Species complex
i) Meloidogyne arenaria (Neal) Chitwood
ii) M. hapla Chitwood
iii) M. incognita (Kofoid & White) Chitwood
iv) M. javanica (Kofoid & White) Chitwood
Distribution: Root knot nematodes are world- wide in distribution. In India they are distributed as follows:
Meloidogyne arenaria - Plains
M. hapla - Hills
M. incognita - Certain pockets in hills and plains
M. javanica - Mid hills and plains of India
Host Range: Polyphagous.
Nature of damage and symptoms:
Hindrance
in normal functions of nutrient and water uptake/ translocation.
Infested
plants are dwarfed, chlorotic and have poor root development. 
There
is 42.5 % yield reduction upon 100 % tuber infestation.
Life cycle:
· The 2nd stage juveniles hatch from the eggs and first infest the young roots (Fig).
· They form giant cells through which the nematodes extract nourishment from the plant cells.
· Later on the giant cell and development of nematode within the roots results in the formation of root-knots or galls.
· The female larvae gradually enlarge and undergo four moults before forming a pear shaped structure.
· The male nematodes, however, retain their thread like appearance.
· Males come out freely from the root system and mate with females to fertilize the eggs.
· The female are sedentary depositing 300 to 400 eggs into a gelatinous matrix usually adhering to the root galls. These eggs hatch readily and invade the fresh roots.
· In Shimla hills, M. incognita completes its life cycle in 25-30 days during summer (April-September) but takes about 65 to 100 days in winter (October-March).
· In the hills normally two generations are completed by the time of tuberization.
· On the other hand, tuber infestation in plains remains low mainly because the crop duration is short and fresh roots are not always available.
· Further, hot summers in plains reduce the soil populations of RKNs.
· The eggs and larvae can survive for more than 100 days even in the absence of the hosts during summer months at Shimla hills.
· This could be one of the reasons for continuation of higher inoculum levels causing higher infestation in subsequent crops.
Life cycle of root knot nematode (RKN).
Management:
· Deep ploughing and sun drying of fields during summer months help in drying of infective stages of larvae.
· Planting of potato crop during the 2nd week of October in autumn and in early January for the spring can limit RKN infestation on tubers.
· Burning of trash in field before planting helps not only by sterilizing the soil but also enriching it, though possible only for small holdings.
· Growing one row of trap plants like Tagetes patula and T. erecta (African marigold) in between 2 or 3 rows of potatoes improves the crop performance by reducing RKN infestation.
· RKN being polyphagous in nature, having a wide host range yet a few crops are free from M. incognita infestation allowing crop rotation with a non-host, like maize, wheat, millets, beans etc. for reducing RKN infestation.
· Potatoes harvested from RKN infested field should not be used as seed for subsequent crop. Movement of the soil and water from infested fields to RKNs free fields should also be avoided. Besides, the field should be kept free from weeds as RKNs have a wide host range and most of the weeds help them.
· Amendment of de-oiled cakes of neem, groundnut, sesamum, castor, mahua and karanj etc. are known potential examples to minimize root-knot nematodes populations and losses caused by them.
· An effective control of RKN can be achieved either through Carbofuran 3G @ 75 kg a.i. or Aldicarb @ 2 kg ai/ha preferably in two equal splits i.e. half at planting and remaining half at earthing time.