Rice tungro disease is caused by the combination of two viruses, which are transmitted by leafhoppers. It causes leaf discoloration, stunted growth, reduced tiller numbers and sterile or partly filled grains.
Tungro infects cultivated rice, some wild rice relatives and other grassy weeds commonly found in rice paddies.
Symptoms
In ricefields that are affected with tungro, plants are infected with either both RTBV and RTSV, or with each virus alone. Doubly infected plants show typical so-called 'tungro symptoms', including plant stunting, yellow or orange discoloration of leaves, and reduced tiller number. The discoloration starts from the leaf tip and extends to the lower part. Discoloured leaves may have irregular, small, dark-brown blotches. Younger plants may show interveinal chlorosis. Plants infected with RTBV alone show milder symptoms; plants infected with RTSV alone show very mild stunting but no yellowing of the leaves.
Causal organism
Rice tungro is a composite disease caused by two viruses, i. e Rice Tungro spherical Virus (RTSV). RTSV is a spherical single stranded RNA virus 30-33nm in size. This virus cause very mild stunting without leaf symptom. Rice Tungro Bacilliform Virus (RTBV) is bacilliform, double stranded DNA virus. RTBV causes the main symptom and the RTSV intensify the symptoms RTBV depends on RTSV for transmission by insect vector.
Disease cycle and Transmission
The viruses survive in wild host like leersa, Echinochloa etc. It is transmitted by green leaf Hopper (GLH) insect vector like Nephotettix virescens , Nephotettix nigropictus ,nephotettx apicalis Racilia,etc . in a semi persistent manner. Out of these Nephotettix virescens is the most efficient vector.
