Papaya stem, leaf and fruit are affected by ring spot disease. Bangladesh, India, Taiwan, China, Thailand, Caribbean Islands, South America, Florida, Hawaiian Islands, Texas and Philippines have high prevalence of this disease. In 1949, plant pathologist Jenson named the disease ring spot. Dr. Siddiq Publications
Causes of papaya ring spot disease
Papaya ring spot disease is caused by a virus called Papaya Ring Spot Virus-Type P (PRSV-P). It is an RNA virus. This virus is rod-shaped, unenveloped, 760-800 nanometers long and 12 nanometers wide. This virus causes mosaic disease in cucurbits.
Infection of papaya ring spot disease
Papaya ring spot virus is transmitted by whitefly (Myzus persicae) and jab beetle (Aphis gossypii). The virus infects the insect’s body within 15 seconds after the jab beetle feeds on a diseased plant. The insect becomes infected when it comes in contact with healthy plants. If the plant is dense, the disease spreads very quickly.
Symptoms of papaya ring spot disease
1. Stem disease symptoms
(i) The symptoms of the disease appear within 30-40 weeks
(ii) Diseased plants are stunted.
(iii) Dark green scaly spots appear on the stem.
(iv) Growth is stunted when young plants become diseased.
(v) Cracks are seen in the tree when disease incidence is high.
(vi) In the extreme stage of the disease the plant rots and dies.
2. Leaf disease symptoms
(i) Disease symptoms first appear on relatively young leaves.
(ii) Chlorosis occurs in leaves. The leaves are yellow in color.
(iii) Leaves are shriveled, small and deformed.
(iv) Diseased leaves show a greenish-yellow pattern.
(v) Round water-soaked spots are seen at the base of petioles.
(vi) Ring spots and distortion ring spots (mosaic) are seen on leaves.
(vii) Volume of diseased leaves decreases.
(viii) If the attack is severe, some small, deformed leaves can be observed on the plant head. Sometimes leaves have only veins.
3. As a result, the symptoms of the disease
(i) Resulting in circular spots or rings of dark green colour.
(ii) Water-soaked spherical spots form on the fruit and the space between the spots becomes hard.
(iii) Swollen areas are seen in diseased fruits.
(iv) When the fruit matures or turns yellow, the spots become indistinct.
(v) Sweetness and papain decrease in papaya.
(vi) Diseased fruits become smaller and drop off.
(vii) Young plants never bear fruit if diseased.
(viii) The tree does not bear fruit and the yield is reduced by 90%.
Cure/Control of Papaya Ring Spot Disease
1. Diseased trees should be removed and buried or burned.
2. Pesticides should be used on diseased land.
3. Cover the entire land with netting to prevent Aphids.
4. To kill aphids, pesticides like Ragor, Roxin, Perfection 40 EC, Metasystox 25 EC etc. should be sprayed.
5. Regular spraying of pesticides from the beginning of planting prevents disease spread by aphids.
6. Pruning of diseased plants should be stopped. Because the virus can spread from the cut.
7. Jab beetle population must be controlled.
8. Other species should be planted around the papaya plantation and between the rows of trees. It will reduce the infection.
Prevention of papaya ring spot disease
1. Healthy, vigorous and disease free varieties should be used as seeds.
2. Aphids must use nets to prevent insects.
3. Papaya cultivation should be stopped in diseased areas.
4. In the process of cross protection, a weak strain of the virus should be introduced into the papaya plant to make it resistant to the disease. Dr. Siddique Publications
5. Transgenic papaya varieties should be cultivated. Tunsgenic papayas are Rainbow, Sunup etc.
6. New seedlings should not be planted around or within diseased gardens.
7. Mixed farming system should be introduced. Dr. Siddiq Publications
8. Quarantine procedures should be adopted.