2011 Annual Report
1a.Objectives (from AD-416)
Discover, develop, and improve augmentative bioherbicides, as viable weed biocontrol products through innovative field application, formulation, and mass-production strategies. Develop methodologies to eliminate, reduce or regulate undesirable secondary metabolites from biocontrol pathogens. Discover disease-promoting or weed defense-inhibiting chemicals that synergize bioherbicide. Identify or create biocontrol pathogens with novel traits. Develop molecular markers for bioherbicide strain identification, post-release monitoring, and environmental risk assessment. Discover novel information on genetic determinants and regulation mechanisms of pathogenicity, e.g., virulence, stability, host range and phytotoxin production.
1b.Approach (from AD-416)
Assess biocontrol potential of several pathogens for control of various weeds: Myrothecium verrucaria for kudzu, redvine, and trumpetcreeper, Colletotrichum truncatum for hemp sesbania, and C. gloeosprioides cassiae for sicklepod. Assess formulations, interactions with agrochemicals, and application timing under field conditions. Assess combinations of host-specific bioherbicides to broaden the weed control spectrum. Develop methodologies for mass production and formulation to improve stability and virulence of bioherbicides. Reduce or eliminate undesirable secondary metabolites (e.g. trichothecenes) from M. verrucaria through mutagenesis, fermentation modifications, growth media alterations, strain selection, use of metabolic regulators, purification, and filtration of pathogen cultures. Inhibitors and other methods to metabolically inactivate trichothecene synthesis in M. verrucaria will be examined. Monitor toxin production via HPLC, ELISA, and HPLC-MS. Assay plant tissues from laboratory, greenhouse and field tests to determine enzyme and secondary plant constituent levels related to weed defense mechanisms against pathogens. Implement biochemical analyses of biomarker defense enzymes and plant constituents to ascertain mechanism of action of the pathogen and the synergistic action of combination of herbicides and other compounds with pathogens. Develop molecular methods for strain identification and post-release monitoring during field testing. Assess the ecological competence of biocontrol agents and the influence of environmental and weed host factors in field and controlled model systems.
This is the final report for the project. Substantial results were realized over the 5 years of the project. For example, fermentation methods were developed that resulted in greatly reduced toxins in the fungus Myrothecium verrucaria for controlling the invasive weed kudzu. It was discovered that toxin production in this fungus could be altered by cultural conditions, and that when grown in liquid culture, the fungus was nearly void of toxins. Carbon and nitrogen types and quantities were also found to alter toxin accumulation. It was demonstrated that tests for toxins could be done by using relatively inexpensive assay kits. The mixtures of this fungus and others could be mixed with certain glyphosate herbicides formulations, resulting in greatly improved weed control of redvine, trumpetcreeper, and Hemp sesbania. It was demonstrated that commonly available non-ionic (and one organic) surfactants also promote infection by this fungus, and that the growth hormone herbicide quinclorac exhibited unique interactions using in vitro bioassays with several weed hosts. Weed control was greater when mixtures of plant pathogenic fungi were applied in narrow row spaced soybean test plots as compared to weed control obtained in wider row spacings, and that some vegetable oils, such as corn oil, greatly improves weed control. Formulation research with Hemp sesbania and the northern jointvetch pathogen Colletotrichum gloeosporioides f. sp. aeschynomene showed that Hemp sesbania was not infected by fungal spores alone, but was highly susceptible to infection when formulated in an invert emulsion. The research over the term of this project was designed to improve the weed control efficiency of several different biological weed control plant pathogens, which may eventually result in commercial products. The major impacts, such as formulation technologies developed during this research, have resulted in adaptation of these techniques at several other research facilities in the U.S. as well as in several other countries. ARS researchers at Stoneville, MS, published some of the only results worldwide, demonstrating that when successful bioherbicidal weed control was achieved, increased crop yields resulted.