The following are recommendations for executing the survey using the approved methods for pest surveillance. The recommendations are developed through literature review and consultation with subject matter experts.
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).