Nematode Pests of Horticultural Crops and their Management (1+1)

Chrysanthemum

I. Chrysanthemum
Large areas in the states of Karnataka, Tamilnadu, Madhya Pradesh and Bihar are under chrysanthemum cultivation. Nematodes of major significance in chrysanthemum are Aphelenchoides ritzemabosi and Pratylenchus coffeae.

a. Chrysanthemum foliar nematode (Aphelenchoides ritzemabosi)

Nature of Damage:

• It is an above ground migratory parasite that feeds upon mesophyll tissue of leaf and growing buds as a result of which the tissue becomes necrotic.
• Nematodes overwinter in dead, infested leaves on the ground or between the scales of infected buds.
• In the spring, the nematodes become active and swim up the plant stems.

Symptoms:

• The symptoms produced on chrysanthemum leaves are fairly characteristic.
• Initially, small yellow spots are visible between the large veins which turn brown with age. They also coalesce as the feeding continues and a large V-shaped angular area of necrotic tissue is formed.
• Eventually the entire leaf turns brown, becomes brittle, and is shed.
• Leaves arising from infected buds are distorted and smaller than normal.
• Their petioles and the stem tissue around the buds contain brown scars when nematode feeding destroys the cells.
• Nematodes may also feed on ray flowers and impede their normal development.
• Secretions from A. ritzemabosi cause shortening of internodes (rosetting) giving a bushy appearance to theaffected plants.Other symptoms caused by nematode secretions include production of low, premature side shoots and distorted leaves.
• A condition called blindness also occurs on infested plants. It is characterized by shoot browning and failure to grow.
• In the most severe cases plants die after producing a limited amount of normal foliage and marketable flowers.
• The disease tends to progress from the lower to the upper leaves as the nematode moves up the plant.
• While symptoms may be dramatic and readily visible, it is important to note that plants may survive as symptomless carriers. These plants can support a high number of nematodes and exhibit few, if any, visible symptoms.

Fif. 15.1 Damage caused by foliar nematode on chrysanthemum
Source:Forestryimage,org

Management

• Sanitation. Remove infected plants and debris in the fall and destroy it. Remove individual infected lower leaves from the plant before the nematode moves upward.
• Healthy propagation. Take cuttings from the upper portion of the plant. Disinfect dormant cuttings and stools with a hot water treatment (50o C for 5 min or 44o C for 30 min)
• Cultural Practices. Use a heavy layer of mulch over fallen leaves in ornamental plantings to prevent upward movement of the nematode. Avoid overhead irrigation and time irrigation to limit the foliage remaining wet. Space plants to allow good air flow and rapid drying.
• Chemical Control. Thionazin drench @ 0.2% twice in a fortnight is advisable in commercial cultivation.

b. Root lesion nematodes (Pratylenchus spp.)

 

• At least three species viz., Pratylenchus coffeae, P. chrysanthus and P. fallax have been recorded to be associated with chrysanthemum.
• These nematodes are responsible for extensive cortical lesions on the roots due to intra as well as inter cellular movement of the nematode in the root tissue that eventually leads to stunted growth of plants, premature yellowing and drying of leaves.