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

Under Ground Symptoms

The common symptoms shown on below ground parts of the plants suffering from nematode infestation are:

1. Reduced root system and injured root tips
2. Root lesions
3. Root rots
4. Root Proliferation (Root Sprangling)
5. Root knots or Root galls
6. Cysts on roots

1. Reduced root system and injured root tips
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

• Tylenchorhynchus claytoni and Trichodorus spp. apparently inhibit root growth without any other recognizible symptom.
• Coarse roots are produced by Belonolaimus longicaudatus on corn. The growth of lateral roots is stopped just as most of them are breaking through the cortex or while they are very short, an open root system consisting of main roots largely but devoid of small branch rootlets. Sugarcane infested with Tylenchorhynchus and Pratylenchus spp. and citrus infested with Radopholus similis shows such symptoms.
• Curly tip of roots of seedless grapes is specifically produced due to infestation of Xiphinema index.
• Injured root tips may be caused by the nematodes feeding on or near the root tips and may cause them to stop growing and die. Short stubby and malformed roots are caused in this case. e.g. corn affected by Trichodorus christiei and sugarcane infested with Tylenchorhynchus etc. The branch rootlets manage to attain a moderate length before their growth is stopped. The resulting root system has numerous, short stubby branches, often arranged in clusters.

 

Short stubby corn roots due to Trichodorus sp.

2. 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 dead areas on roots.
• They vary in size from a few cells to the lesions girding the whole root. Primarily ring nematodes (Criconemoides spp.) generally produce only small lesions. Radopholus similis causes big lesions on banana roots.
  

Root lesions on banana root caused by Radopholus similis

3. Root rots

• When nematodes enter the fleshy structure, they initiate the injury leading to the extensive tissue destruction. Through the decayed tissue, the other plant pathogens like bacteria or fungi may attack and as a result rot is produced.
• The potato rot nematode Ditylenchus destructor is involved in this type of injury (so far not reported from India).

Tuber rot caused by D. destructor

4. Root Proliferation (Root Sprangling)
Some species of nematodes do not produce root decay or lesions but numerous short lateral roots may form in the vicinity of nematode injury causing excessive root branching or a hairy root condition. The formation of such numerous small roots at the expense of more deeply penetrating larger roots often renders the plants more susceptible to wilting and these plants are easily uprooted and their ability to absorb nutrients is also impaired.

• This effect is often caused by cyst nematodes (Heterodera avenae on oats, H. glycines on soybean, H. schachtii on sugarbeet and Globodera rostochiensis on potato). Meloidogyne hapla causes excessive branching in tomato. Sprangling on crops such as carrots and turnips, render them unmarketable. .

Fig 9.5a: Root proliferation of beet root by H. schachtii  ig. 9.5 Root proliferation in summer squash
Photo by Stephen Lewis, Nemapix Vol. 3