Diseases of Vegetable, Ornamental and Spice Crops

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.