2013 Annual Report
Different procedures to determine microbial community structure have been used on these plots to determine relationships between diseases and microbe populations as influenced by tillage, cover crop, wheat grain crop and soybean planting timing. New research will involve more precise bacterial population determinations and whether they are gram negative or gram positive. Other research is indicating that this may have affects on nematode bacterial predation.
Biological control from bacterial predation is one aspect of management of soybean cyst nematode. Two new commercially available seed treatment nematicides contain gram positive bacteria as the active ingredient. One protects soybean roots and the other contains a parasite of soybean cyst nematode. Two bacterial parasites of soybean cyst nematode have been found in two research plots in Tennessee. One hyperparasite has been identified as Pasteuria nishizawae. The other is currently unidentified and was found in the tilled and no-tilled study area described above. In greenhouse studies, soil samples were collected from pots containing seed treated with a bacterial nematicide and from soil where the seed treatment was not present. The samples were processed for presence of gram positive bacteria using selective media (crystal violet agar). The number of colonies on crystal violet agar was compared to the number of colonies on the same media without crystal violet. Results showed that this technique could detect the presence of the bacterial nematicide in soil samples. This is the first step in detection of Pasteuria nishizawae in soil samples.
New work is also being planned on the effects of rotation crop and cover crop on charcoal rot levels. This will be conducted at the Milan Experiment Station in a long term study where soybeans are rotated with cotton and corn and both with grass and legume cover crops established in each rotation each year. Presently the plots are in their second three year cycle of rotations.