Blast

Blast :Magnaporthe oryzae (formerly Magnaporthe grisea)
anamorph: (Pyricularia oryzae)

Symptoms:

• Above ground parts of the rice plant (leaves,  nodes and neck) are attacked by the fungus
• Initial symptoms are white to gray-green lesions or spots with brown borders
• Small specks originate on leaves – subsequently enlarge into spindle-shaped spots (0.5  to 1.5 cm length and 0.3 to 0.5 cm width) with the ashy centre.
• Older lesions are elliptical or spindle-shaped and whitish to grey with necrotic borders. Several spots coalesce to form big irregular patches.
• Nodal infection causes the culm to break at the infected area
• Internodal infection also occurs at the base of the plant which causes white panicles similar to that induced by yellow stem borer or water deficit
• Lesions on the neck are greyish brown and causes the girdling of the neck and the panicle to fall over
• If infection of the neck occurs before milky stage, no grain is formed, but if infection occurs later, grains of poor quality are formed
• Lesions on the branches of the panicles and on the spikelet pedicels are brown to dark brown
• The size and shape of the spots vary on different rice varieties.

 

Identification of pathogen:

• This disease is caused by a fungus named Pyricularia oryzae, which overwinters in rice seeds and infected rice stubble.
• The fungus reproductive structures, spores, can spread from these two sources to rice plants during the next growing season and initiate new infections.
•  Spores from these new infections can spread by the wind to other rice plants over great distances.
• The conidiophores of the pathogen are produced in clusters from each stoma. They are rarely solitary with 2-4 septa. The basal area of the conidiophores is swollen and tapers toward the lighter apex.
• The conidia of the fungus measure 20-22 x 10-12 µm. The conidia are 2-septate, translucent and slightly darkened. They are obclavate and tapering at the apex. The perfect stage is rarely found in the field.

 

Management:

Cultural methods

• Planting resistant varieties against the Rice blast is the most practical and economical way of controlling rice blast.
• Use of tolerant varieties (CO 47, CO 50, ADT 36, ADT 37, ASD 16, ASD 20, ADT 39, ASD 19, TPS 3, White ponni, ADT 44, IR 64 and IR 36)
• Avoid excess N – fertilizer application
• Apply nitrogen in three split doses.
• Remove weed hosts from bunds.

Preventive methods

• Avoid dry nurseries.
• Avoid late planting.
• Burning of straw and stubbles after harvest
• Avoid grasses and other weeds on bunds and inside.

Chemical methods

• Dry seed treatment

• Thiram or captan or carboxin or carbendazim at 2 g/kg of seeds.
• Treat the seeds at least 24 hours prior to soaking for sprouting.
• The treated seeds can be stored for 30 days without any loss in viability.

• Wet seed treatment

• Carbendazim or Tricyclozole at 2 g/lit of water for 1 kg of seed.
• Soak the seeds in the solution for 2 h
• Drain the solution, sprout the seeds and sow in the nursery bed.
• This wet seed treatment gives protection to the seedlings up to 40 days from seedling disease such as blast and this method is better than dry seed treatment or
• Treat the seeds with talc based formulation of P. fluorescens (Pf1) @ 10g/kg of seed and soak in 1lit of water overnight.
• Decant the excess water and allow to sprout the seeds for 24 h and then sow.

• Seedling dip with Pseudomonas fluorescens

• Stagnate water to a depth of 2.5cm over an area of 25m2 in the main field. Sprinkle 2.5 kg of the talc based formulation of Pseudomonas fluorescens (Pf1) and mix with stagnated water. The seedlings pulled out from the nursery is to be soaked for 30 min. in thestagnated water and then transplanted.

(Note: Biocontrol agents are compatible with biofertilizers; Biofertilizers and biocontrol agents can be mixed together for seed soaking; Fungicides and biocontrol agents are incompatible)

• Carbendazim 50WP @ 500g/ha (or)
• Tricyclozole 75 WP @ 500g/ha (or)
• Metominostrobin 20 SC @ 500ml/ha (or)
• Azoxystrobin 25 SC @ 500 ml/ha
• Seed Treatment with TNAU Pf 1liquid formulation @ 10 ml/kg of seeds
• Soil application with TNAU Pf1 liquid formulation (500ml/ha)
• Foliar spray with TNAU Pf1 liquid formulation @ 5ml/lit.
• Do not apply higher doses of fungicides.
• Spray before 11.00 am or after 3.00 pm.
• Avoid noon hours for spraying.

 

 

Source-

• TamilNadu Agritech Portal