Question

Tungro disease of rice is caused by
a. Mycoplasma
b. Prions
c. Viroid
d. Virus

Answer 1

Hint: As we know that the Rice tungro disease is widely distributed in South and South-east of the Asian countries and it has been recognized as a serious limitation to the rice production. Earlier this disease was considered a nutritional disorder of rice. Tungro means degenerated growth.

Complete answer:
- “Tungro” is known as degenerated growth and the disease is called as yellow-orange leaf in Thailand. It is majorly observed in India, Thailand, Pakistan, Indonesia, etc.
- Rice tungro bacilliform virus (RTBV) and Rice tungro spherical virus (RTSV) these two viruses were found to be associated with the Rice tungro disease. Here, RTBV is a double stranded (ds) DNA genome virus whereas the RTSV is a single stranded (ss) RNA virus.
- Rice infected with both RTBV and RTSV or by RTBV alone can produce a significant reduction of more than 85% in the yield whereas if they are infected with RTSV alone this much reduction is not seen.
- Its symptoms depend on host cultivar (a plant variety that have been produced in cultivation) seedlings show stunting with yellowing of leaves, reduced tiller(each segment containing its own two part leaf), yellowing of leaves is a very common symptom.
- RTBV ds DNA bacilliform virus which causes mild stunting and yellowing of leaves and RTSV ss RNA virus cause very mild stunting.
- Tungro viruses are transmitted by six leafhoppers species. Virus is transmitted from one plant to another through the mouth of green leafhoppers i.e. when they feed on the diseased plant virus particle gets attached to their mouth part and they fly and feed on another plant , the virus particle from their mouth gets introduced into the healthy plant.
- Insecticides applied to the roots of plants provide the most efficient uptake and also much slower the rate of degradation.

Hence, the correct answer is option (D).

Note: In approximately 7 minutes the leafhoppers can feed and transmit the virus and symptoms can appear. Rice tungro disease has the maximum potential to cause a huge loss in rice production. It is must to remember that RTBV is double stranded DNA bacilliform virus and RTSV is single stranded RNA virus.