Diseases of Vegetable, Ornamental and Spice Crops (2+1)

FUNGAL DISEASES

1. WILT

The disease is considered as one of the most damaging disease of this crop and cause considerable yield losses.

Symptoms:

• The characteristics symptoms of the disease include drooping of the leaves, marginal yellowing and rotting of the roots or rootlets.

Pathogen:

• The disease is caused by Rhizoctonia sp. and Fusarium solani (Mart.) Sacc.
• The mycelium of Rhizoctonia sp. is septate, brownish, dolipore type, 5-14 µm wide.
• The lateral branches of the mycelium are constricted at branching point and possess septum near the junction.
• The sclerotia are small and brown to black in colour.
• F. solani mycelium is septate and produces microconidia, macroconidia and chlamydospores.

Disease cycle and epidemiology:

• These fungi overwinter in the infected plant debris as well as in soil as sclerotia or chlamydospores.
• Moderate to high temperatures with fair amount of moisture was found conducive for disease development.
• The infection is more severe if the nematode (Pratylenchus sp.) predisposes the plant for the attack of the pathogens.

Management:

• Collect and destroy the infected plant debris to reduce the primary inoculum.
• Follow long crop rotation.
• Soil amendment with neem cake (250g/m2) and soil solarization for 40-45 days during summer months are also helpful in managing this disease.
• Drenching of soil with carbendazim (0.1%) or thiophanate methyl (0.1%) immediately after appearance of the symptoms gave good control.

2. BOTRYTIS SPOT AND BLIGHT:
Symptoms:

• The disease appears during the rainy season.
• Infected flowers show dark brown spots.
• In favourable weather, the disease assumes serious proportions and entire inflorescence dries up. The infection occurs on the leaves and stalks.

Pathogen:

• The fungus responsible for this disease is Botrytis elliptica (Berk.) Cook.
• Branched conidiophore bear conidia which are aseptate, hyaline, botryos, mostly 20-30 x 13-18 µm in size
• Sclerotia are sometimes forms

Epidemiology:

• Pathogen perennates either in the form of mycelium or sclerotia in the infected plant debris.
• Warm and humid weather is favourable for this disease.

Management:

• Collect and destroy the infected plant debris.
• With the initiation of the disease, spray the crop with carbendazim (0.1%) and repeat at 10 to 14 days interval.

3. SCLEROTIUM WILT
Symptoms:

• The initial symptoms of the disease appear as flaccidity and drooping of leaves which ultimately become yellow and finally dry up.
• The fungus mainly affects the roots and collar portion of the stem.
• Both tubers and roots show wilting symptoms.
• Thick cottony growth of the fungus is visible on the rotten stem and petioles at soil level.

Pathogen:

• The disease is caused by Sclerotium rolfsii Sacc.
• The fungus consists of coarse hyphae and the size of cells ranges from 150-250 µm x 2-9 µm.
• The hyphae of this fungus pathogen are characterized by the presence of clamp connections and a peculiar method of branching, which are valuable aids in ascertaining its taxonomic position.
• The sclerotia (0.5-1.5 mm in dia.) at first white but becoming brown with age are more or less smooth and glossy and somewhat resemble mustard seed.

Disease cycle and Epidemiology:

• The fungus overwinters in the form of sclerotia in soil.
• Warm and humid climatic conditions favour this disease.

Management:

• Cultural practices like crop rotation, collection and destruction of infected plant parts and soil solarization for atleast 45 days should be followed during summer months.
• Drench the soil with zineb (0.3%) and repeat at 10 to 14 days interval.