Discovery and Development of Bioherbicides
Weed
technology and weed management strategies are continually changing
to meet emerging challenges in agriculture. A number of weeds consistently
escape, or are unsuited to current weed management technologies,
and pressure continues to increase upon the use of certain herbicides
due to concerns of adverse environmental and human health impacts.
It is important that a diverse array of effective, sustainable, and
environmentally benign weed control tools and methodologies remain
available to producers.
Weeds, like all plants, are host to a wide range of pathogens.
Under natural conditions, these plant pathogens rarely have
a dramatic impact,
due to limitations of the environment, the host, or the pathogen.
Many plant pathogens, however, have the potential to cause
dramatic epidemics
under optimal or manipulated conditions. The principle of the bioherbicide
approach is to release a weed pathogen from the natural regulation
that limits its effect, and to develop an artificial epidemic which
is sufficiently rapid, damaging and sustained to deliver a desired
level of control within a particular production system. The disease
epidemic should not cause damage to non-target plants or other organisms,
and should decline through time towards its original size under the
normal constraints of the environment. Our goal is to develop plant
pathogens as products which can be fully integrated into production
systems to deliver economic and environmentally safe weed management.
Bioherbicides have particularly strong potential to be developed
as weed control products for niche markets for which chemical
herbicides
are unavailable or poorly suited. The cost of developing a bioherbicide
is intrinsically much lower than that of a chemical herbicide, and
bioherbicides can deliver economic weed control with minimal environmental
impact.
Interactions
Between Chemical Herbicides and the Candidate Bioherbicide Microsphaeropsis amaranthi on Waterhemp
Waterhemp (Amaranthus
tuberculatus) has become a dominant weed
of Midwestern corn/soybean in the last decade. The ascendance
of waterhemp
has been
due, in part, to the development of a wide range of biotypes
resistant to various herbicides. Of particular concern is the
possibility
that waterhemp biotypes have developed resistance to glyphosate.
David
Smith
|
David
Smith is conducting his MS in this laboratory investigating the
response to glyphosate of a range of different populations of
waterhemp from Ohio, Indiana, Missouri, Illinois and Iowa. He
has shown that there is a range of different responses (Figure
1).
Additionally, David is studying the interactions between
a candidate bioherbicide fungus, Microspaeropsis amaranthi,
and chemical herbicides.
He has shown that sub-lethal rates of glyphosate can predispose
waterhemp to infection by M. amaranthi (Figure 2). |
Figure 1. Clone ALT1 from Altamont, IL shows significant levels of
resistance. Plants treated with glyphosate concentrations significantly
higher than the recommended rate (1X = 0.63 kg ae/ha) were not killed.
Plants treated with the recommended rate were only slightly stunted.
Figure
2. Dry weight of A. tuberculatus treated with glyphosate and Microsphaeropsis
amaranthi in a split-application. Bars with the same letter(s) are
not significantly different (P=0.05).
Soil
Microbial Ecology
Kathy
Anderson is using the molecular technique Denaturing Gradient Gel
Electrophoresis of PCR-amplified ribosomal RNA genes (PCR-DGGE) to
investigate the microbial ecology of weed roots, and the soil that
surrounds them.
Kathy
Anderson
|
PCR-DGGE can be used to analyze the composition
of microbial communities from DNA extracted directly from the
soil. Consequently, the technique can be used to study the large
number of species that can not be readily grown in culture.
This
technique is being used to study the changes in soil microbial
communities that occur under different management
systems, including
different types of tillage, nutrient management and weed management. |
Future research will apply this technology to the analysis of the
effect of organic vegetable production upon the microbial ecology of
soils. Additionally, we anticipate developing research that will apply
PCR-DGGE to the analysis of the microbial ecology of crops in developing
countries that are infested by the root parasitic weeds Striga (witchweeds)
and Orobanche (broomrapes).
|
This gel represents a preliminary investigation
of the microbial ecology of red clover (Trifolium pratense) during
parasitism by clover broomrape (Orobanche minor), and demonstrates
that different organisms inhabit the rhizosphere of the parasite
(O. minor) and the host (T. pratense), even though the two root
systems were excavated from the same hole. Each band represents
a different species of microbe from the soil sample.
Lane M: Marker sequences, Lanes 1-4. Profiles for O.
minor rhizosphere soil. Lanes 5-8: Profiles for T.
pratense rhizosphere soil. Bands
1-3: Unique to O. minor. Band 4: Unique to T. pratense. |
Future
Projects
A number
of research projects are under development, including:
Beed, FD, SG Hallett, J Venne & AK Watson. 2007. Biocontrol using Fusarium oxysporum: a critical component of integrated Striga management. In: J Gressel & G Ejeta (eds) Integrating New Technologies for Striga Control: Towards Ending the Witch-Hunt. World Scientific Publ. Co. Inc., Hackensack, NJ.
Callaway, RM, D Cipollini, K Barto, GC Thelen, SG Hallett, D Prati, K Stinson & JN Klironomos. 2007. An invasive plant suppresses fungal mutualisms in America but not in its native Europe. Ecology. In Press.
Davis, AS, KI Anderson, SG Hallett and KA Renner. 2006. Weed seed mortality in soils with contrasting agricultural management histories. Weed Sci. 54:291-297.
