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 from March 1 - July 1, 2012, is preliminary as experimental procedures and protocols were being developed. Controlled environment chambers were used in two 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. These experiments were successful in that increased infection was documented in corn seedlings following a rye cover crop, but additional work is required to develop a root disease rating index and standardized measurement protocol. These experiments will be repeated at different temperatures to find the optimum temperature and sampling time for differentiating treatments and to further develop the measurement protocols. Additionally, these initial experiments allowed us to test laboratory procedures for isolating Fusarium and Pythium isolates using selective media from both cereal rye and corn root tissues. After isolates were obtained from rye roots they were used to infect corn seedlings to test their pathogenicity. Fusarium and Pythium isolates were also obtained from both cereal rye and corn plants taken from the field. These preliminary results are the initial steps in addressing the objective of this project to 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.