Submitted to: Journal of Nematology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: November 28, 1999
Publication Date: N/A
Interpretive Summary: Plant-parasitic nematodes are microscopic worms that attack plants, causing seven billion dollars in crop losses annually in the United States. The problem being addressed is finding new ways of reducing crop losses caused by nematodes. The fungus Verticillium lecanii is being studied as a potential management agent for a nematode that attacks soybean plants. One echaracteristic that helps fungi act against plant-parasitic nematodes is the ability to grow on the surface of plant roots, where many nematodes attack plants. This fungus was placed near roots growing on a culture medium. When the fungus was applied to roots that were two weeks old, it grew on the surfaces of many roots. Length of root contacted by the fungus was 35% - 51% of total root length. The fungus was less likely to grow on surfaces of younger roots, especially when other food sources were present. However, when soybean cyst nematode was on the roots, the fungus eventually ygrew on the root surfaces. Root contact length was 49% - 51% of total root length. When soybeans were grown in soil, the fungus was not found in association with many roots. Other organisms in the soil may have been better competitors in that location. Use of this fungus for nematode management would depend upon improving the ability of the fungus to compete on root surfaces. This research will be used by scientists developing environmentally safe methods for reducing crop losses caused by nematodes.
The potential biocontrol fungus Verticillium lecanii was inoculated onto soybean roots in root tip explant cultures. Verticillium lecanii grew in association with more than half of the older soybean roots (cultures two weeks old at the time of fungus inoculation). Root contact length was 4.5- 6.0 cm, equivalent to 35%-51% of total root length. On younger roots (cultures four days old at the time of fungus inoculation), V. lecanii was less likely to colonize root surface areas when applied on a potato dextrose disc than when applied as an aqueous suspension. However, when soybean cyst nematode was present on the roots, root colonization did occur four weeks after inoculation. Root contact length was 3.9-4.3 cm, equivalent to 49%-51% of total root length. Scanning electron microscopy revealed that the fungus grew in close association with root surfaces, and even colonized root cortical cells. When soybeans in sandy soil and in loamy sand were treated with V. lecanii in alginate prills, the fungus was found at greater depths in the sandy soil than in the loamy sand, and tended to be associated with root washes rather than soil outside the rhizosphere. However, few isolations were made from either the rhizosphere or soil of either soil type.