2007 Annual Report
Isolation and purification of antimicrobial molecules in kochia and jimsonweed seed exudates began in Summer 2007 and will continue through Spring 2008. Results from these experiments will be used to formulate and test hypotheses regarding the potential utility of these compounds to target specific plant pathogens.
Weed seed destruction by seed predators may play an important role in keeping weed populations manageable. Long-term seed predation studies were initiated in Fall 2004 to determine the impact of crop habitat on seed predation rates of giant ragweed, velvetleaf and giant foxtail by small vertebrates and insects. Point estimates and quarterly measurements of seed predation rates began in Fall 2005 and will continue through Fall 2008. Results will help guide the design of cropping systems with increased rates of weed seed loss due to predation.
No-till soybean production requires intensive herbicide use to replace the weed suppressive benefits of tillage and field cultivation. A new tool for managing cover crop residues in no-till soybean systems, a cover crop roller-crimper, was compared in 2005 and 2006 to the traditional burndown herbicide treatment for cover crop residue management. Weed growth, soil properties and crop yield loss were measured to understand how the different systems function. Measurements will be repeated in 2007. These results will benefit all field crop producers, but will be of special benefit to organic producers, for whom no-till production is currently unfeasible.
2. Sweet corn competitive ability as a tool in weed management. Weed management systems in sweet corn are characterized by extensive use of soil-applied herbicides, many facing increased regulatory scrutiny, and recent surveys indicate that over one-half of commercial sweet corn fields suffered yield losses due to weed interference. Although sweet corn hybrids vary extensively in plant architecture, the implications of sweet corn canopy variation on crop/weed interactions were until recently unstudied. As a result of research from ARS locations in Illinois and Washington, commercially-available sweet corn hybrids were found to vary considerably in competitive ability with weeds, and several crop traits responsible for this variation were identified. Sweet corn traits conferring competitive canopy architecture make consistent contributions to weed management. The potential impact from this research is that growing commercially-available hybrids with canopies that are competitive with weeds, or breeding for hybrids with more competitive canopy architecture, offer tangible improvements to weed management systems. This accomplishment addresses National Program 304, Crop Protection & Quarantine, Component X – Weed Management Systems, Problem Statement Xb - Integrated Weed Management in Cropland.
3. Seed-borne antimicrobial compounds from invasive weed species. One notable characteristic of invasive weed species is their ability to form soil seed banks that are seemingly more resistant to infection than their cultivated counterparts. This trait may partially account for the persistence of weed species in agricultural plots. To determine the mechanism by which weed seeds fend off infection, water-soluble exudates from 10 plant species were tested for antagonistic activity against 15 fungi and 7 bacteria. Of the plants tested, exudates from two weed species demonstrated antimicrobial activity against Clavibacter michiganense ssp. nebraskense, an important bacterial phytopathogen that infects tomato plants or inhibited the fungi Colletotrichum graminicola and Taphrina deformans (the causative agents of maize anthracnose and fruit tree leaf curl, respectively). It has long been assumed that phenolic acids, which disrupt microbial cell membranes, constitute the seed’s primary defense against infection. However, even seeds that lacked demonstrable antimicrobial activity had significant phenol concentrations, and there was a clear lack of correlation between phenol content and antimicrobial activity. Further physical and chemical characterization of seed exudates revealed that the antimicrobial compound(s) are likely proteinacious in nature. This work suggests that weed seeds utilize a specific suite of antimicrobial proteins to fend off microbial infection and degradation, and this may play an important role in weed persistence. The results have led to investigation of possible interest in the private sector and future cooperative research relationships. This accomplishment addresses National Program 304, Crop Protection & Quarantine, Component VII - Weed Biology and Ecology, Problem Statement VIId - Reproductive Biology and Seed Bank Dynamics.
Davis, A.S., Landis, D.A., Nuzzo, V., Blossey, B., Gerber, E., Hinz, H. 2006. Demographic models inform selection of biocontrol agents for garlic mustard. Ecological Applications. 16:2399-2410.
Pataky, Jerald K., Norby, John N., Williams, M., Riechers, D.E. 2006. Inheritance of cross-sensitivity in sweet corn to herbicides applied postemergence. Journal of the American Society for Horticultural Science. 131:744-751.
Williams, M. 2006. Planting date influences critical period of weed control in sweet corn. Weed Science. 54:928-933.
Lundgren, J.G., Lehman, R.M., Chee Sanford, J. 2007. Bacterial communities within the digestive tracts of ground beetles (Coleoptera: Carabidae). Annals of the Entomological Society of America. 100:275-282.
Williams, M., Boydston, R.A., Davis, A.S. 2007. Wild proso millet (Panicum miliaceum) suppressive ability among three sweet corn hybrids. Weed Science. 55:245-251.
Williams, M., Boydston, R.A., Davis, A.S. 2006. Canopy variation among three sweet corn hybrids and implications for light competition. HortScience. 41:1449-1454.
Koike, S., Krapac, I.G., Oliver, H.D., Yannarell, A.C., Chee Sanford, J.C., Aminov, R.I., Mackie, R.I. 2007. Monitoring and source tracking of tetracycline resistance genes in lagoons and groundwater adjacent to swine production facilities over a three-year period. Applied and Environmental Microbiology. 73(15):4813-4823.
Raghu, S., Anderson, R.C., Daehler, C., Davis, A.S., Wiedenmann, R.N., Simberloff, D., Mack, R.N. 2006. Adding biofuels to the invasive species fire? Science. 313:1742.
Williams, M., Masiunas, J.B. 2006. Functional relationships between giant ragweed (Ambrosia trifida L.) interference and sweet corn yield and ear traits. Weed Science. 54:948-953.
Ortiz Ribbing, L.M., Williams, M. 2006. Conidial germination and germ tube elongation of Phomopsis amaranthicola and Microsphaeropsis amaranthi on leaf surfaces of seven Amaranthus species. Biological Control. 38(3):356-362.