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Papaya Ringspot virus

 

Papaya Ringspot is one of the diseases more destructive, which appear on the papaya growing worldwide. This type of disease can cause production losses between 5% even 100% depending on the age in which the plant is affected.

This disease is caused by papaya ringspot virus, which belongs to a group of potyvirus. It is not transmitted by seeds, but it is transmitted from infected plants to healthy ones by aphid insects such as Myzus persicae, Aphis gossypii, A, neeri, A. citricola and A. Spiraecola.

This virus is transmitted in a non-persistent way, it means this virus does not need a period of incubation to be transmitted. Once it is caught by the insect, it can be inoculated immediately.

There are two kinds of this virus: Papaya Ringspot virus-P and Papaya Ringspot virus-W. The first attacks not only papaya plantings but also cucurbitaceous plantings (pumpkins, muskmelons, cucumbers among others). The second virus only attacks cucurbitaceous plants.

First symptoms of this disease are variable. Normally, top leaves begin to have a yellow mosaic in the leaf blade and green oily streaks appear on the stem and petiole of younger leaves. These ringspots appear on flowers and fruits and they can be seen even if leaves have no symptoms. Leaves usually have a filamentous appearance known as mano de chango (monkey hand), which is caused by an extreme reduction of the leaf blade. Other symptoms can be the presence of yellow leaves while the rest is green.

As this disease goes on progressively, the growth of leaves and plant decreases, but also some protuberances appear on fruits (abnormal growth). A decrease of yields and brix degrees is very notorious in comparison with healthy fruits.

All age plants are oversensitive to it, but very young plants which are infected, they never produce fruits. However, they do not die.

Globally, symptoms begin to appear 2 or 3 weeks after the inoculation. It is important to stress that temperatures below 20° help the growth of this virus.

Control Measures

On account of the fact that there are no chemical products to eliminate this virus and it is not transmitted by seeds, some measures should be taken to prevent this virus and other insects, such as:

• The infection of an orchard decreases as the distances among infected orchards increases. Therefore, it is recommended to sow plants to 1500 meters from those infected orchards.
• It is also advisable to sow plants far from vegetable crops, especially cucurbitaceous and solanaceous plantings.
• At the tree nursery, plantlets should be protected by meshes. The tree nursery should not be close to other papaya or vegetable orchards.
• It is important to know when the population of vector insects is at its peak to program transplanting when the populating fluctuation is low. It will allow to reduce risks of infections during the very first stage of growing.
• To avoid interval growing, one must not begin new plants alongside growing in production.
• To eliminate uncultivated papaya plants or isolated papaya plants which are located in surrounding areas (within a minimal 1.5-2 kilometer radius)
• Two thousands five hundreds plants must be grown per hectare. However plants having symptoms of diseases must be eliminated to prevent infections. When time of crop has come, two thousands plants are acceptable to get good yields.
• Guard rails should be installed. Some hibiscus flower should be planted around the orchard because its coloration is repels insects. Or fodder sorghum should be planted because it is more attractive to vector insects than papaya plantings. These guard rails can be treated with some systematic insecticide to prevent aphids.
• It is important to eliminate plants having symptoms as soon as they appear. The elimination of infected plants must be a daily work to avoid the propagation of diseases in all growing.
• To establish yellow traps (1.0 x 0.50 meter plastic sheets) covered by a light grease coating or agricultural glue in both sides. Traps' height should be slightly higher than plants. Traps must be separated between 10 to 15 meters and every 3 or 4 rows.
• Weeds must be eliminated all over the orchard and its surrounding areas, because they can house insects.
• One to two percentage mineral oil applications must be done 8-15 days. These oils kill pests, larvae, and eggs among others.

If these measures are taken, growers can control pests and virus. Therefore, the crop may have acceptable yields.

 

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