Tungro Disease in Rice cultivation: A Viral Disease

                        Rice is a major staple food of the world's population, covering about 20% of total  calorie consumed. Its cultivation is a way of life for more than 70% of farmers in Asian countries, in the form of employment, income and food. These countries contribute 90% world's rice production. China is the largest producer of rice with highest yield per Hectare. Though India occupies largest area under rice cultivation, but ranks second in total production. Indonesia, Bangladesh, Vietnam are other major countries producing rice. No doubt  rice is rich source of carbohydrates, but also contain fair amount of proteins (2.5%). Like any other crop, it also suffers from incidences of plenty of diseases, may be fungal or bacterial or viral kind.  Tungro is one such disease which may cause considerable quantitative and qualitative losses.

Symtoms of Rice Tungro Disease:

          Main symptoms of Tungro disease is yellowing of leaves. Yellowing starts from tip of leaves located at the base, extends downwards along the leaf edge to cover entire leaves later on. Discoloration varies depending on the cultivars. It is normal yellow in Japonica and brighter yellow or orange yellow in case of Indian varieties. Small rusty spots appear on affected leaves in severe cases. Incidence of disease is more in early stages of plant, sometimes as early as at seedling stage. Affected plants produce less number of tillers and tillers with shortened length. Occurrence of disease delays flowering, panicles initiation and maturity. Panicle length remains short and grains formed may not be wholesome and of  less weight. Sometimes grains exhibits dark blotches.

Management of Rice Tungro Disease:

Cause of Rice Tungro Disease:

       'Tungro' is the word from Philippino language, means 'degenerated Growth'. The disease was misunderstood earlier to nutrient deficiency. It was first demonstrated as viral disease in 1963 in Philippines. Mainly the  disease is caused by tow types of virus particles like 'Rice Tungro Spherical Virus (RTSV)' and 'Rice Tungro Bacilliform Virus (RTBV)'. These virus particles are transmitted by green or plant hoppers, especially Niphotettix virescenns. RTBV is a rod shaped, DNA congaing virus, where as RTSV is spherical in shape with RNA as its constituent. RTSV can be transmitted individually  by vector, where as RTBV only in combination with RTSV.

• Use of Resistant varieties: Cultivation of rice varieties resistant to either development of nymphs and adult vectors or tolerant to Tungro virus is the best way manage this disease. Varieties like IR 36, IR 50, ADT 37, CO 45, CO 48, etc have been found effective in this regard. The variety Nidhi (IET 9994) has been found highly resistant to said virus. Kataribhog, Ambemohar 102, Vikramarya (IET 7302) are the some of the other known resistant varieties.

• Fallowing and crop rotation: Incidences of the disease to be followed by fallowing of land for few months or a season to avoid possible build up and growth of vector populations. Crop rotation with legumes, oil seeds,   tuber crops often found effective.

• Weeding: Regular weeding is mandatory to destroy alternate host plants. This reduces the chance for vector survival. Keeping the farm bunds free from weeds and grasses are also very important.

• Proper nutrition of crops: As incident of disease occurs in early stages of crops, proper nutrition keeps the plant vigor intact and make them immune to virus. Application of nitrogenous fertilizer in required quantity reduces associated leaf yellowing to some extent and application of phosphorus and potash keep the crop less susceptible to Tungro virus.

• Control of Hoppers: Hoppers, which are the vectors of the Tungro disease can be controlled well by using light traps. Here hoppers are made to attract towards lights and accumulate and the same are killed by applying suitable insecticides. To reduce the hopper infestation during the seedling stage, application of carbofuran 3G@ 30 kg/ha is recommended before sowing or broadcast the same after 4-5 days of sowing. Foliar spray can be made with Monocrotophos 36EC @1 L/ha or Carboryl 50 WP @2 kg/ha depending on hopper population, in post transplanting stage.