Submitted to: Journal of Nematology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: September 15, 1998
Publication Date: N/A
Interpretive Summary: Because plant-parasitic nematodes (microscopic worms that attack plants) cause seven billion dollars of agricultural losses annually in the United States, an important problem to be solved is how to reduce these crop losses. The fungus Verticillium lecanii, which can cut back nematode numbers in soil, was studied to determine how it attacks nematodes. The fungus was placed on soybean cyst nematode, and the interaction between th two organisms was observed by means of light microscopy and scanning electron microscopy. The nematode stages studied were those that produce eggs (females) and dead females that serve as protective structures for eggs (cysts). Female and cyst colonization followed similar patterns. Sixteen hours after the fungus was placed on the nematode, the fungus grew on groups of eggs located outside the female and cyst bodies. Within a week, the fungus was growing throughout egg masses, but was not seen parasitizing live eggs. Fungus penetration holes in female and cyst walls were observed three days after the fungus was placed on the nematode. Colonization inside female and cyst bodies ranged from none to extensive. This research demonstrates the way in which the nematode is attacked by the fungus. The results will be used by scientists developing environmentally safe methods for managing nematodes that attack plants.
Technical Abstract: The fungus Verticillium lecanii was studied as a potential management agent for the plant-parasitic nematode Heterodera glycines. Monoxenic cultures of H. glycines on soybean roots were inoculated with V. lecanii. This allowed for evaluation of physical and structural interactions between the two organisms while the nematode was attached to roots, and prevented contamination with other fungi. Some females and cysts were removed from monoxenic cultures and placed on water agar prior to inoculation. This was comparable to procedures used in other studies of fungi that colonize nematodes. One, two, three, four, seven, and fourteen days after inoculation, females and cysts with attached egg masses were examined with the light microscope, or chemically fixed for conventional scanning electron microscopy (SEM). At 16 hours and again at eight days after inoculation, frozen hydrated specimens were observed with low-temperature SEM. Female and cyst colonization followed similar patterns. Sixteen hours after fungus inoculation, hyphae grew on and just inside external egg masses. Within a week, hyphae proliferated throughout the gelatinous matrices of some egg masses, but were not observed parasitizing live eggs. Fungus penetration holes in female and cyst walls were observed three days after inoculation; internal colonization ranged from none to extensive mycelial growth.