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Groundnut rust (Puccinia arachidis) Photo: LandCare Ltd., New Zealand · CC BY-SA 3.0 · source ↗

Groundnut rust (Puccinia arachidis)

Groundnut rust is caused by the obligate biotrophic fungus Puccinia arachidis Speg. It is the third major foliar disease of groundnut alongside early and late leaf spot, and frequently appears as a co-epidemic with late leaf spot. Combined rust + late leaf spot losses can exceed 50-70 percent pod yield in susceptible varieties, per ICRISAT and ICAR-DGR multi-location trials.

Identification

The diagnostic symptom is the orange-brown to cinnamon-coloured pustule (uredinium) on the lower surface of leaflets. Pustules are 0.5-1.4 mm, often surrounded by a chlorotic halo, and rupture to release powdery urediniospores that stain the fingers when touched. As the disease advances, leaves turn yellow, become brittle and drop prematurely. On heavily infected plants the entire canopy can look rusty-orange from a distance.

Hosts and lifecycle

In India only the uredinial (repeating) stage occurs; no functional teliospores or alternate host has been identified, so the fungus survives between seasons on volunteer plants, ratoon stubble and infected debris. Urediniospores are wind-dispersed over long distances and require 6-12 hours of leaf wetness with temperatures of 20-28 deg C to germinate and infect. The latent period is 10-12 days, allowing rapid epidemic build-up under monsoon humidity.

Damage and economic impact

Rust differs from leaf spots in that it does not cause defoliation until very late; instead it reduces pod fill by destroying photosynthetic tissue. Pod yield losses of 30-70 percent and haulm yield losses of 15-40 percent are documented. In Anantapur and Chittoor the disease is most severe in late-sown kharif crops and in rabi-summer groundnut where the rust carries over from kharif debris.

Management

  • Resistant varieties: ICGV 86590, ICGV 87160, ICGV 91114 and Kadiri-9 carry useful field resistance from ICRISAT germplasm. Stack with late-leaf-spot resistance because the two diseases occur together.
  • Cultural: rogue volunteer groundnut plants; do not grow consecutive groundnut crops in the same field; destroy crop debris after harvest; avoid late sowing in rust-endemic tracts.
  • Chemical: prophylactic sprays of mancozeb 75 WP at 2 g/L or chlorothalonil 75 WP at 2 g/L starting 45-50 DAS. Once rust is established, use systemic triazoles: tebuconazole 25 EC at 1 ml/L, propiconazole 25 EC at 1 ml/L, or hexaconazole 5 EC at 2 ml/L. Combination products such as tebuconazole + trifloxystrobin (Nativo 75 WG) at 0.4 g/L give the best control in AICRP-Groundnut trials, and are usually applied at 15-day intervals.

Because rust and late leaf spot share weather requirements and timing, ICAR-DGR's standard recommendation is a unified 3-spray schedule starting at 50 DAS that controls both diseases simultaneously.

See also: Tikka leaf spot in groundnut, Late leaf spot, Groundnut crop, Kadiri 6 groundnut.

Sources

  1. Rust of groundnut technical bulletin. ICAR-Directorate of Groundnut Research, Junagadh.
  2. Puccinia arachidis factsheet. CABI Plantwise.
  3. Groundnut rust and late leaf spot bulletin. ICRISAT, Patancheru.