Biology and symptoms of cucumber green mottle mosaic virus (CGMMV)

Read about how the CGMMV develops and what symptoms to look out for.

Cucumber green mottle mosaic virus (CGMMV) is a tobamovirus and occurs as a number of strains across the world, with at least two of these being present in the UK.

The infection is localized, to begin with, but may spread via the vascular system into a systemic infection.

The exact mechanism that the virus uses to move throughout the plant is unknown.

Virus particles are found throughout the plant and can even be found in small quantities in pollen.

Leaf symptoms

Leaf symptoms of the type strain are quite easy to identify. They produce a characteristic dark/light green mottled appearance on the youngest leaves, although severity may vary with cultivar.

Light areas are flattened in appearance, and the dark areas raised.

Symptoms disappear as the foliage ages, and there are usually no symptoms on the fruit, although some strains do produce fruit symptoms.

Early symptoms of cucumber green mottle mosaic virus starting to show in the head of cucumber plant

Image © Tim O’Neill (ADAS).

Dark patches and leaf blisters caused by cucumber green mottle mosaic virus

Image courtesy of Derek Hargreaves.

Patch and blister symptoms of cucumber green mottle mosaic virus which become less clear as they leaves expand

Image © Tim O’Neill (ADAS).

When CGMMV infection occurs on young plants in the replanting period (i.e. at higher light levels), infected plants can sometimes wilt.

This can be confused with Pythium infection, but in the case of virus infection, the roots are healthy and wilting may only occur in the middle of the plant, with the highest and lowest leaves being less affected.

Occasionally, lighter leaf mottling occurs. This pale strain is still CGMMV but is thought to be the Aucuba strain or a similar yet-to-be-identified strain.

Pale pattern of mottling spreads across leaves as virus spreads

Image courtesy of Derek Hargreaves.

The pale strain does not appear to spread as fast as the type strain, but it still reduces yield.

Its symptoms stay visible as the leaves expand – an attribute that is not shared by the type strain.

Most fruit is unaffected and can be marketed as normal. Still, there are occasional problems with fruit symptoms that may be caused by combinations with other viruses or by the presence of different strains of CGMMV.

Original author: Derek Hargreaves