New virus behind mystery dwarfing of rice

THE INDIAN Agricultural Research Institute (IARI) has confirmed that the mysterious disease resulting in “dwarfing” of rice plants, reported mainly from Punjab and Haryana, has been caused by the Southern Rice Black-Streaked Dwarf Virus (SRBSDV). The virus is spread by the white-backed plant hopper, an insect pest, which injects it while sucking the sap from mostly young plants.

“The presence of the virus was detected both in the infected plants and the body of the vector insect, whose RNA was isolated. But the virus was not found in the seeds collected from the infected plants. The virus is specific to the phloem (plant tissues that transport sugar and organic nutrients from the leaves to other parts) and is not transmitted by seed or grain,” A K Singh, director of IARI

An IARI team surveyed a total of 24 fields in Sonepat, Panipat, Karnal, Kurukshetra, Ambala and Yamunanagar districts of Haryana. In the fields where the disease was recorded, the infected plants varied from 2 to 10 per cent. In a severely-affected field in Panipat, up to 20 per cent incidence was recorded.

“The affected plants showed severely stunted appearance. The roots were poorly developed and turned brownish. The infected tillers can be easily pulled out,” the IARI said in its report that has been submitted to the Union Agriculture Ministry.

The institute carried out a comprehensive investigation to diagnose the cause of the mystery “dwarfing” disease, using three independent methods: transmission electron microscopy, RT-PCR and real-time quantitative PCR.

The first method indicated the presence through visualisation of the SRBSDV, which belongs to the Fijivirus genus and was first detected in China in 2008. The second method confirmed it by “using specific primers targeting two different genomic components of the virus”. The third “further validated” the infection in the symptomatic samples and the white-backed plant hopper vector, besides confirming the absence of the virus in the seeds collected from the plants.

The IARI investigation has revealed the infection in as many as 12 rice varieties, both basmati (Pusa-1962, 1718, 1121, 1509, 1847 and CSR-30) and non-basmati (PR-114, 130, 131, 136, Pioneer Hybrid and Arize Swift Gold). “In general, the non-basmati varieties were more affected than basmati. Also, the late-sown paddy had less infestation than the early sown,” the report said.
Given that the virus is exclusively transmitted by the white-backed plant hopper, the IARI has advised farmers to monitor the fields every week for the presence of the insect. The pest can be managed by spraying recommended dosages of ‘buprofezin’, ‘acetamiprid’, ‘dinotefuran’ or ‘flonicamid’ insecticides at 15-day intervals.

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