The spread of rice tungro disease can be checked indirectly by controlling the vector by suitable pesticide application. As the plants are more vulnerable to RTV infection during early stages of growth, chemical protection of the nursery effectively reduces green leafhopper population and thereby minimises the build up of virus inoculum as well as the pace of transmission.

Nursery Protection

Tungro virus can not be directly controlled by applying any chemical. The best method of preventing tungro is to grow resistant varieties. A variety may be resistant to virus or the insect vector or to both virus and insect vector.
VIKRAMARYA, developed at Directorate of Rice Research, Hyderabad is the resistant variety now available for general cultivation. Other promising resistant medium duration cultures include: IET 9994, IET 8560 and IET 8565 with slender grains and IET 8902 with long bold grains.

When young (nymphs) and adult green leafhoppers feed on diseased plants, virus particles get attached to mouth parts (stylets). As these insects fly and feed on other plants, the virus particles from the stylets get introduced into healthy plants. The insects pick up virus particles within 5 minutes of feeding and can transmit these particles to other healthy plants. The green leafhoppers can not retain virus for a long time. They acquire virus again through repeated feedings. Generally, 8 -10 days after such an introduction of virus in plants, tungro virus disease symptoms appear.

RTV can appear at any time on rice right from seedling stage. The extent of crop damage and yield loss depends on the growth stage at the time of RTV infection.

Rice Tungro Virus (RTV) is a destructive disease of rice. Incidence of RTV in India was first observed at West Bengal in 1966 and two years later, appeared extensively in eastern Uttar Pradesh and northern Bihar inflicting heavy crop losses. Subsequently, RTV has been observed occasionally in parts of Andhra Pradesh, Assam, Bihar, Kerala, Pondichery, Tamil Nadu, Uttar Pradesh and West Bengal. In Andhra Pradesh, incidence of RTV has been recorded often at low to moderate severity since 1976.

Introduction:

The Chlorotic streak disease was first reported from Cuttack, India in 1978 (Anjaneyulu et al.,1980)

1. Stunting, striping or mottling of newly emerging leaves and Chlorotic streaking,

2. The spikelets get discolored and become sterile

Symptoms of Chlorotic Streak Disease

The symptoms of Chlorotic streak are:

1. Stunting, striping or mottling of newly emerging leaves and Chlorotic streaking.

2. The spikelets get discolored and become sterile.

Transmission of Rice yellow mottle virus

1. Transmissible by chrysomelid beetles belonging to the subfamilies Criocerinae, Cryptocephalinae, Galerucinae (Sesselia pusilla), Halticinae (Chaetocnema spp.) and Hispinae (Trichispa sericea).

2. The long-horned grasshopper Conocephalus merumontanus also transmits the virus (Bakker, 1974).

3. Chaetocnema pulla carries the virus in the field.

4. S. pusilla, C. pulla and T. sericea sometimes acquire the virus in 15 min and also sometimes inoculate in 15 min.

Rice Yellow Mottle Virus (RYMV)

1. The morphology of Rice yellow mottle virus

2. The virus is stable in vitro and easy to purify (Bakker, 1970, 1974). Fresh or deep-frozen young rice leaves, harvested 10-12 days after infection are best for purification.

3. Homogenize small pieces in 0.1 M phosphate buffer pH 5.0 + 0.2% 2-mercaptoethanol (1 g of leaves/20 ml of buffer). Squeeze through cloth. Emulsify extract with 0.5 vol chloroform (5 min) and centrifuge at low speed.

Introduction to Rice Yellow Mottle

1. Rice yellow mottle virus was reported first in Kenya.

2. This disease is also reported from Liberia, Sierra leone and Tanzania.

3. Infection even at a late stage of growth results in significant yield loss and in severe cases the effected plant may die.

Symptoms of Rice Yellow Mottle

1. The virus causes a yellow or orange leaf discoloration, stunting and sterility in rice.

2. Infected rice plants are found first near the bunds but soon thereafter whole fields may be affected.

Cultural methods control of Rice Ragged Stunt

1. Cultural practices for the control of Rice ragged stunt of viral disease. There are no specific cultural methods to control the ragged virus disease except for the use of resistant varieties.

2. Some rice varieties are resistant to the Brown planthopper, to the virus, and to both.

3. Cultivars resistant to the vector have low disease incidence.

4. The application of insecticides to migratory planthoppers is being used in temperate countries to reduce disease incidence.

