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Chickpea ascochyta blight (Ascochyta rabiei)

Ascochyta blight of chickpea is caused by the fungus Ascochyta rabiei (teleomorph Didymella rabiei). In India it is the principal foliar disease of chickpea in the cool-humid North-West Plains Zone — Punjab, Haryana, Himachal Pradesh, parts of Jammu & Kashmir, and northern Rajasthan — and is the main biotic constraint on kabuli chickpea expansion in these zones. Documented epidemics in Punjab and HP (1980-82, 1995, 2013) caused 70-100% crop loss on susceptible cultivars; in most years losses range 10-30% when control is delayed.

Pathogen and identification

A. rabiei is an air- and rain-splash-dispersed ascomycete that overwinters as pycnidia on chickpea debris and as chlamydospores in soil. The teleomorph (sexual stage) produces ascospores on overwintered debris in spring, providing primary inoculum that travels several kilometres. Diagnostic symptoms:

  • Leaf lesions: small, round to oval, light-brown spots with dark margins; pycnidia in concentric rings give a characteristic "target-board" appearance
  • Stem lesions: elongated, dark-brown to black girdling cankers at internodes; girdled stems break and the upper plant collapses
  • Pod lesions: sunken brown spots with pycnidia; seed infection through pods causes brown shrunken seed
  • Field pattern: foci of dead/girdled plants enlarging from infected spots after cool moist weather; entire fields can be blighted in 10-14 days under epidemic conditions

Optimum disease conditions are 15-22 deg C, relative humidity above 70%, and 6+ hours of leaf wetness. The pathogen has pathotype variation; pathotypes II and III dominate the North-West Plains.

Hosts and lifecycle

Chickpea is the principal host; wild Cicer species can also be infected. Primary inoculum comes from infected seed (5-10% transmission), crop debris (pycnidia survive 2-3 years), and ascospores from the sexual stage on overwintered residue. Secondary spread is by rain-splash conidia. Late-sown, dense crops in foggy/rainy Decembers and cool-humid March weather face the highest risk.

Damage and economic impact

In Punjab, Haryana and HP, ascochyta blight regularly contributes to inter-annual chickpea area volatility, deterring kabuli expansion despite premium prices. Susceptible cultivars lose 30-100% pod yield in epidemic years; even moderately resistant varieties need 1-2 fungicide sprays in humid seasons. The disease has been the principal driver of the shift of chickpea cultivation from the North-West Plains to drier central and peninsular India over the past three decades.

Management

  • Resistant varieties: GNG 469, GNG 663 (Samrat), GNG 1581, GNG 1969, GPF 2, PBG 5, PBG 7, GL 26054, HC 1; ICARDA-bred FLIP lines used in NWPZ breeding; for kabuli — PBG 1, HK 4, GLK 28127
  • Healthy seed: use ascochyta-tested certified seed; rogue infected plants in seed-production plots
  • Seed treatment: carbendazim 1 g + thiram 2 g per kg seed, or carboxin 37.5 + thiram 37.5 WS at 3 g/kg
  • Cultural: timely October-November sowing in NWPZ; avoid late sowing into foggy December; remove and burn crop debris immediately after harvest; rotate with cereals for 2-3 years on heavily infested fields; avoid dense plant population (keep 30 x 10 cm spacing)
  • Foliar fungicides at first symptom: mancozeb 75 WP at 2.5 kg/ha, chlorothalonil 75 WP at 2 kg/ha, or propiconazole 25 EC at 500 ml/ha; repeat at 10-15 day intervals during cool-humid spells; pre-flowering preventive spray of mancozeb is standard ICAR-IIPR recommendation in NWPZ

The combined package — resistant variety + seed treatment + timely sowing + 1-2 preventive sprays — keeps losses below 10% in most years.

See also: Bengalgram crop, KAK-2 kabuli, Himachal Bharat kabuli, Chickpea fusarium wilt, Chickpea dry root rot.

Sources

  1. Ascochyta blight of chickpea — management. ICAR-Indian Institute of Pulses Research, Kanpur.
  2. Ascochyta blight. ICARDA chickpea programme.
  3. Ascochyta rabiei factsheet. CABI Plantwise.