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Redgram wilt (Fusarium udum, udum vyaadhi)

Redgram wilt — locally called udum vyaadhi in some Telangana districts — is caused by the soilborne fungus Fusarium udum Butler. It is the single most damaging disease of pigeonpea in India, responsible for 20-100% plant mortality in susceptible-variety fields on wilt-sick soils. The disease accounts for an estimated annual loss of around Rs 8,000 crore worth of grain across the Indian pigeonpea belt according to ICRISAT and ICAR-IIPR estimates.

Pathogen and identification

F. udum is a vascular wilt pathogen that colonises the xylem and blocks water transport. Diagnostic field symptoms appear in patches and worsen from flowering onward:

  • Wilting and yellowing of one half of the plant — characteristic partial wilt — followed by complete wilt
  • Purple-brown vascular discoloration when the stem is split longitudinally near the collar; the band runs continuously up the xylem
  • Black streaks in the lower stem and tap-root cortex
  • Patchy mortality in the field, often along rows or in low-lying spots where infested debris accumulated

Confirmation in lab requires isolation on Komada's selective medium and microscopic identification of macroconidia and chlamydospores.

Hosts and lifecycle

The pathogen survives in soil as chlamydospores for 5-10 years and on infected crop residues. It infects pigeonpea roots from the soil and progresses through the vascular system. Infection is enhanced where:

  • Pigeonpea is grown continuously on the same field
  • Temperatures during early growth are 17-25 deg C with intermittent moisture
  • Soil pH ranges 6.0-7.0 (typical Deccan red-loam range)
  • Root injury from nematodes, especially Heterodera cajani and Meloidogyne incognita, opens infection courts

The fungus is also seed-borne at low levels.

Damage and economic impact

In wilt-sick black-soil pigeonpea tracts of north Karnataka (Gulbarga, Bidar), Marathwada (Latur, Osmanabad), Telangana (Mahabubnagar) and Vidarbha (Yavatmal, Akola), unprotected susceptible cultivars lose 40-60% of plant stand and 50-100% of pod yield. In the early 1970s and 1980s wilt epidemics on TS-3 and S-5 led to large-scale shift to wilt-resistant cultivars Maruti, BDN-1, BDN-711.

Management

  • Resistant varieties (primary line of control): Maruti (ICP-8863), Asha (ICPL 87119), PRG 176, BSMR-853, BDN-711, IPA-203, GRG 152. Choose a variety that combines wilt and sterility-mosaic resistance for the Deccan plateau.
  • Cultural practices: 3-4 year rotation with non-host cereals (sorghum, pearl millet, maize); avoid back-to-back pigeonpea on wilt-sick fields; uproot and burn wilted plants before sporulation; deep summer ploughing to expose chlamydospores
  • Soil health: incorporate FYM and crop residue to build Trichoderma and Pseudomonas populations; raised-bed or BBF layout on heavy soils to improve drainage
  • Biological seed treatment: Trichoderma viride or Trichoderma harzianum at 4-6 g/kg seed, followed by Pseudomonas fluorescens at 10 g/kg
  • Chemical seed treatment: carbendazim 50 WP at 2 g/kg + thiram 75 WP at 2 g/kg, or carboxin 37.5 + thiram 37.5 WS at 3 g/kg seed
  • Soil drenching: in nurseries and patch outbreaks, drench with carbendazim 1 g/L

A combined seed-treatment + resistant-variety + 4-year rotation package is the ICAR-IIPR standard recommendation.

See also: Redgram crop overview, Maruti redgram, Asha (ICPL 87119), PRG 176, Pod borer in pulses.

Sources

  1. Fusarium wilt of pigeonpea: management. ICAR-Indian Institute of Pulses Research, Kanpur.
  2. Pigeonpea wilt (Fusarium udum). ICRISAT, Patancheru.
  3. Fusarium udum factsheet. CABI Plantwise.