The most significant Nematode species on agricultural crops
"Definition of nematodes"
The word nematode was originally derived from two Greek words: nema, meaning: thread, and eidos, meaning: similar.
Accordingly, these organisms were known as nematodes, but they are now known as nematodes, or for short, nematodes, and sometimes they are called snake worms, but this name is inappropriate.
The latter is not entirely correct, because not all nematodes have serpentine movement.
Nematodes are invertebrate (primitive) cylindrical worms, and they are considered mainly aquatic animals that live in salt or fresh water, or at least their bodies must be covered by a thin membrane of water in the soil in order to be alive and active.
Nematodes are found in capillary water around soil grains and nematodes are widespread as they can be found in any environment where the reasons for life are available.
They are found in dry desert lands, in polar regions, in hot spring waters, as well as in the depths of the oceans.
Opinion has finally settled on placing it in an independent division (tribe) within the animal kingdom, which is the Phylum Nematode division (tribe), due to the increased interest in studying it, especially as an agricultural pest. This phylum is considered one of the largest multicellular animal groups after the insect group, especially in terms of density and diversity.
Morphological features of nematodes:
Its body is cylindrical and transparent.
Spindly or filamentous bodies are possible.
Some females of some sexes may swell and take different shapes (globular-lemon-pear-renal).
Its size ranges from 0.4 to 4 mm.
Parasitic species on plants are not more than 1 mm long and may reach 4 mm.
The width of the nematodes is no more than 15-20 microns, and the average length of these worms is between 3-6 mm.
It is also not visible to the naked eye, and its body is transparent, as it does not contain colored pigments.
One drop of water may contain several thousand (8000) nematodes.
The life cycle of nematodes
It takes 30-45 days in temperatures ranging from 25 to 30 degrees Celsius.
The life cycle is long in winter and reaches 60-90 days.
It comes to a halt if the temperature falls below 12 degrees Celsius.
Females lay eggs (singly or in clumps) within plant tissues or in the soil.
egg-first age caterpillar-second age caterpillar-third age caterpillar-fourth age caterpillar-whole animal.
The infective stage in most species of nematodes is the second larval stage.
The number of generations depends on the type of nematode:
Root knot nematodes (7–10 generations).
Renal nematodes (6–8 generations).
Citrus nematodes (4-5) generations take from 30-45 days at a temperature of 25–30 m.
Means of transmission and spread of nematodes
- Transfer of agricultural soil contaminated with nematodes.
- Use of compost contaminated with soil residues and infected roots.
- Infected seedlings, seeds, and bulbs.
- Humans and animals.
- Remains and residues of infected plants (roots).
- Agricultural machinery (plow).
- Irrigation water, especially in the case of surface irrigation.
How do nematodes feed on plants?
Nematodes that feed on plants have needle-like spears that are 12–100 microns long. Nematodes feed on plants by piercing the plant cell walls with this spear, secreting enzymes, and then sucking up the contents of the cell.
The ability to absorb also occurs as a result of contraction in the esophageal muscle.
Totals of nematodes present in the soil:
1-Replenished nematodes.
2- Predatory nematode.-
3- Plant parasitic nematodes: They are the ones that interest us in this field. The root-knot nematodes and citrus nematodes are two of the most well-known species in this group, which is found throughout Egypt. There are two types of nutrition in nematodes parasitic on plants:
- external intrusion.
- semi-indoor intrusive (internal static-internal roving).
- internal snooping.
- Ulcers or tumors and knots on the roots.
- Yellowing, wilting, and distortion of roots and plants.
- Plants are stunted and, in some cases, completely collapse.
- It also affects the size and quality of the crop.
- Determine the agricultural cycle.
- The presence of these nematode pests in large numbers causes crop cycle designers to be limited to a certain number of crops.
- limiting the use of agricultural fertilizers to increase natural enemies and decrease the number of pests, such as superphosphate and urea.
- Conducting many agricultural transactions aimed at eliminating pests, such as the use of pesticides or agricultural methods that may result in land flooding or waste, adds expenses to the cost of production.
- When the pest population reaches an epidemic level, the land loses its productive value as it affects the productivity of the plant due to its lack of elements, so it is called "soil sick."
- Pests lead to a decrease in soil fertility as nematodes may eat the nitrogen-fixing bacteria in the soil.
Factors on which nematode damage depends
The type of the crop or the plant itself (sensitive-resistant-tolerant).
type of nematode.
Infestation size and nematode numbers.
Other environmental factors:
soil temperature and moisture.
Soil pH.
Soil microorganisms.
