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.
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.
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.
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.
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.
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.
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.
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.
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.
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.,