Fusarium wilt

C/O: Fusarium oxysporium f.sp. vasinfectum

Etiology:

• The macro conidia are 1-5 sepatae, hyaline, thin walled, linear to falcate.
• The tapering micro conidia are hyaline, thin elliptical to spherical , single or two celled.
• Also produces chlamydospores ( dark and thicken )
• Inter and intracellular growth.

Symptoms:

• Disease starts at the age of 1-3 weeks.
• Yellowing and browning of the cotyledons.
• Leaves lose their turgidity.
• First turn yellow and then brown and finally drop off.
• The tap root ceased to grow, and less no. of lateral roots emerged.
• Browning and blackening of vascular tissues.
• Discolorations of leaves starts from the margins and spread towards midribs.
• Wilting may be complete(tap root infection) or partial (lateral root infection).
• Young plants lower part becomes black whereas partial discoloration is observed in case of mature plants.
• The plugged xylem vessels of blackish color is observed under examination.
• The vascular bundles with fungal hyphae and gummy substances can be observed with transverse section cut.

Favorable condition:

• Hot and dry periods followed by rains.
• Heavy black soils with an alkaline reaction.
• Increased doses of nitrogen and phosphatic fertilizers.
• Wide range of temperature; 10 to 35°C but grows well at 18- 27°C.
• Humidity: > 75%
• Soil pH=5.3

Disease cycle:

• Fusarium is soil and externally – internal seed born pathogen.
• Resting stage: chlamydospore
• Primary inoculum: chlamydospore, hyphae
• Secondary inoculum: micro and macro conidia or air borne conidia
• Transmission: air, water

Management

• Management of crop debris.
• Deep ploughing during hot sunny days.
• Apply increased doses of potash with a balanced dose of nitrogenous and phosphatic fertilizers.

• Use of resistance cotton varieties like Gossypium hirsutum
• Intercropping with sorghum : root of sorghum exudates HCN which isphytotoxic to fusarium.
• Mix cropping to keep the temperature below 20°C.
• Seed treatment with Bavistin 2gm/kg of seed.
• Spot drench with Carbendazim 1g/litre.