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

Practical - 10

Exercise: To Study the Symptoms Produced by Nematodes.
Definition: Visible expression or indication of any infection/disease is called symptom.
Why study Symptoms?

• Symptoms are very important for diagnosis of a disease and management practices can be undertaken only when the correct information about the disease and its etiology is available.

1. Non specific above ground symptoms
A. Patches of stunted plants in nursery/field: Nematode infestation initiates in field in form of patches of retarded , weak and chlorotic plants.

Patchy growth in tomato and Patchy growth in okra due to root-knot nematode

B. Chlorosis (discoloration, yellowing, bronzing, intervenal discoloration etc.): Non specific yellowing is the common symptom of nematode attack but some nematodes like Aphelenchoides ritzemabosi and A. fragariae cause specific reddening and bronzing on host plants

Yellow, stunted patches in ginger due to Pratylenchus Zeae and Yellow, stunted patches in carnation due to root-knot nematode

C. Temporary Wilting: Nematode infested plants show signs of wilting during hot sunny hours from which they recover during cooler parts of the day. Broad leaved plants are more prone to wilting.

Wilting in tomato and Wilting in Capsicum Specific above Ground Symptoms:

I. Crinkling and foliage distortion: Foliage of plants belonging to Family Graminae often gets crinkled and distorted when infested with foliar nematodes like Anguina spp. , Ditylenchus angustus and Aphelenchoides besseyi

Healthy and crinkled wheat ears; crinkling due to Anguina tritici and Rice panicles distorted due to Aphelenchoides besseyi Photo by: Jonathan D Eisenback,NemaPix

II. Seed galls: Black shrunken galls at the place of normal wheat seeds are produced by Anguina tritici.

Healthy wheat grains and Black shrunken galls(due to Anguina tritici) Photo by: Ulriche Zunke NemaPix

2. Non specific below ground symptoms
A. Reduced root system
Depletion of root system is the common symptom of nematode attack but the way in which a reduced system occurs, varies from species to species.

Reduced root system in Carnation roots pruned due to root-knot nematode

Stubby corn roots due to feeding by Trichodorus sp.

4. Specific Below ground symptoms

• Root lesions: Root lesions are the discoloured and often collapsed portion of the root consisting of cells on which nematodes have already fed.

Primarily burrowing and lesion nematodes produce lesions on roots.

• Root rots: When nematodes enter the fleshy structure and feed, in the process they cause decaying of the tissue. When other plant pathogens like bacteria or fungi enter through this decayed tissue, rotting occurs.

 

The potato rot nematode Ditylenchus destructor is involved in this type of injury.

Tuber rot caused by D. destructor

2. Root Proliferation (Root Sprangling)
The formation of numerous small roots at the expense of more deeply penetrating larger roots is called sprangling. It renders the plants more susceptible to wilting and these plants are easily uprooted and their ability to absorb nutrients is also impaired.
Meloidogyne hapla causes excessive branching in tomato. Sprangling on crops such as carrots and turnips, render them unmarketable.

Root proliferation in summer squash

Root knots or Root galls
The abnormal galling or swelling of the roots is a specific diagnostic symptom of nematode infestation.
Meloidogyne spp. produce characteristic galls on the roots and host plants.

The size and number of galls vary from species to species and host to host.

• While woody plants like cotton and carnation show small galls, very large galls are produced on cucurbits which may coalesce with each other in a way that the entire root looks swollen and deformed.
• Extensive galling is often observed on crops like tomato, okra, brinjal etc.

Extensive galling of okra roots and Heavily galled cucurbit roots

Heavy galling in tomato seedlings under nursery conditions and Small galls produced on carnation roots

Cysts on Roots

• Pearly white swollen cysts (dead females) are often observed adhering to the root which can be observed easily by careful examination with a magnifying glass.