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Diseases

Diseases
11
Jul

Favourable conditions for Sheath Blight of Rice disease

High relative humidity (96-97 per cent), high temperature (30-32OC), closer planting and heavy doses of nitrogenous fertilizers.

File Courtesy: 
BAU Ranchi
11
Jul

Pathogen for Sheath Blight of Rice disease

1. Rhizoctonia solani (Sexual stage : Thanetophorus cucumeris)
2. The fungus produces usually long cells of septate mycelium which are hyaline when young, yellowish brown when old.

3. It produces large number of globoses sclerotia, which are initially white, later turn to brown or purplish brown.

File Courtesy: 
BAU Ranchi
11
Jul

Sheath Blight of Rice disease

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Symptoms:

1. The fungus affects the crop from tillering to heading stage. Initial symptoms are noticed on leaf sheaths near water level. On the leaf sheath oval or elliptical or irregular greenish grey spots are formed.

2. As the spots enlarge, the centre becomes greyish white with an irregular blackish brown or purple brown border .

File Courtesy: 
BAU Ranchi
Photo Courtesy: 
BAU Ranchi
11
Jul

Management of Brown Leaf Spot of Rice

- Field sanitation: Removal of collateral hosts and infected debris in the field.
- Crop rotation, adjustment of planting time and proper fertilization are suggested.
- Use of slow release nitrogenous fertilizers is advisable.
- Use disease free seeds.
- Resistant variety: Grow disease tolerant varieties like Birsamati, Birsa Vikas Dhan 110, Birsa Vikas Dhan 109, Hazaridhan, Sadabahar, Birsa Dhan 108, Shivam, Virendra, Sugandha and Rajashri showed resistance against brown leaf spot of rice.
- Seed Treatment: with Carbendazim 50 WP or Beam (Tricyclazole) @ 2 gm/kg seed.

File Courtesy: 
BAU Ranchi
11
Jul

Mode of Spread and Survival of Brown Leaf Spot of Rice

1. The infected seeds are the most common source of primary infection. The conidia present on infected grain and mycelium in the infected tissue may viable for 2 to 3 years.

2. The fungus may survive in the soil for 28 months at 30OC and 5 months at 35OC. Airborne conidia infect the plants both in nursery and in main field.

3. Maximum flight of conidia take place at a wind velocity of
4.0 - 8.8 hr. Minimum temperature of 27 -28OC, Relative humidity of 90-99% and rainfall of 0.4 -14.4 mm favored the dispersal of the conidia to maximum extent.

File Courtesy: 
BAU Ranchi
11
Jul

Favourable Conditions for Brown Leaf Spot of Rice

1. Temperature of 25-30OC with relative humidity above 80 per cent are highly favourable. Excess of nitrogen aggravates the disease incidence.

File Courtesy: 
BAU Ranchi
11
Jul

Pathogen for Brown Leaf Spot of Rice

1. Helminthosporium oryzae (Syn : Drechslera oryzae) (Sexual stage : Cochliobolus miyabeanus).
2. H. oryzae produces greyish-brown to dark brown septate mycelium. Conidiophores may arise singly or in small groups.
3. They are straight, sometime geniculate, pale to brown in colour. Conidia are usually curved with a bulge in the centre and tapering towards the ends occasionally almost straight, pale olive green to golden brown colour and are 6-14 septate.

File Courtesy: 
BAU Ranchi
11
Jul

Brown Leaf Spot of Rice

Symptoms:
1. The fungus attacks the crop from seedling in nursery to milk stage in main field. Symptoms appear as lesions (spots) on the coleoptile, leaf blade, leaf sheath, and glume, being most prominent on the leaf blade and glumes.
2. The disease appears first as minute brown dots, later becoming cylindrical or oval to circular The several spots coalesce and the leaf dries up.
3. The seedlings die and affected nurseries can be often recognised from a distance by their brownish scorched appearance.

File Courtesy: 
BAU Ranchi
11
Jul

Management of Rice Blast disease

Remove and destory the weed hosts in the field bunds and channels.
Seed Treatment: with Carbendazim 50 WP or Beam (Tricyclazole) @ 2 gm/kg seed.
Seed treatment with biocontrol agent: Trichoderma viride@ 4g/kg or Pseudomonas fluorescens @ 10g/kg of seed.
Avoid close spacing of seedlings in the main field.
Spray the nursery with Carbendazim 25 g or Edifenphos 25 ml for 8 cent nursery.
Spray 0.1% solution of Carbendazim 50 WP (@ 1 gm/lt water) or 0.06% Beam (Tricyclazole) (6 gm/10 lt water).

File Courtesy: 
BAU Ranchi
11
Jul

Forecasting of Rice Blast disease

1. Forecasting blast of rice can be made on the basis of minimum night temperature range of 20-260C in association with a high relative humidity range of 90 per cent and above lasting for a period of a week or more during any of the three susceptible phases of crop growth, viz., seedling stage, post transplanting tillering stage and neck emergence stage.

2. In Japan, the first leaf blast model was developed and named as BLAST. Later based on different field experiments various models were developed namely, PYRICULARIA, PYRIVIEW, BLASTAM, EPIBLA and P BLAST.

File Courtesy: 
BAU Ranchi
11
Jul

Mode of Spread and Survival of Rice Blast

1. The disease spreads primarily through airborne conidia since spores of the fungus present throughout the year.

2. Mycelium and conidia in the infected straw and seeds are important sources of inoculum. Irrigation water may carry the conidia to different fields.

3. The fungus also survives on collateral hosts viz., Panicum repens, Digitaria magrginata, Brachiaria mutica, Leersia hexandra, Dinebra retroflea, Echinochloa crusgalli and Stenotaphrum secondatum.

File Courtesy: 
BAU Ranchi
11
Jul

Favourable Conditions for Rice Blast disease

1. Application of excessive doses of nitrogenous fertilizers, intermittent drizzles, cloudy weather, high relative humidity (93-99 per cent), low night temperature (between 15-20OC or less than 26OC), more number of rainy days, longer duration of dew, cloudy weather, slow wind movement and availability of collateral hosts.

File Courtesy: 
BAU Ranchi
11
Jul

Pathogen for Rice Blast disease

1. Pyricularia oryzae (Syn : P. grisea) (Sexual stage : Magnaporthe grisea)

2. Mycelium of the fungus, is hyaline to olivaceous, septate and highly branched. Conidia are produced in clusters on long septate, olivaceous slender conidiophores.

3.Conidia are obpyriform to ellipsoid, attached at the broader base by a hilum. Conidia are hyaline to pale olive green, usually 3 celled.

4. The perfect state of the fungus is M. grisea. It produces perithecia. The ascospores are hyaline, fusiform, 4 celled and slightly curved.

File Courtesy: 
BAU Ranchi
11
Jul

Rice Diseases

Rice crop of different regions within Jharkhand state is attacked by five major diseases. They are:
1. Rice Blast
2. Brown Leaf Spot of Rice
3. Sheath Blight of Rice
4. Bacterial Leaf Blight (BLB) of Rice
5. False Smut of Rice

File Courtesy: 
BAU Ranchi
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