Hallett, SG. 2006. Dislocation from coevolved relationships: a unifying theory for plant invasion and naturalization? Weed Sci. 54:282-290.
Smith, DA, DA Doll, D Singh & SG Hallett. 2006. Climatic constraints to the potential of Microsphaeropsis amaranthi as a bioherbicide for common waterhemp. Phytopathology 96:308-312.
Smith, DA & SG Hallett. 2006. Interactions between chemical herbicides and the candidate bioherbicide Microsphaeropsis amaranthi. Weed Sci. 54:532-537.
Smith, DA & SG Hallett. 2006. Variable response of common waterhemp (Amaranthus rudis Sauer) to glyphosate. Weed Technol. 20:466-471.
Stinson, KA, S Campbell, JR Powell, BE Wolfe, RM Callaway, GC Thelen, SG Hallett, D Prati & JN Klironomos. 2006. Invasive plant suppresses the establishment and growth of native trees by allelochemical disruption of belowground mutualists. PLoS Biology 4:727-731.
Doll, DA, PE Sojka & SG Hallett. 2005. Factors affecting the efficacy of spray applications of the bioherbicidal fungus Microsphaeropsis amaranthi. Weed Technol. 19:110-115.
Héraux, FMD, SG Hallett & SC Weller. 2005. Combining Trichoderma virens-inoculated compost and a Rye Cover Crop for Weed Control in Transplanted Vegetables. Biological Control 34:21-26.
Héraux, FMD, SG Hallett & SC Weller. 2005. Composted Chicken Manure as a Medium for the Production and Delivery of Trichoderma virens for Weed Control. Hortscience 40:1394-1397.
Hallett, SG. 2005. Where are the Bioherbicides? Weed Sci. 53:404-415.
Anderson, KI & SG Hallett. 2004. Herbicidal spectrum and activity of Myrothecium verrucaria. Weed Sci. 52:623-627.
Léger, C, SG Hallett & AK Watson. 2001. Performance of Colletotrichum dematium for the control of fireweed (Epilobium angustifolium) improved with formulation. Weed Technol. 15:437-446.
Brière, SC, AK Watson, TC Paulitz & SG Hallett. 2000. Oxalic acid production and mycelial biomass yield of Sclerotinia minor for the formulation enhancement of a granular turf bioherbicide. Biocontrol Sci. Technol. 10: 281-289.
Masangkay, RF, TC Paulitz, SG Hallett & AK Watson. 2000. Characterization of sporulation of Alternaria alternata f. sp. sphenocleae. Biocontrol Sci. Technol. 10:385-397.
Masangkay, RF, TC Paulitz, SG Hallett & AK Watson. 2000. Solid substrate production of Alternaria alternata f. sp. sphenocleae Conidia. Biocontrol Sci. Technol. 10:399-409.
Masangkay, RF, TC Paulitz, SG Hallett & AK Watson. 1999. Factors influencing biological control of Sphenoclea zeylanica with Alternaria alternata f.sp. spenocleae. Plant Dis. 83:1019-1024.
Yu, X, SG Hallett, J Sheppard & AK Watson. 1998. Effects of carbon concentration and carbon to nitrogen ratio on growth and sporulation of Colletotrichum coccodes in a cyclone column bioreactor. J. Ind. Microbiol. Biotechnol. 20: 333-338.
Yu, X, SG Hallett, J Sheppard & AK Watson. 1997. Application of the Plackett-Burman experimental design to evaluate nutritional requirements for the production of Colletotrichum coccodes spores. Applied Microbiol. Biotechnol. 47:301-305.
Ciotola, M, AK Watson & SG Hallett. 1996. Discovery of an isolate of Fusarium oxysporum with potential to control Striga hermonthica in Africa. Weed Res. 35:303-309.
Diarra. C, M Ciotola, SG Hallett, DE Hess & AK Watson. 1996. Field efficacy of Fusarium oxysporum for the control of Striga hermonthica. Nuisibles Pests Pragas 4:257-263.
DiTommaso, A, AK Watson & SG Hallett. 1996. Infection by the fungal pathogen Colletotrichum coccodes affects velvetleaf (Abutilon theophrasti)-soybean competition in the field. Weed Sci. 44:924-933.
Brière, SC, AK Watson, TC Paulitz & SG Hallett. 1995. First report of a Phoma sp. on common ragweed in North America. Plant Dis. 79:968.
Paul, ND, PG Ayres, & SG Hallett. 1993. Mycoherbicides and other biological control agents for Senecio spp. Pesticide Sci. 37:323-329.
Hallett, SG & PG Ayres. 1992. Invasion of rust (Puccinia lagenophorae) aecia on groundsel (Senecio vulgaris) by secondary parasites: death of host. Mycol. Res. 96: 142-144.
Paul, ND, PG Ayres & SG Hallett. 1992. Making biological herbicides more effective. J. Biol. Educ. 26: 94-99.
Hallett, SG, P Hutchinson, ND Paul & PG Ayres. 1990. Conidial germination of Botrytis cinerea in relation to aeciospores and aecia of groundsel rust (Puccinia lagenophorae). Mycol. Res. 94:603-606.
Hallett, SG, ND Paul & PG Ayres. 1990. Botrytis cinerea kills groundsel (Senecio vulgaris) infected by rust (Puccinia lagenophorae). New Phytol. 114:105-109.