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Ginger soft rot (Pythium aphanidermatum) Photo: placeholder pending image-fill pass

Ginger soft rot (Pythium aphanidermatum)

Soft rot, also called rhizome rot, is the most destructive disease of cultivated ginger (Zingiber officinale) in India. It is caused mainly by the soil-borne oomycete Pythium aphanidermatum with secondary association of P. myriotylum, P. ultimum and the bacterium Pseudomonas solanacearum. Crop losses of 50-90% are reported when the disease establishes in poorly drained or recycled ginger plots.

Identification and symptoms

The first visible symptom is water-soaked yellowing at the collar region of the pseudostem. The pseudostem then becomes pale yellow, slips off easily on a slight pull and emits a foul odour. Below ground the rhizome turns watery, soft and mushy, with the cortex sloughing away when pressed. Lower leaves yellow and dry upward; the entire clump can collapse within 1-2 weeks. In wet conditions a white cottony mycelium is visible on infected tissue.

Hosts and life cycle

Pythium aphanidermatum survives in soil as oospores and as mycelium on crop debris for several seasons. Infection is initiated through wounds on the seed rhizome at planting and through pseudostem base in standing crop. Optimum infection occurs at 28-32 °C with continuous soil moisture and waterlogging following heavy rain. The pathogen has a wide host range including turmeric (Curcuma longa), cucurbits, brinjal and tomato, all of which can carry inoculum on the same plot.

Damage and economic impact

Soft rot is the single largest cause of yield loss in Indian ginger; in continuously cropped plots in Kerala, Karnataka, Meghalaya, Mizoram and Sikkim losses of 30-90% are routine. The bulk of "yield gap" between the traditional [[ginger-maran-nadia-traditional|Maran and Nadia cultivars]] and demonstration plots is attributable to soft rot.

Management

ICAR-IISR Calicut and the Spices Board recommend an integrated package:

  • Crop rotation: minimum 3-4 year rotation with non-host crops (cereals, legumes); avoid back-to-back planting on the same plot.
  • Site and seed: well-drained sloping land; raised beds 30 cm high with surface and side drainage. Select bold healthy mother rhizomes from disease-free plots.
  • Seed treatment: dip seed rhizomes in mancozeb 0.3% + streptocycline 200 ppm for 30 minutes, shade dry before planting; alternatively Trichoderma harzianum slurry @ 10 g/kg seed.
  • Soil drench: apply Trichoderma viride (IISR strain) @ 4 kg/ha enriched on FYM at planting and at earthing-up. Drench affected patches with mancozeb 0.3% or copper oxychloride 0.2%.
  • Sanitation: rogue out wilting clumps with surrounding soil and destroy. Provide drainage immediately after heavy rain.
  • Tolerant ICAR-IISR releases (IISR Mahima, IISR Rejatha, IISR Varada) carry partial field resistance.

See also: Ginger Crop, Ginger Maran Nadia Traditional, Turmeric Crop.

References

  1. Soft rot of ginger - ICAR-IISR Calicut. https://www.spices.res.in/research/ginger
  2. Ginger diseases management - Spices Board India. https://www.indianspices.com/spice-catalog/ginger