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Sigatoka leaf spot complex of banana Photo: placeholder pending image-fill pass

Sigatoka leaf spot complex of banana

The Sigatoka leaf spot complex consists of two closely related fungal diseases of banana: yellow Sigatoka caused by Mycosphaerella musicola (anamorph Pseudocercospora musae) and black Sigatoka (or black leaf streak) caused by the more virulent Mycosphaerella fijiensis (anamorph Pseudocercospora fijiensis). Yellow Sigatoka is endemic across all major banana-growing states; black Sigatoka has been reported from north-eastern India and pockets of Kerala. ICAR-NRCB Trichy operates a national disease-monitoring network for both pathogens.

Identification and symptoms

Yellow Sigatoka first appears as pale-yellow streaks on the upper leaf surface that elongate parallel to the veins, then darken to oval brown spots with a grey centre and yellow halo. Black Sigatoka begins as fine reddish-brown specks on the lower leaf surface, expanding into black streaks and coalescing into large necrotic patches. In both diseases the youngest functional leaves are progressively destroyed, reducing photosynthetic area, advancing fruit maturity prematurely and producing bunches with poor finger filling.

Host crops and life cycle

Both pathogens infect all commercial cultivars including Grand Naine (Banana Grand Naine G9 Jain Tc, Banana G9 Tissue Culture), Nendran (Banana Nendran Kerala Plantain) and Poovan (Banana Poovan Mysore Tn). The fungi produce both ascospores (rain-dispersed, long-distance) and conidia (rain-splash, short-distance). Warm, humid conditions (24-28 °C, >90% relative humidity, frequent rainfall) are highly conducive; black Sigatoka has a shorter latent period and is more aggressive than yellow Sigatoka.

Damage and economic impact

Uncontrolled Sigatoka can reduce bunch weight by 30-50% and shorten the green-life of harvested fruit, undermining export potential. Black Sigatoka, where present, can render Cavendish plantings uneconomic without intensive fungicide programmes.

Management

ICAR-NRCB recommends an integrated package:

  • Cultural: removal and destruction of severely affected leaves (de-leafing); wider spacing for air circulation; mat sanitation; sucker management to maintain three healthy leaves per plant at flowering.
  • Resistant material: deployment of relatively tolerant selections under evaluation; tissue-cultured plants of less-affected cultivars.
  • Chemical: alternation of protectant fungicides (mancozeb 0.25%, chlorothalonil) with systemic triazoles (propiconazole 0.1%, difenoconazole, tebuconazole) and strobilurins (azoxystrobin); spray oils improve coverage and persistence.
  • Decision support: forecasting based on biological- and disease-severity-state systems; treatment thresholds rather than calendar sprays.
  • Stewardship: rotation of fungicide modes of action to slow resistance development, which has been documented in black Sigatoka populations elsewhere.

See also: Banana Grand Naine G9 Jain Tc, Banana Bunchy Top Virus, Banana Fusarium Wilt Foc Tr4, Banana Nendran Kerala Plantain, Banana G9 Tissue Culture.

References

  1. Sigatoka leaf spot management. ICAR-National Research Centre for Banana, Trichy.
  2. Leaf spot diseases of banana. ICAR-Indian Institute of Horticultural Research, Bengaluru.