Plant Damage by Sedentary Root Nematodes
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| License | No Open Access License: German copyright law applies. This film may be used for your own use but it may not be distributed via the internet or passed on to external parties. | |
| Identifiers | 10.3203/IWF/C-1485eng (DOI) | |
| IWF Signature | C 1485 | |
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| Production Year | 1982 |
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| IWF Technical Data | Film, 16 mm, LT, 176 m ; F, 16 1/2 min |
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Transcript: English(auto-generated)
00:06
Plant damage by sedentary root nematodes. If the carrots in this field were closely examined,
00:23
it would be found that they were being attacked by sedentary root nematodes. The parasites have become established in the roots and are adversely affecting plant growth. By reducing quality, they cause considerable economic losses.
00:45
On the roots of the carrots, proliferations of tissue induced by the nematodes are obvious. These are called galls. The sedentary nematodes which produce such symptoms are root knot nematodes. The animals, in this case Melodogynae hapla, live within the galls.
01:05
Larger galls contain numerous animals. Other crops, such as potato, are parasitized by different sedentary root nematodes.
01:23
On the roots are numerous female nematodes, each about the size of the head of a pin. These sedentary nematodes belong to the group of cyst nematodes. The bright yellow spherical females belong to the species Globodera rostokiensis.
01:44
They are firmly attached to the root by their heads while their hind ends remain free. Within them, hundreds of eggs are formed. The roots of sugar beet can also be attacked by cyst nematodes.
02:04
These are the white, lemon-shaped females of Heterodera shaktiae. They are about one millimeter long. Living females are white, their bodies packed with eggs.
02:21
After death, the cuticle hardens and turns brown. Only then are they known as cysts. The brown cysts survive in the soil after harvest as sources of infection. When the next crop of sugar beet is planted, the infective larvae, which have already molted once, hatch from the eggs and leave the cyst.
02:49
Cyst nematodes and root knot nematodes have similar life cycles. The infective larvae are free-living and move through the soil in search of the roots of a host plant.
03:04
They attack the epidermal cells of the root with their robust mouth stylet to gain entry into the tissues.
03:26
This larva of Heterodera shaktiae has already penetrated through the epidermis. Its further progress is shown speeded up. The larvae prefer to attack the tissue of the root hair zone.
03:45
The root reacts to the invasion with distorted growth, as again shown speeded up. The site of invasion swells, the zone of elongation is shortened, and new root hairs grow close to the root tip.
04:07
In time, growth returns to normal. This root has been invaded by two larvae. At the invasion sites, the root hairs are extended,
04:22
an indication that growth of the root tip has twice been temporarily inhibited. As a result of the attack, two lateral roots develop.
04:56
Their growth is also distorted, just as that of the attacked root.
05:16
The infective larva has penetrated close to the root tip.
05:22
The growth of the root is now irreversibly halted. It turns brown. Close to the invading larva, on the left, a lateral root develops.
05:58
It grows undisturbed.
06:11
A more severe attack by cyst nematodes leads to the production of numerous lateral roots.
06:21
In the case of sugar beet, such a reaction prevents the production of the normal beet shape. One gets instead a beard of fine roots. Infestation with root knot nematodes leads to similar results. The main root of this carrot had already been damaged in an earlier stage.
06:40
As a substitute, lateral roots developed from which branched carrots of lower quality grow. The growth disruption of attacked roots and the consequent development of lateral roots constitute just one facet of the damage induced by sedentary root nematodes.
07:00
Damage due to nutrient deprivation begins as soon as the larvae have established themselves in the region of the vascular cylinder. The sedentary larva swells with constant nutrient uptake. Using Heterodera shatii as an example, the development of the larvae is shown speeded up.
07:27
This larva will molt twice more before reaching sexual maturity. This is the penultimate molting of a male larva, which in the laboratory takes about two days.
07:42
From this molt onwards, the larva is vermiform but will take no more food.
08:02
Within the larval cuticle, the male grows to a length of 1.5 mm. It will later leave this skin to mate with the female. The penultimate molt of a female larva.
08:36
Within approximately four days, the volume of the larva increases fivefold.
09:02
This is an adult pregnant female. It already has the lemon shape of the later cyst. Its head is anchored firmly in the tissue. Here the pumping organ, the esophageal bulb, with which the female continuously takes in food.
09:22
The nutrition of sedentary nematodes is always obtained from a highly developed nurse cell system, which is first induced and then maintained by the parasite. An extended nurse cell system can be seen in the center of the slightly swollen root.
09:50
In this severely attacked root, there are several nurse cell systems overlapping each other. Females and various larval stages have induced the development of numerous lateral roots.
10:23
This stained section shows the internal structure of the nurse cell system. As an example, that of Globodera rostokeensis. It is termed a syncytium, being composed of several cells between which the cell walls have been dissolved, leaving just a few remnants.
10:41
The syncytium has forced apart the vascular cylinder of the host and partly interrupted its xylem vessels, the green stained cell walls. The cell walls of the syncytium have become markedly thickened at their contact with the xylem vessels.
11:01
The thickened walls are sites of enhanced short-range solute transport. The nematode continuously extracts nourishment from the syncytium. The nutrients are increasingly drawn from the vessels into the syncytium. An electron microscope picture of this region shows that the cell wall has a labyrinthine structure
11:23
and has, as a result, a much increased surface area. The surface of the plasma lemma, which lines the cell wall ingroths, is also enormously enlarged.
11:44
This section shows a female root-knot nematode. It is enclosed by gall tissue. Around the head, nurse cells are formed, and from these the parasite gains its nourishment. They are enormously enlarged single cells and, just like syncytia, they markedly deform the vascular cylinder.
12:05
The mechanical and physiological damage to the root are the cause of growth disturbances and corresponding crop losses. Healthy carrot plants and those attacked by root-knot nematodes can grow alongside.
12:25
Symptoms of attack mean reduction in quality and can lead to especially high financial losses. Damage caused in the potato field by cyst nematodes is recognizable above ground by reduced growth.
12:50
The leaves of parasitized plants age prematurely and turn yellow.
13:01
At higher infestations of the soil, plants can be so much reduced that they are easily overgrown by weeds. Sugar beet also reacts to attack by cyst nematodes with obvious aerial symptoms.
13:25
The damage occurs in patches. The plants are stunted and, in warm weather, the leaves wilt.
13:49
A plant from the damaged patch is dug up. It was attacked at a much earlier stage.
14:06
A healthy beet from outside the patch serves as a comparison. The damaged beet has a beard of fine roots and lacks the typical beet shape. Because of the loss of nutrition and disrupted water transport, the typical shape could not develop.
14:25
Only healthy fields can produce a harvest, enabling the grower to remain competitive. By means of sound cultural practices, breeding for resistance and chemical control, the parasites can be suppressed sufficiently so that their damage threshold level is not exceeded.
14:45
But they are not easily eliminated.
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