Rice blast and neck blast (Magnaporthe oryzae)

Rice blast is caused by the ascomycete Magnaporthe oryzae (anamorph Pyricularia oryzae). It is one of the most economically important diseases of rice worldwide and the principal foliar disease driving fungicide use in Indian paddy.

Identification and symptoms

Leaf blast lesions are diagnostic: spindle-shaped, grey-centred with brown margins, on the leaf blade. Node infections rot internodes and snap stems. Most damaging is neck blast, where the panicle base (neck) is colonised, causing the entire panicle to collapse and turn white - locally called manipandu. Collar and grain blast are additional phases.

Host crops and life cycle

The fungus produces airborne conidia that disperse on wind and dew. Inoculum survives on stubble, infected seed and grassy hosts. Epidemics build under cool nights, prolonged dew, dense canopies and high nitrogen rates - conditions common in rabi/yasangi paddy in Telangana and parts of Andhra Pradesh.

Damage and economic impact

Leaf blast reduces photosynthetic area; neck blast can cause near-total panicle loss when it appears at heading. Susceptible varieties under conducive weather routinely experience large yield losses, justifying preventive sprays at booting on at-risk lines.

Management

Resistant varieties: Rnr 15048 (Telangana Sona) and Drr Dhan 75 are blast-resistant lines positioned as replacements for susceptible older cultivars.
Cultural: balanced and split nitrogen, wider spacing, and avoiding susceptible varieties in known endemic blocks.
Chemical: tricyclazole 70% WP is the standard preventive; combination fungicides such as trifloxystrobin + tebuconazole and isoprothiolane reduce disease index by 70-80% in published field trials. Sprays at boot (Paddy Panicle Stage Management) are critical for neck blast control.

References

Management of rice blast with modern combination fungicides. Vegetos.
Field evaluation of fungicides for rice blast. J. Res. ANGRAU (ICAR).