- Tungro can appear at any time right from seedling stage.
- The extent of crop damage and yield loss depends on the growth stage at the time of the virus infection.
- The major symptoms of tungro are stunting and change in colour of leaves to different shades of yellow or orange.
- The degree of these symptoms varies with variety, environmental condition, age of the plant and strain of virus. Stunting is generally slight but very pronounced in susceptible varieties. There is only slight decrease in tiller number.
- The change in colour starts from tip and progress downward for a short distance.Sometimes the whole leaf is discoloured.Small rust coloured spots may appear on older leaves.
- In moderately resistant varieties the discolouration conspicuous at one stage may gradually disappear at later stages.This is referred to as recovery from the disease.
- Plants infected during early stages of growth are more damaged than those that are attacked later. Flowering is delayed in infected plants and production of grain is affected.
- Diseased plants have fewer spikelets than healthy plants, a higher proportion of empty grains, lower grain weight and discoloration of grains.Plants infected at late stages of growth may not show symptoms before harvest.But symptoms may appear in the ratoon shoots.
- Rice tungro is caused by simultaneous infection of two different viruses: Rice tungro bacilliform virus (RTBV) having a double stranded circular DNA genome and Rice tungro spherical virus (RTSV) having a single stranded RNA genome.
Select 4 one square meter plot at random. From each square metre observe five hills at random and estimate the percentage of damage.