Blast diseases were first time recorded in China in 1637.in Japan, it is believed to have occurred as early as in 1704. In Italy, this disease was recorded in 1828 for the name of brusone. And in the USA, it was recorded in 1876. The disease was first recorded in India from Tanjore district of Tamil Nadu in 1978.
Rice blast is also known as magnsporthe grisea. The fungus is known to occur in 85 countries worldwide. Rice blast causes economically significant crop losses annually.
Economic importance: Rice blast is the most important disease concerning the rice crop in the world. Since rice is an important food source for much of the world, it’s effects have a broad range. Every year the number of crops lost to rice blast could feed 60 million people worldwide. The pathogen causes yield loss ranging from 30-61 % depending upon the stage of infection. In severe cases, losses amounting to 70-80 % of grain yield are reported.
This disease fungus attacks the crop at all stages from seedlings in the nursery to heading in the main field. The typical symptoms appear on leaves, leaf sheath, rachis, nodes, and even the glumes are also attacked.
Types of Blast disease :
together as the disease progresses and large areas of the leaves dry up and wither. Similar spots are also formed on the sheath. Severely infected nursery and field show a burnt appearance.
■ leaf blast: on the leaves, the lesions start as small water-soaked bluish-green specks, soon enlarge and from characteristics spindle-shaped spots with a grey center and dark brown margin. The spots join
Node blast: in this case nodes are infected, irregular black areas that encircle the nodes can be noticed. The affected nodes may break up and all the plant parts above the infected nodes may die (Node blast ).
■ Neck blast: At the flower emergence, the fungus attacks the peduncle which is engirdled, and the lesion turns to brownish-black. In early neck infection, grain filling does not occur and the panicle remains erect like a dead heart caused by a stem borer. In the late
Neck/panicles blast of rice
infection, partial grain filling occurs. In the case of heavily infected panicles, small brown to black spots also may be observed on glumes.
Favorable conditions: Application of excessive doses of nitrogenous fertilizers, cloudy weather, high relative humidity (93-99)%, intermittent drizzles, more number of rainy days, low night temperature (between 15-20°c or less than 26°c), longer duration of dew, cloudy weather, slow wind movement and availability of collateral hosts.
Forecasting: forecasting blast of rice can be made based on minimum night temperature range of 20-26 °c in association with a high relative humidity range of 90 % and above lasting for a period of a week or more during any of the three susceptible phases of crop growth, viz, seedlings stage, post transplanting tillering stage and neck emergence stage.the first leaf model was developed and named as BLAST in Japan.
Management: •Grow resistant varieties like Resistant to leaf and neck blast disease: chhomrong,machhapuchhre-3,lekali dhan-3,lumle -2, Chandannath-1&3 • resistant to blast disease: Khumal -4
- use of seeds from a disease-free crop.
- remove destroy the weed hosts in the field bunds and channels.
- split application of nitrogen and judicious application of nitrogenous fertilizers
- keeping water in the field.
- Treat the seeds with captan or thiram or carbendazim or carboxin or tricyclazole at the rate of 2g/kg of seeds.
- spray the nursery with biocontrol agent Trichoderma viride @4g/kg and avoid close spacing of seedlings in the field.
- spray the nursery with carbendazim 25g or Edifenphos 25 ml.
- spray the main field with Edifenphos @0.1% or carbendazim @0.1% or Thiophanate methyl @0.1% or Tricyclazole 75% with 0.75g/lit. water or sugamysen 3% SL. 9.5 ml/lit. water.
Writer : Sirpat Badhai