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Citrus gummosis (Phytophthora)

Citrus gummosis, locally called dinkya in central India, is a soilborne disease of citrus caused by Phytophthora species (chiefly P. nicotianae and P. palmivora). It is the principal disease constraint in Nagpur mandarin and Mosambi orchards of the Vidarbha-Marathwada region and is reported to kill 2-3 lakh citrus trees annually in Vidarbha alone.

Identification and symptoms

Affected trees ooze sticky, amber-coloured gum from cracks in the lower trunk and crown region. Bark beneath the lesion turns dark, becomes water-soaked and eventually sloughs, girdling the trunk. Symptoms above ground are accompanied by feeder-root rot and progressive yellowing and shedding of leaves; severely affected trees collapse within one or two seasons.

Host crops and life cycle

The pathogen survives in soil and infected plant debris as oospores and chlamydospores, and produces motile zoospores in free water. Infection is favoured by waterlogged soils, deep planting that buries the bud union, mechanical injuries and warm wet weather following pre-monsoon showers. Mosambi (Citrus Mosambi Sweet Lime) and Nagpur mandarin are both highly susceptible; lime and lemon are relatively more tolerant.

Damage and economic impact

Beyond direct tree death, gummosis shortens the productive life of an orchard, reduces yield in surviving trees and forces frequent replanting. Vidarbha extension agencies report cumulative annual losses of the order of 2-3 lakh trees in the citrus belt. Dense plantings without adequate air movement aggravate the disease (Citrus Spacing Canopy Collapse).

Management

ICAR-CCRI Nagpur and NHB advisories recommend an integrated approach:

  • Cultural: avoid deep planting (keep the bud union 15-20 cm above soil), provide raised mounds and field drainage, and remove infected bark.
  • Biological: pre-monsoon soil application of Trichoderma harzianum / T. viride at around 1 kg/tree mixed with farmyard manure.
  • Chemical: bark scraping followed by paint with Bordeaux paste or mefenoxam-MZ paste; foliar/soil drench of metalaxyl-MZ (Ridomil) at about 2.5 g/L during outbreaks.

See also: Citrus Mosambi Sweet Lime, Citrus Spacing Canopy Collapse.

References

  1. Foot Rot or Gummosis. National Horticulture Board.
  2. Integrated disease management for root rot and gummosis in Nagpur mandarin. ResearchGate.