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Coffee leaf rust (Hemileia vastatrix) Photo: placeholder pending image-fill pass

Coffee leaf rust (Hemileia vastatrix)

Coffee leaf rust (CLR), caused by the obligate biotrophic basidiomycete Hemileia vastatrix Berkeley & Broome, is the single most damaging disease of arabica coffee worldwide and the principal driver of varietal change in Indian arabica plantations. The pathogen, first described in Sri Lanka in 1869, destroyed the entire Ceylon arabica industry by the 1880s and has driven the development of every modern Indian arabica selection from S.795 onward.

Identification and symptoms

  • Pathogen: Hemileia vastatrix, order Pucciniales (rust fungi)
  • Symptoms: small chlorotic spots on underside of leaves enlarge into orange-yellow powdery uredinial pustules 1-2 cm across; corresponding chlorotic halo on the upper surface
  • Progression: heavily infected leaves abscise prematurely, exposing berries to sun-scald and crop loss in the following season
  • Diagnostic feature: powdery orange urediniospores wash off easily, distinguishing CLR from brown eye-spot

Hosts and life cycle

CLR is host-specific to Coffea species, with arabica highly susceptible and robusta resistant. Urediniospores germinate on the under-surface of leaves at 22 °C in the presence of free water; latent period is 25-35 days. Multiple physiological races (designated I, II, III etc.) exist; race II is the most widely distributed in India and overcomes the SH4 gene found in some early selections. New races regularly erode existing host resistance.

Damage and economic impact

In susceptible blocks under heavy monsoon conditions, defoliation of 30-50% can occur, with yield loss the following year of 30-50%. Indian arabica was severely damaged by a virulent rust epidemic in the 1980s and again in 2014-15; estate-level losses drove large-scale replanting from older Kent-type selections to rust-tolerant CCRI material — Coffee Arabica Cauvery Catimor in particular.

Management

  • Resistant varieties: Coffee Arabica S 795 Selection (tolerant), Coffee Arabica Cauvery Catimor (Catimor-derived, leaf-rust resistant), Coffee Arabica Sln 9 Saln 12 (S.795 × hybrid Timor derivative), Coffee Arabica Chandragiri (Catimor)
  • Cultural: judicious shade-tree pruning to improve under-canopy air drainage; balanced N-P-K nutrition; avoid excessive nitrogen
  • Chemical: pre-monsoon and post-monsoon prophylactic sprays of Bordeaux mixture 0.5% (copper sulphate + lime); systemic fungicides hexaconazole 0.1% or triadimefon 0.1% at first sign of pustules; copper oxychloride 0.25% as alternate
  • Sanitation: collection and burning of fallen infected leaves at the end of the monsoon to reduce inoculum

See also: Coffee Arabica S 795 Selection, Coffee Arabica Cauvery Catimor, Coffee Arabica Sln 9 Saln 12, Coffee Arabica Chandragiri, Coffee Arabica Vs Robusta India, Coffee Shade Cultivation Silver Oak.

Sources

  1. Leaf Rust Management - CCRI Balehonnur. Central Coffee Research Institute.
  2. Coffee Board Plant Pathology Bulletin. Coffee Board of India.