated cucumber seedlings are underdeveloped compared to healthy seedlings (Fletcher, 1969).

Other symptoms in watermelon: In addition to leaf mottling, symptoms include damage to the fruit stalk, necrosis on the fruit peduncle, and underdeveloped fruit (ASTA, 2014; Tesoriero et al., 2016).

Serological: There are several field-based screening aids available for CGMMV surveying. An immunoStrip test is available from Agdia that does not cross react with other known viruses that infect cucurbits ( ISK 45700). Another test kit is available from Hangzhou Keen Biotech Co., Ltd. These tests may be used on suspect symptomatic host material. At least two DAS-ELISA kits are also commercially available for CGMMV detection in symptomatic leaves (LOEWE FAST Kit CGMMV and Agdia ELISA Reagent Set for CGMMV ).

Confirmation requires a combination of molecular techniques and sequencing. Suspect positive samples should be sent to the CPHST Beltsville lab.

Symptoms of CGMMV can be confused with those caused by many other cucurbit viruses, making diagnosis based exclusively on visual symptoms unreliable (ASTA, 2014). Mixed infections with other viruses are common. In a study in the Middle East, several other viruses were found in squash and watermelon fields which contained CGMMV including: Arabis mosaic virus (ArMV), Cucumber Mosaic virus (CMV), Squash leaf curl virus (SLCV), Squash mosaic virus (SqMV), Watermelon mosaic virus (WMV), and Zucchini yellow mosaic virus (ZYMV) (Al-Tamimi et al., 2009). Mixed infections containing CGMMV and Melon necrotic spot virus (MNSV) were reported in cucumber in Canada (Ling et al., 2014). Melons infected with CGMMV in California were also found to be infected with SqMV (Tian et al., 2014). Molecular confirmation is necessary to identify CGMMV.

There are many published molecular diagnostic methods which can detect CGMMV. For example, the virus can be detected by conventional RT-PCR, and primers using the highly conserved regions of CGMMV movement protein (MP) and coat protein (CP) can detect different strains of the virus. Numerous different sets of primers have been designed for CGMMV detection by RT-PCR (Boubourakas et al. 2004; Ling et al., 2014; Reingold et al., 2015).

Li et al. (2013) developed a one-step reverse transcription loop-mediated isothermal amplification (RT-LAMP) for the detection of CGMMV in watermelon plants or seeds.

Shang et al. (2011) describe five serological methods for detection of CGMMV, including: Antigen-coated plate enzyme-linked immunosorbent assay (ACP-ELISA), triple antibody sandwich enzyme-linked immunosorbent assay (TAS-ELISA), Dot-immunobinding assay (DBIA), direct tissue blot immunoassay (DTBIA), and immunocapture reverse transcriptase polymerase chain reaction (IC-RT-PCR).