1. 
Factors Influencing Nematode Population and
Distribution

2. 
 The spectrum of nematode population at a given
point of time is the result of interactive ambient
abiotic & biotic factors.

3. 
Abiotic Factors Biotic Factors
 Temperature  Host plants
 Moisture & aeration  Micro-organisms
 Texture
 Chemicals
 pH

4. Abiotic Factors

 Most plant parasitic nematodes spend their entire
life cycle in soil. Even those nematodes which enter
plant tissues including forms parasitizing aboue
ground plant parts, spend atleast part of their life
cycle in soil.

5. Soil Temperature

 Most plant parasitic nematodes have optimum
thermal requirements between 15-30o C. Nematodes
are able to survive a lower temperature limit of 5o C
& upper limit 40o C, but further extremes of lower &
upper limits may be lethal.
 Ex: Meloidogyne javanica may by completed in 25-30
days at 30o C, but same may be extend to 90 days at
15-20o C.

6. Soil Moisture & Aeration

 Agricultural soils are beset with wide flactuations in
soil moisture.
 Soil aeration is inversely related to moisture content.
 Nematodes require a thin film of water for their
biological activities.
 Excessive moisture tends to inhibit the locomotion of
nematodes in soil.

7. 
 Lack of oxygen in saturated soil also adversely
affects nematode population due to asphyxia.
 Ex: Hirschmanniella spp thrive well in flooded soils of
rice field.

8. Soil Texture

 The relative proportion of sand, silt & clay
determines the soil texture.
 Certain nematodes prove more pathogenic in light
textured soil.
 Ex: Heterodera avenae on wheat & barley.
 Rotylechulus reniformis thrive well in fine & medium
textured soils.

9. Soil Chemicals

 The concentration of chemical constituents of soil
flactuates drastically depending upon soil moisture
content (irrigation, drought). The use of chemical
fertilizer, organic manures, pesticide etc. further
adds to the dynamism of soil chemistry.

10. Soil pH

 pH does not affect the nematodes directly. They can
exist with in normal pH range (4-8) of agricultural
soils, provided it safe for host plant growth.

11. Biotic Factor
Host plants

 Crops & cropping pattern influence plant parasitic
nematode populations tremendously.
 Some nematodes have wide host ranges while others
parasitize only selected hosts.
 The status of host is highly variable.
 The multiplication rate of nematode species may be
very high on a plant species (good host),while some
other plant species (poor host) may not be very
favourable for multiplication.

12. Micro-organism

 Soil micro-oraganisms in the rhizosphere influence
nematodes in various ways.
 The nature of damage by nematodes to plants may
be drastically influenced by other plant pathogenic
organisms (fungi, bacteria, virus) present in
rhizosphere.
 Nematodes actively interact with these organisms
resulting in disease complexes which are common
places in nature.

13. Distribution

 The locomotion of nematodes per se is very limited.
 They can hardly move a few cm in a year by their
own movement.
 They can spread by various means.
 Short distance spread is usually facilitated by
irrigation, agricultural machinery, wind, livestock
etc.,
 Long distance occurs through plant propagating
material, seedlings, saplings etc.,

14. 
Take care of crops from deadly
nematodes…