Submitted to: Journal of Nematology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 10, 2001
Publication Date: N/A
Interpretive Summary: Plant-parasitic nematodes are microscopic soil worms that cause nine billion dollars of U.S. agricultural losses each year. Because the chemicals used for controlling nematodes are not very safe to humans or the environment, scientists are developing new methods of control using natural enemies of nematodes, such as bacteria and fungi. One problem with using these naturally occurring organisms as biological control agents is that many of them would be expected to attack nematode eggs but do not. In this report, scientists at Beltsville in collaboration with a visiting scientist from Israel describe experiments to determine if the material surrounding nematode eggs protects them from attack by bacteria and fungi. This material is produced by the female nematode and is called the "gelatinous matrix". The scientists discovered that eggs stripped of the gelatinous matrix have much less potential to damage tomato plants than eggs surrounded by the gelatinous matrix. Examination with a microscope revealed that some bacteria and fungi are retarded by presence of the gelatinous matrix. The results are significant because they provide the first quantitative measurement of the protection the gelatinous matrix provides to nematode eggs. This research will be used by scientists developing biologically based methods for nematode control; the research will eventually benefit the public by providing safe methods of protecting crops against nematode-induced damage.
The survival of eggs of the root-knot nematode Meloidogyne javanica was studied in a series of experiments comparing the infectivity of egg masses (EM) to that of separated eggs (SE). The EM or SE were placed in the centers of pots containing citrus orchard soil incubated for 24 hours and 10 and 20 days. Following each incubation time, two-week-old tomato plants were planted in each pot, and three weeks later the plants were harvested and the galling index was determined. In the EM treatments a galling index of 4.5 was recorded, while in the SE treatments the infectivity rate gradually declined to trace amounts in proportion to the duration the EM had been incubated in the soil. Exposing EM and SE to soil disinfested with formaldehyde resulted in comparable galling indices. In petri dish experiments, 100 mg of natural soil was spread at the perimeter of a Phytagel surface and EM or SE were placed in the center. Light microscopy revealed that within 5-10 days the SE were attacked by a broad spectrum of microorganisms and were obliterated while the eggs within the EM remained intact. Separated eggs placed within sections of gelatinous matrix were not attacked by the soil microorganisms. As the major difference between the EM and the SE was the presence of the gelatinous matrix, the gelatinous matrix may serve as a barrier to the invasion of some microorganisms.