The most serious nematode diseases:
- Nematodes infect the shoots:
1-Leaf nematodes such as Aphelenchoides spp.
2-Market and bulbous nematodes such as Ditylenchus spp.
3-Seeded nematodes (for example, Anguina tritic).
- Nematodes infect the root system.
1-External parasites such as Tylenchorhenchus
2-Endoparasites such as Tylenchulus semipenetrans - Rotylenchulus reniformis.
3-Semi-indoor parasitoids ( Meloidogyne spp., Pratylenchus).
- The most significant nematode species on agricultural crops
1- Soybean cyst nematode (SCN)
Symptoms
Disease control
2-Root-knot disease
Cause: Root knot nematode
Importance and distribution: Various species of the genus Eloidogyne M cause root-knot disease on thousands of plants worldwide.
The root knot nematode is the most important plant nematode and it is one of the most prevalent species in many vegetable crops (tomatoes, cucumbers, potatoes, cucurbits, legumes), fruits (grapes, peaches, figs, olives, bananas, pomegranates) and field crops.
On sandy and light lands, the loss as a result of infection may exceed the loss of the entire crop, and it is considered a parasitic and dormant internal nematode.
Species: The following four species are M. arenaria, M. hapla, M. javanica, and M. incognita. They are the main and most common species in agricultural lands, as they constitute more than 95% of the species of root-knot nematodes in agricultural lands in the world.
3-Citrus slow decline disease
Cause: Citrus nematode
Importance and spread:
Citrus nematode is the name given to one species, T. semipentrans, but these nematodes appear to have developed strains that can reproduce on plants other than citrus, such as olives, grapes, and mangoes.
Symptoms of infection:
Nematodes feed on the cortex area of the root of the host, and through continuous feeding, cells die, ulcers appear, and tissue dies on the roots. They are dark brown and stick to the soil granules strongly due to the gelatinous substance in which the female lays her eggs. In the case of severe infection, the cortex is separated from the cylinder. Symptoms of yellowing, wilting, and a decrease in the yield of the affected trees also appear.
4- Renal nematode disease
Cause: -renal nematode
Importance and spread:
The renal nematode and citrus nematode constitute the two most important genera of semi-endogenous feeding nematodes, and about 65 species of the genus Rotylenchulus are known so far, but the most famous and most widespread is the type R. Grapes, jasmine, soybeans, tomatoes, bananas.
Symptoms of infection:
Infected trees and seedlings are weak and stunted, and by examining the roots, ulcers are noted in the epidermal layer and bark, and in the case of severe infection, the crust layer separates from the vascular cylinder. Other organisms entering the infestation increase the effect of the nematode and accelerate the decomposition of the affected tissue.
5- canker sore disease
Cause: -root canker nematode
Importance and spread:
The canker nematode Pratylenchus spp. It is one of the most important genera of nematodes that parasitizes and wanders inside the endo-migratory roots and is spread almost all over the world.
It is considered, with its severe canker sores on the roots, responsible for the deterioration of the root system of infected seedlings and trees, which leads to a significant decrease in vegetative growth and production.
Among the most important crops that affect it are (peach-pear-strawberry-potato-apple-banana-citrus-peanuts-olives-cotton-cowpea-peas-tomatoes-alfalfa-beets).
Species:
More than 166 species belong to the Pratylenchus genus, most of which are roving endoparasites. The most important and most widespread species are P.penetrans, P.brachyurus, P.zeae, P. vulnus, and P. coffeae. Penetrans Pratylenchus is the most common species, followed by P. vulnus.
Symptoms of infection:
Infected trees show general symptoms such as weak plants, dwarfing and yellowing of their leaves. These symptoms also appear in the field in the form of groups of plants in scattered spots according to the severity of the infection.
There are also symptoms on the affected roots, such as the presence of dark brown ulcers scattered along the root caused by the oxidizing phenols that are produced by the parasitism nematode and cause the death of many cells of the cortex and may separate from the vascular cylinder.
Cause: -renal nematode
Importance and spread: The renal nematode and citrus nematode constitute the two most important genera of semi-endogenous feeding nematodes, and about 65 species of the genus Rotylenchulus are known so far, but the most famous and most widespread is the type R. Grapes, jasmine, soybeans, tomatoes, bananas.
Symptoms of infection:
Infected trees and seedlings are weak and stunted, and by examining the roots, ulcers are noted in the epidermal layer and bark, and in the case of severe infection, the crust layer separates from the vascular cylinder. Other organisms entering the infestation increase the effect of the nematode and accelerate the decomposition of the affected tissue.
