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Papaya Ringspot Virus (PRsV)

Papaya (Carica papaya L.) is one of the most widely consumed agricultural commodities by the people of Indonesia. Papaya is a tropical fruit. The origin of this fruit comes from Central America, then spread to various other hemispheres. Papaya productivity is greatly influenced by natural factors, including pest and plant disease disorders. In 2018 many expanse of papaya gardens that failed to harvest due to disease attacks with symptoms such as prominent mosaics on the leaves, chlorosis on the leaf lamina, and lines like oily on the petiole. The fruit of the plant shows rounded patches like 'ring spots' and on severe attacks the thickened and hardened brown spots and fruit are not tasty to eat. Symptoms of this disease may be infected with the papaya ring spot virus (PRsV) which also has the synonym papaya distortion mosaic virus, papaya ringpot distortion virus, papaya leaf distortion virus.

Symptoms of PRSV attack on leaves (A, B, C), on stems (D, E) and fruit (F, G)

The transmission efficiency of PRSV can be through 2 species of aphids namely Aphis gossypii and Myzus persicae (Sulzer). To prevent the spread of the virus, it is necessary to eradicate diseased plants and control vector insects that help spread it.

Sources: Affandi and Tri Budianti
Editor: Web Team

FLOUR DISEASE ON RAMBUTAN

Rambutan fruit has a very high nutritional content, including carbohydrates, protein, fat, phosphorus, potassium, calcium, vitamins B1, B2, B3, B5, B6, B12, folate, manganese, magne-sium, iron and vitamin C. Di in 100 g of rambutan fruit, there are 69 calorie content, 66.75 mg of vitamin C. In addition, it is also reported that the fiber content is also high, which is 2 g per 100 g of fruit, so it is suitable for people who want to lose weight diet.

Rambutan rind contains tannins and saponins, which can be used for drugs of dysentery and fever. Meanwhile, the seeds contain fat and polyphenols which can be used to treat diabetes mellitus or diabetes. Leaf contains tannin and saponin. Bark contains tannins, saponins, flavonoids, pectic acids, and iron and can be made as a mouthwash as a mouth ulcer.

For the last five to ten years rambutan in various regions has been severely affected by powdery mildew. Even this powdery mildew attack has reached epidemic levels. However, until now the quantity is not known with certainty how much loss due to this flour dew disease. What is clear, the appearance of the fruit after ripe is very unattractive because the hairs are short and tend to be bald (Figure 4B and Figure 5).

Cause of disease

This disease was reported for the first time in Indonesia to attack rambutan plants in Bogor and Jakarta by T. Hadiwijaya in 1949. The cause of this disease was the fungus Oidium sp. Because this fungus is thought to only attack rambutan plants, it was given the name O. nephelii nov.sp. Hadiwijaya. This fungus is an obligate parasite, meaning that it cannot be bred on artificial nutrition media. Mushroom O. nephelii nov.sp. Hadiwijaya produces mycelium which only grows on the surface of plant tissue, never attacks the tissue itself. They get nutrients from plants by forming haustoria that enter the epidermal cells of plant organs. On the surface of plants, mycelium produces short-sized conidiophores. Each conidiophore produces an egg-shaped conidia chain that is easily spread by the wind.

Symptoms of the disease.

This fungus mainly attacks vegetative and reproductive parts that are still young and actively growing (shoots, flowers and fruit), while old leaves and fruit are not attacked.

Symptoms of disease in fruit are first shown by the presence of white flour-like grains covering the surface of the flower (Figures 1 A and B), fruit (Figures 2 A and 2 B), shoots, and young leaves (Figure 3). The initial disease infection in the fruit will cause fruit development to be slow, deformed, necrosis and shortened fruit hairs. As a result, the fruit which is attacked by powdery mildew will change its color to brown (Figure 4 A and B).

 

Powdery mildew can attack plants in nurseries throughout the year. This is caused because usually the seedlings in the nurseries are given shade so that the relative humidity ranges from 71-81%. In a laboratory room, mature spores can germinate at high 76-100% when stored for one to three days in a dry container.


Disease spread.
For now, powdery mildew is one of the most prevalent groups of diseases that cause damage to rambutan plants throughout the world such as Sri Lanka, Thailand, Malaysia, the Philippines and Indonesia. Therefore, the US Department of Commerce requires exporters who will export fresh rambutan fruit to America in addition to attaching a phytosanitary certificate must also include an additional declaration stating that the shipment has been inspected and is free of O. Nephelii powder dew.

How to control

Some efforts to control powdery mildew disease can be done by:


a. Technical culture which includes reducing the humidity of gardens and trees by: cutting and removing water branches, old and dead branches, remnants of fruit stalks after harvesting, and also cleaning weeds that grow under and around trees.

b. Chemically, it can be done by spraying the plants when the flowers bloom or when the leaves are germinated with fungicides containing sulfur (contact) or chlorothalonil (contact) or Hexaconazole (systemic) compounds. However, consideration must be given to the costs of spraying fungicides with the sale of rambutans to be obtained as well as the negative impacts on health and the environment.

 Source: Ir. Sahlan

 

The Splicing Technique for Different Sizes

In grafting activities we often face different sizes between the rootstock and the upper stem (entres), of course this requires a separate way to be able to do so that the resulting seed provides a percentage of growth that remains optimal.

The following techniques to connect different sizes between the rootstock and upper stem:

1. The rootstock is bigger than the rootstock

a. The rootstock that has been prepared is cut to the height of the recomencation height of 15-20 cm from the base of the stem
b. Middle part of the rootstock with a depth / length of hemisphere between 1.5 - 2 cm
c. The look on one side of the rootstock that has been divided into the size of the stem
d. Spur-shaped stems with lengths between 1.5 - 2 cm
e. Insert the top stem that has been knotted in the lower half of the stem
f. Make binding on the connection
g. 2 - 3 weeks can see the results of the connection

 

 

2. Rootstock is smaller than the rootstock:

a. The rootstock that has been prepared is cut to the height of the recomencation height of 15-20 cm from the base of the stem
b. Middle part of the rootstock with a depth / length of hemisphere between 1.5 - 2 cm
c. The shape of the stem is spur with a length of between 1.5 - 2 cm and another shape the size of the stem
d. Insert the top stem that has been knotted in the lower half of the stem
e. Make binding on the connection
f. 2 - 3 weeks can see the results of the connection

 

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 Source : Cipto K dan RJ Ali
photos : Masirul