V10
General
Pepino mosaic virus (PepMV) is a single-stranded RNA-virus (Potexvirus genus, Fexiviridae family) that was originally isolated from pepino (Solanum muricatum), a South American melon-like fruit. From the season 1999-2000 the virus started to damage greenhouse tomato crops in Europe. Although the virus only causes major problems in tomato cultivation, other plants of the Solanaceae family (night shade family) such as eggplant, black nightshade, some potato and pepper varieties and some plants belonging to the genera Nicotiana (e.g. tobacco), Datura (e.g. thorn apple) and Physalis (e.g. Physalis floridana) can also act as a host.
Life cycle of PepMV
PepMV is primarily transmitted mechanically through plant-to-plant contact, contaminated tools, hands, and clothing. It can also be transmitted via seeds, although this is less common. Once the virus enters a plant, typically through damaged epidermal tissue, it begins to replicate. Inside the host cells, the viral RNA is copied and integrated into the host genome. This process involves the synthesis of viral proteins and the assembly of new virus particles.
Four different strains of the virus are known: the Chilean strain (CH2), the European strain (EU), the Peruvian strain (LP) and the American strain (US1). Within these strains, many different individuals, called isolates, can be observed. In Europe, the Chilean strain (CH2) is dominant and present in 90% of the infections. If more strains are found in case of infection, the infection is usually more aggressive than when only one single strain is present. Within the strains, however, there is also variability among different isolates belonging to the same strain. Although different isolates within one and the same strain are genetically very similar, they can show very different levels of aggressiveness in the plant and, as a consequence, in the severity of the symptoms and the damage they cause. For example, there are very aggressive Chilean isolates, but also very mild ones that cause less symptoms.
Pepino mosaic virus is highly infectious and spreads via infected equipment such as carts, scissors and knives. If plant sap of an infected plant is transferred to a non-infected plant, the non-infected plant is also at risk of becoming diseased. This can also occur when objects such as clothing or telephones have been in contact with infected crops. If one plant in a greenhouse contracts PepMV, the rest of the plants are sure to follow. PepMV can survive in plant debris and on contaminated surfaces for several weeks, remaining infectious and ready to infect new plants.
Damage symptoms
The impact of a PepMV infection for the tomato grower is variable. Several factors contribute to this variability. The genetic identity of the virus – which isolate of which strain – that causes the infection is one them. The moment in the crop cycle when the infection takes place is another factor that might have an important impact on the damage that is caused. For instance, an infection early in the season, when the plant does not yet bear fruit, will typically cause less losses than when the infection takes place when the plants are heavily laden. Typical of the damage caused by PepMV is, that it is very intense for a few weeks and then disappears to eventually return later in the season. This means that damage can be more severe during a certain period of the year, with 50-60% non-marketable fruits.
Moreover, some tomato varieties are more susceptible to quality losses due to PepMV than others and climate also has an impact. In general, when a plant has more stress for whatever reason, losses will be much higher.
Symptoms typically appear 2-3 weeks after infection and can significantly impact the yield and quality of crops like tomatoes.
Typical symptoms are:
Leaves & stems
- Nettle-like heads and/or bubbling of the leaves
- Stunted leaf growth
- Leaves have a pale or grey colour
- Necrotic and dying leaves
- Yellow (chlorotic) and brown (necrotic) mosaic pattern on the leaves
- Yellow spots on older leaves and interveinal chlorosis
- Necrosis of the stems
Fruit
- Yellow or orange mottling on the tomatoes
- Flame-like pattern on the tomatoes
- Cracks and damage to the fruit (splitting open)
Symptoms on fruits can appear with or without symptoms on the rest of the plant, depending on the tomato variety, environmental conditions and PepMV isolate.
How to control Pepino mosaic virus
How to prevent Pepino mosaic virus
Pepino mosaic virus is highly infectious and mechanically transmitted. Possible ways of mechanical transmission are tools, employees, visitors, mobile phones, insects, etc. In other words, all means by which plant sap of an infected plant gets in contact with a non-infected plant. As soon as one single plant in the greenhouse has been infected by the virus, it is impossible to protect the other greenhouse plants from infection because of the rapid spread of the virus. Strict hygiene protocols to prevent entry into the greenhouse are therefore essential.
The most effective way to prevent symptoms of PepMV is cross protection. With this technology, the plants are purposely inoculated with a mild isolate of the PepMV. This prevents subsequent infections with aggressive isolates of the same virus and, therefore, the symptoms of the disease do not develop and there are no yield or quality losses.