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The Punjab Agricultural University has found southern rice black-streaked dwarf virus (SRBSDV), a viral disease, behind the stunting of paddy plants in many parts of Punjab.
This is the first time that SRBSDV, which was first reported in 2001 from Southern China, has been detected in Punjab.
Ludhiana-based PAU vice-chancellor Satbir Singh Gosal said that SRBSDV is the real cause behind stunting of rice.
The PAU scientists had received complaints of stunted rice plants from farmers.
Preliminary reports about the occurrence of these symptoms started coming from the districts of Sri Fatehgarh Sahib, Patiala, Hoshiarpur, Ludhiana, Pathankot, SAS Nagar, and Gurdaspur.
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Within one month, stunted rice plants were observed in almost the whole of Punjab and its adjoining states, said the PAU in a statement here.
"The infected plants were stunted with narrow erect leaves, with both roots and shoots of the plants severely affected. In severely infected rice fields, the infected plants showed withering, it said.
The height of the stunted plants showed reduction from one-half to one-third than the normal plants. These plants had shallow roots and could be easily uprooted. These plants were observed in almost all the cultivated varieties in the farmer's fields, it said.
The team of PAU scientists visited the affected areas in the districts of Hoshiarpur, Ropar, Mohali, Ludhiana, Sri Fatehgarh Sahib and Patiala for systematically deciphering the cause behind these stunted plants in rice.
The team observed that the incidence was more pronounced in early sown paddy crop irrespective of the variety. The date of sowing trials at PAU substantiated that 15-25 June transplanted rice crop was more affected than the later dates, said the PAU.
The stunting symptoms were observed in 5-7 per cent of the fields in these districts. In the affected fields, the incidence of stunted plants ranged from 5-7 per cent, it said.
The incidence of SRBSDV is the first viral disease in Punjab.
"SRBSDV is a double standard RNA virus that was first reported in 2001 from Southern China. The symptoms produced on the rice as well as the genome structure of this virus resembles with that of rice black streaked dwarf virus but as this virus was first reported from the Southern China, this virus was named as southern rice black-streaked dwarf virus," it said.
"As per the earlier published scientific reports from elsewhere, SRBSDV is transmitted by white backed plant hopper (WBPH) in persistent circulative and propagative manner," it further said.
The analysis of soil and plant samples collected from the affected fields showed no relationship of stunting with nutrition deficiency.
The collected plant samples from different fields were further analyzed for the detection of different rice pathogens including nine viruses and one phytoplasmas, said the PAU.
"The laboratory analysis was carried out using PCR-based molecular markers specific for each of the nine rice viruses and one phytoplasma that are reported to infect the rice crop worldwide.
These markers revealed the presence of SRBSDV in the analyzed samples. However, none of the markers specific to the other viruses could amplify in any of the samples. It gave initial indication of SRBSDV association with stunting in rice, said the PAU.
The PAU scientists said as there is no corrective measure for the viral diseases, the only way out is to adapt preventive measures for managing the vector of this viral disease.
"Farmers should regularly monitor the rice crop for the presence of WBPH. A few plants in the field should be slightly tilted and tapped 2-3 times at the base at weekly intervals. WBPH nymphs or adults, if present, will be seen floating on water, said the PAU while advising farmers to spray insecticide on observing the WBPH.
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