Time-lapse video of a root-knot nematode (M. incognita) entering a melon root tip.
Mi root tip (1.2 mb file size).
|Close-up video of M. incognita egg masses on tomato roots. The egg masses were stained dark blue to make them easier to see with the naked eye. There is usually between 200 to 400 eggs in each egg mass.
Mi egg masses (3.8 mb file size).
|Close-up video of Paratrichodorus feeding on a sudan grass root.
Paratrichodorus feeding (1 mb file size).
Time-lapse melon video.
This video shows the symptoms of root-knot nematode (M. incognita) infestation on melon. The symptoms are typical for what we have seen in many different experiments. Initially there does not appear to be a strong effect of the nematodes, as seedlings will emerge even under high nematode pressure. However, soon after emergence, these seedlings will stop growing, become yellow, wilt and die. Under moderate nematode pressure seedlings survive, but over time, there is an obvious reduction in growth.
Melon cv. Durango were sown in pots filled with steam-sterilized sand and inoculated at the same time. Pots were placed at 26 C and filmed daily for a few seconds.
Melon (1.7mb file size)
|This video shows the common relationship between pre-plant nematode densities and plant growth (the damage function) as developed by Seinhorst (e.g. Fundamental and Applied Nematology, 21: 459-468).
The general formula is shown. Two axes are drawn, with the relative yield on the y-axis. The "Yield" is in blue and the corresponding Y' in the formula also changes to blue. The initial nematode population is drawn on a logarithmic scale in blue, and the corresponding Pi in the formula changes to blue. A line appears representing the 100% yield. The line curves down at the Pi level of 10 nematodes, and the letter T, representing the tolerance limit, appears. T in the formula changes to blue. The curve continues until it levels of, and the M representing the minimum yield appears, and changes to blue in the formula. Finally, a red curve appears, to show the shape of a curve with higher T and m values (e.g. curve for a more tolerant crop or cultivar).
Graph (988kb file size)
|Root-knot nematodes, surviving as eggs in the soil during the winter, start to hatch from the eggs in spring as the soil temperature increases (hatched J2=red, eggs=red ovals, empty egg-shells=black C-shaped). As a host crop is sown and seedlings germinate, the juveniles start to migrate towards the roots. The juveniles enter the roots close to the root tip. A juvenile (stained pink) just after it has penetrated the root, can be seen in the first pop-up photograph. The nematodes become immobile and start to swell. The root responds with swelling. Juveniles molt, keep swelling and galling is now easily visible on the roots. Adult females, which are melon-shaped (= Meloidogyne), deposit egg masses in a gelatinous matrix on the outside of the roots. Eggs develop, new J2's hatch from the eggs and the cycle is repeated.
Rk Life cycle (6.3mb file size)
|Lesion nematodes surviving in the absence of a host as eggs or free-living stages, start moving towards the roots of a newly germinated host crop. Over time more and more nematodes aggregate around the roots and start penetrating the roots. Unlike root-knot nematodes, lesion nematodes do not necessarily enter the roots in the root-tip zone. The nematodes keep migrating even after they have entered the roots, causing extensive damage to the root tissue. This tissue may die completely which results in necrotic root lesions. The damaged roots often become infected with secondary pathogens (e.g. bacteria or fungi) adding to the problem. Lesion nematodes can move into and out of the roots throughout their life. The females deposit single eggs, inside the roots or into the soil, from which second stage juveniles hatch.
The "cartoon" like part of the life cycle, is followed by low-power magnification images of nematodes moving through agar and "locking on" roots (corn). The following high power magnification part shows a nematode penetrating into the root (top right hand side), while other nematodes can be seen feeding and moving inside the roots. This is followed by a slow motion part of female laying an egg, and finally a new juvenile hatching from the egg.
Lesion Life Cycle (8.1mb file size)
|Gravid Longidorus africanus females were collected washed with sterile water, and transferred to water agar. Females were removed from the agar after eggs had been deposited. Eggs were filmed using time lapse video. Unfortunately the latter part showing the hatching of the juvenile from the egg did not translate well from video-tape into digital format. We'll try to get better pictures at some point.
Egg (2.5 mb file size)
|Second-stage Meloidogyne incognita were inoculated into the left side of a growth pouch with melon (var. Durango). The right side was not inoculated. The roots were filmed over a two week period. A few days after inoculation, galls are forming on the inoculated roots. Galling is clearly visible two weeks after inoculation.
Galling (6.5mb file size)