Figure 1: CGMMV symptoms on cucurbit leaf
Guest Article
Authors: Helena Piñar and Carlos Caceres, Nakama SCA, Almeria, Spain.
Cucumber Green Mottle Mosaic Virus (CGMMV)
CGMMV belongs to the Tobamovirus family, like Tomato brown rugose fruit virus (ToBRFV). This tobamovirus, which causes disease in cucurbits, was first detected in the 1990s in cucumber crops in Almería, Spain (Célix et al., 1996). Since then, we have continued to learn about this pathogen that affects various crops, although cucumber is its most vulnerable host.
How does this virus affect crops?
In cucumbers, symptoms are particularly severe. Under ideal conditions, you may observe distorsion on leaves and fruit deformities. Although leaves may show a mild mosaic with slight deformations in watermelons, the most evident damage occurs in the fruit's flesh. In melons, leaves can exhibit chlorosis and mosaic patterns, while in zucchini, infections are often asymptomatic, making it very complicated to detect. CGMMV is an extremely resilient virus that can survive for long periods in soil, tools, and surfaces. It is also transmitted through seeds, water, cultural practices, and even bumblebees, making it a significant challenge for crop management.
A virus with European and Asian roots
CGMMV has two main variants: the European type (detected in France, the Netherlands, Russia, and Uzbekistan) and the Asian type (found in countries like China, Japan, and South Korea). Until 2015, the European type was predominant in Spain. However, recent research (Crespo et al., 2017) has revealed a shift: the Asian type is now overcoming the European type, becoming more common in crops.
What does this mean for farmers?
The coexistence of these two variants in the same plant increases the risk of genetic recombinations, which could generate new virus strains with unknown features. An example of this phenomenon occurred with Tomato yellow leaf curl virus (TYLCV) in tomatoes, which has developed increasingly aggressive variants. The TYLCV isolate found in Almería is a more aggressive recombinant strain.
How do we identify CGMMV variants?
According to research by Crespo et al., 2017, the Asian variant can be identified because it produces local lesions on the leaves of Chenopodium amaranticolor (commonly known as Lambs quarters), something the European variant does not do. Molecular analyses can also differentiate the two. In melons, the behavior of both variants differs. According to L. Ruíz et al., 2021, out 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 Cucumber mosaic virus (CMV).
The “antagonistic” effect of the Asian type
A study by CEBAS-CSIC found that when both the Asian and European variants infect cucumber simultaneously, the presence of the Asian type reduces the accumulation of the European type. This could explain why the Asian type is prevailing in Spanish fields.
CGMMV and ToLCNDV: A duel in zucchini
As described by Crespo et al., 2019, in zucchini, the interaction between CGMMV and Tomato leaf curl New Delhi virus (ToLCNDV) can create an interesting effect: CGMMV seems to “suppress” the typical symptoms of ToLCNDV, including vegetative damage. This may cause a ToLCNDV infection to go unnoticed. For this reason, it is essential to perform specific tests for both viruses in zucchini, even if no apparent symptoms are observed.
How to protect against CGMMV?
To prevent CGMMV infection, it is crucial to use seeds from companies that ensure their seeds are virus-free and to use resistant varieties whenever possible. Additionally, implementing a solid hygiene plan that addresses the following points is vital:
- Disinfection of tools and equipment
- Disinfection of structures and machinery
- Use of single-use gloves, gowns, and shoe covers for visitors
- Proper work attire
- Organized workflow within greenhouses
- Scheduled sampling
Commercial test kit options available from Agdia
Figure 2. Agdia's high-sensitivity CGMMV ImmunoStrip®
A leading provider of diagnostic solutions for agriculture, Agdia, Inc. has been serving plant breeders, propagators, growers, universities, and private testing laboratories since 1981. Agdia offers many diagnostic options for growers and laboratories alike to detect cucurbit pathogens. Options for viruses mentioned in this article include:
- ImmunoStrip® for CGMMV
- ELISA test kits for CGMMV
- ImmunoStrip® for ToLCNDV
- ELISA test kits for ToLCNDV
- Click here for all test kit options for cucurbit pathogens
Conclusion
CGMMV continues being a challenge for farmers. Its persistence and transmission capabilities, together with the emergence of new variants and its interactions with other viruses, highlight the importance of prevention and continuous crop monitoring. Stay alert, conduct regular tests, and maintain good field hygiene to protect your harvests.
ImmunoStrip® is a registered trademark of Agdia, Inc.
