Management of Pepino Mosaic Virus in Greenhouse Tomatoes
Table of Contents
Pepino mosaic virus (PepMV) was first found in Peru in 1974 on pepino (Solanum muricatum), an edible fruit known as pear melon. In 1999, the disease was found for the first time outside of South America, in greenhouse tomato crops in the Netherlands. Subsequently, its incidence in greenhouse tomato crops was reported in several other European countries and in North America. However, tests have shown that the PepMV discovered in Europe is different from the original PepMV reported in Peru which does not show symptoms on tomato.
To date, the only known naturally occurring host of the European isolate of PepMV is tomato. Infection of other solanaceous crops such as eggplant, tobacco, and potato has only occurred through artificial inoculation studies. Inoculation tests in the UK produced mosaic symptoms on leaves of the potato varieties, Maris Peer, Pentland Dell, and Charlotte. Infection of other solanaceous species including pepper has not yet been demonstrated. Similar tests have shown that cucumbers can be artificially infected but the disease does not appear to spread systemically in the plant.
Experience in The Netherlands indicate that symptoms are more readily seen during the fall and winter months when light levels and temperatures are lower. During the warmer, brighter months, older plants may harbour the virus but not show any symptoms. Symptoms usually appear 2-3 weeks after infection and tend to spread along the row. Affected plants often show stunting of the 'head' (Figure 1), or damage resembling hormonal herbicide damage (Figure 2). Leaves around the 'head' may show dark spots (Figure 3) while lower leaves may have brown, necrotic lesions (Figures 4, 5) that can resemble damage caused by water that dripped onto the plant (Figure 6). Other leaf symptoms may consist of a yellow spot or spots (Figure 7) which later develop into bright yellow patches on the leaf (Figures 8, 9). Stems can have brown streaks (Figure 10) that may encircle the entire stem close to the growing point, as well as the stems of the flowering clusters (Figure 11). Such browning can affect the developing flowers, causing them to abort (Figure 12). The calyx of affected developing fruits can also appear brown (Figure 13).
However, as indicated earlier, infected leaves and fruits may not show any symptoms. Also, symptoms may be observed on a few fruit clusters or leaves, and then not appear subsequently. Symptoms observed on infected fruits have been described as 'marbled' and may be more readily seen in red beef varieties. There is no clear information on how PepMV affects fruit quality. Different symptoms are exhibited among different tomato varieties and there has been no correlation between variety and susceptibility to the virus.
Figure 1. Stunted growth of "head" or growing point of tomato plant.
Figure 2. Distorted growth resembling hormonal herbicidal damage.
Figure 3. Dark spots on young leaves close to growing point.
Figure 4. Necrotic spots on lower leaves.
Figure 5. Spots resembling scorched areas on lower leaves.
Figure 6. Damage resembling damage from water dripping onto plant.
Figure 7. Bright yellow spot on leaf.
Figure 8. Increased numbers of yellow spots on lower leaves.
Figure 9. Bright yellow patches on fully expanded leaves.
Figure 10. Brown corky streaks on leaf stem.
Figure 11. Browning of flowering sets and stem close to growing point.
Figure 12. Browning and abortion of flowers.
Figure 13. Partial browning of calyx of developing fruits.
PepMV is a very contagious disease easily spread mechanically via contaminated tools, shoes, clothing, hands, and plant-to-plant contact. Crop workers can transmit the virus simply by brushing against affected plants. Scientists in the UK have found the virus in the roots of plants, and Dutch workers have infected plants with contaminated leachate. The virus is thought to remain viable in dry plant material for as long as 3 months. At 18°C -21°C, the virus can remain infected for greater than 90 days. Clothing worn in an infected crop is reported to remain infectious for at least 14 days. In moist organic debris held at 10°C, the virus remains stable and considered capable of infection for a relatively long period.
Tests using a high density of bumblebees have been associated with spread of PepMV in a crop. However, the risk of spreading the virus via hand pollination may be greater. The virus can be transmitted by grafting or taking suckers from mother plants. For spread of the virus over long distances, several possibilities exist and these include the sap in fruits and contaminated seed material. Although the original Peruvian PepMV is not seed-borne, experience in Europe suggests the virus may be transmitted by seed at a very low rate, or possibly as a contaminant on seeds. Further investigation into these and other methods of spread of this disease is required.
It is important to prevent the introduction of the disease by using disease-free seed and plant material. To minimize introduction, spread, and carryover of PepMV, strict hygiene at all stages during crop production, and a thorough cleanup procedure between crops, are essential.
During Crop Production
Monitoring of Crops
Regular monitoring and close checking of the crop for symptoms is absolutely necessary for early detection of disease and increased chances of eradication. Take all suspect plants immediately to be diagnosed by an expert.
Steps to take at first detection of disease
Crates, Carts & Packing
Between Crop Cleanup
Tools and Equipment
To make a 1 or 10% TSP solution
First make a stock saturated solution by dissolving approximately 250 g TSP in 1 litre of water and keep tightly sealed to avoid absorption of carbon dioxide. This solution is very alkaline with a pH of about 12. For a 1% solution, mix one part of the saturated solution to 99 parts of water, and for a 10% solution, mix one part of the saturated solution to 9 parts of water.
To make a 0.5% sodium hypochlorite solution
Mix one part of household bleach to 9 parts water.
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