1a.Objectives (from AD-416):
Determine whether reductions in corn growth and yield sometimes observed following a winter rye cover crop is caused by increased root pathogen infection originating in the glyphosate-treated cover crop.
1b.Approach (from AD-416):
Previous research showed that roots of glyphosate-treated plants have elevated populations of fungal pathogens (Fusarium, Pythium, and Rhizoctonia) which can infect subsequently planted crop plants. Reduced corn yields are sometimes observed following glyphosate-killed cover crops. This research would determine the levels of these pathogens in corn roots where corn is planted after rye cover crop killed with glyphosate or corn without a preceeding cover crop. This comparison would be carried out in field soil or field soil inoculated with these pathogens. The effect of fungicide seed treatments on disease will also be examined. Experiments would be conducted in growth chambers and in field plots.
Progress for this project focused on developing experimental procedures for both controlled environment and field studies, which have now been finalized. Controlled environment chambers were used in six experiments to examine the temperature and soil water conditions at which a cereal rye cover crop planted before corn can increase infection of corn seedlings. We determined that corn seedlings grown at 10ºC night temperatures and 12ºC day temperatures with the pot surface cover with perlite produced consistent corn plant growth and infection of seedlings in response to a preceding rye cover crop and corn seed fungal treatment. Eighty percent of the corn seedlings grown after rye had infected radicles compared with 30% of the corn seedling grown in pots that did not have rye preceding corn planting. Corn following rye also had shorter radicles and smaller shoots than control plants. Unexpectedly, seed fungicide treatments did not have a large affect on the level of infection following rye. Roots collected from these corn plants were surface sterilized and placed on selective media for Pythium and Fusarium to determine colonization by these seedling pathogens. In general, roots from corn plants grown in pots following rye had more fungal colonies than roots from corn plants that did not follow rye. Field plots with and without a rye cover crop were also established and both rye and corn plants were sampled to determine root infection and degree of fungal colonization. Results from these studies have not been analyzed and measurements of corn growth are continuing.