Host-Plant Resistance of Rice ragged stunt

1. Rice ragged stunt virus (RRSV) is an important pathogen affecting rice cultivation in South and South East Asia.

2. Sequences from the coding region of RRSV genome segments 7 and 10 (non-structural genes), and 5, 8 and 9 (structural genes) were placed in sense or antisense orientation behind the plant expression promoters CaMV35S, RolC, Ubil, Actl and RBTV.

Symptoms of Rice Ragged Stunt

1. Symptoms of Rice Ragged Stunt viral disease.

2. Infected plants become severely stunted during early growth stages of the crop. Leaves become short and dark green with serrated edges.

3. Leaf blades become twisted at the apex or base, which result in the spiral shape of the leaves. Leaf edges turn uneven and the twisting gives the leaves a ragged appearance.

4. Ragged portions of the leaves are yellow to yellow-brown in color. Vein swellings develop on the leaf blades and sheaths.

Rice Ragged Stunt Introduction:

1. Rice ragged stunt disease was first found in Indonesia in 1976 and later had a widespread occurrence in countries throughout Asia where rice is grown.

2. The disease is caused by rice ragged stunt virus and transmitted by the Brown plant hopper Nilaparvatha lugens Stal in a persistent manner.

Predisposing factors of Rice Ragged Stunt

Symptoms of dwarf disease

1. Stunting of the plant and presence of chlorotic or whitish specks on the leaves.

2. The specks may also see on the leaf sheath. Sometimes diffused yellowing is also observed on the distal parts and along the margins of the infected older leaves.

3. Infected older leaves produce diminutive tillers.

4. Number of tillers get reduced when the infection occur in the initial stages.

5. Root growth is also reduced and roots extend horizontally.

Dwarf disease Introduction:

1. In 1983 the dwarf disease was first reported from Japan.

2. The leaf hopper will transmit the disease.

3. The transmition of the virus was reported through the eggs of the vectors.

4. This disease is known to occur in most parts of Japan, Korea and China.

Predisposing factors of Dwarf Disease

Factors favoring the development of Dwarf disease of Rice

Symptoms of Rice Bunchy Stunt disease

1. Rice bunchy stunt virus (RBSV), causes increased tillering and excessive branching, short narrow leaves.

2. In case of severe infestation, branches are formed from upper nodes and leaves are produced in branches.

Predisposing factors of Rice Bunchy Stunt disease

Factors that favor the development of Rice Bunchy Stunt virus disease

1. Late planted rice with more grassy weeds.

2. Presence of ratooned Rice crop

3. Presence of vector

Rice Bunchy Stunt

1. Rice Bunchy Stunt disease was first reported in Fujian, China in 1978. It has been reported in Fujian, Guandong, Guanxi, Hubei, Human, Jaingxi and China.

2. Rice Bunchy Stunt virus particles are polyhydral about 60.3nm in diameter.

3. Rice Bunchy Stunt virus can be purified from infected rice leaves by maceration in phosphate buffer.

4. Purified virus suspension shows maximum adsorption at 260nm and minimum at 240nm.

Rice Bunchy Stunt Virus

Control measures of Rice Grassy Stunt disease

Rice Grassy Stunt virus disease control measures include

• cultural methods and
• use of resistant varieties

Host-Plant Resistance of Rice Grassy Stunt disease

1. The grassy stunt virus is transmitted by the Brown Planthopper Nilaparvata lugens Stal.

2. Disease can also be transmitted by Nilaparvata bakeri Muir and N. muiri China.

3. The interaction between the virus and its vector is persistent without transovarial passage.

Rice Grassy Stunt

1. Rice Grassy Stunt disease described by Rivera et al. (1966) and Bergonia et al. (1966). Virus characterized by Hibino et al. (1985).

2. Synonym for this virus is "Rice rosette virus" (Bergonia et al., 1966).

3. A virus with filamentous particles, many of them circular, with a modal contour length of 950-1350 x 6-8 nm.

Chemical Control of Rice Tungro Disease

1. Incorporate Carbofuran 3 G @ 30 to 35 kg/ ha or Phorate 10 G @12 to 15 kg / ha of nursery in top 2-5 cm layer of the soil before sowing sprouted seeds. If such incorporation is not possible, broadcast the recommended insecticides 4 to 5 days after sowing in a thin film of water and allow this water to seep completely.