Key facts about the CGMMV:
The cucumber green mottle mosaic virus (CGMMV) belongs to the tobamovirus family, as does the rough virus (ToBRFV). This tobamovirus, which causes disease in cucurbits, was first detected in the 1990s in cucumber crops in Almería (Célix et al., 1996). Since then, we have continued to learn about this pathogen, which affects several crops, although its most vulnerable host is the cucumber.
How does this virus affect crops?
In cucumbers, the symptoms are particularly severe. Under ideal conditions, we may see bulging leaves and fruit deformities. In watermelons, although the leaves may show a slight mosaic pattern with minor deformities, the most obvious damage occurs in the flesh of the fruit. In melons, the leaves may exhibit chlorosis and mosaic patterns, while in zucchini, the infection is usually asymptomatic, which can complicate its detection.
CGMMV is an extremely resistant virus that can survive for long periods in soil, tools, and surfaces, as well as being transmitted by seed, water, contact during cultivation, and bumblebees. This makes it a significant challenge for crop management.
A virus with European and Asian roots
The CGMMV has two major variants: the European (detected in France, the Netherlands, Russia, and Uzbekistan) and the Asian (found in countries such as China, Japan, and South Korea). Until 2015, the European type predominated in Spain, but recent research (Crespo et al., 2017) has shown a change: the Asian type is displacing the European type and is now the most common in crops.
What does this mean for farmers?
The coexistence of these two variants in the same plant increases the risk of genetic recombination, which could generate new strains of the virus with unknown characteristics. An example of this phenomenon occurred with the tomato yellow leaf curl virus (TYLCV) in tomatoes, which developed and continues to develop more aggressive variants, such that the tomato yellow leaf curl virus now found in Almería is a more aggressive recombinant.
How to identify CGMMV variants?
According to research conducted by Crespo et al., 2017, the Asian variant can be recognized because it causes local lesions on the leaves of Chenopodium amaranticolor, commonly known as red goosefoot, something that the European variant does not do. It is also possible to differentiate between them through molecular analysis.
In melons, the behavior of both variants is different. According to L. Ruíz et al., 2021, of 47 melon varieties analyzed, the Asian variant infected 46, while the European variant infected only 30. However, a Japanese variety called Freeman’s cucumber showed resistance to both variants, as well as to the cucumber mosaic virus (CMV).
The “antagonistic” effect of the Asian type
A study by CEBAS-CSIC found that when the Asian and European variants simultaneously infect cucumbers, the presence of the Asian type reduces the accumulation of the European type. This could explain why the Asian type is becoming prevalent in Spanish fields.
CGMMV and ToLCNDV: a battle in the zucchini
As described by Crespo et al., 2019, in zucchini, the interaction between CGMMV and ToLCNDV (tomato yellow leaf curl virus) can produce an interesting effect: CGMMV appears to “suppress” the typical symptoms of ToLCNDV, including vegetative damage. This can cause a ToLCNDV infection to go unnoticed.
For this reason, it is essential to perform specific analyses for both viruses in zucchini, even if no apparent symptoms are observed.
How can you protect yourself from CGMMV?
It is worth remembering that to avoid infection with CGMMV, it is important to use seeds from companies that guarantee that their seeds are virus-free and to use resistant varieties whenever possible. Similarly, it is very important to implement a good hygiene plan that addresses the following points:
Disinfection of materials and tools
Disinfection of structures and machinery
Use of single-use gloves, gowns, and booties for visitors
Appropriate clothing
Organized way of working inside the greenhouse
Scheduled sampling
Conclusion
CGMMV continues to pose a challenge for farmers. Its persistence and transmission capacity, coupled with the emergence of new variants and its interactions with other viruses, underscore the importance of prevention and continuous monitoring in crops. Stay alert, perform regular analyses, and ensure good field hygiene to protect your crops.