ANNUAL REPORT OF COOPERATIVE REGIONAL RESEARCH PROJECTS
Supported by Allotments of the Regional Research Fund
Hatch Act, as amended August 11, 1955
S-268
Evaluation and Development of Plant Pathogens for Biological
Control of Weeds
Report for October 1, 1997 to September 30, 1998
Regional Research Project, S-268
Evaluation and Development of Plant Pathogens for Biological Control of Weeds
Approved for 5 years, October 1, 1995 to September 30, 2000
Annual Report for October 1, 1997 to September 30, 1998
Submitted May, 1999
Organization, Cooperating Agencies, and Principal Leaders Organization:
David H. Teem, Administrative Advisor SAES, AL
Robin N. Huettel, CSREES Representative USDA, CSREES
R. Charudattan, Project Chairman SAES, FL
Donald J. Daigle, Secretary USDA-ARS, LA
Thomas A. Bewick, Annual Meeting Chairman SAES, MA
C. Doug. Boyette, Chairman, Objective 1 USDA-ARS, MS
David O. TeBeest, Chairman, Objective 2 SAES, AR
William M. Connick, Chairman, Objective 3 USDA-ARS, LA
Norman W. Schaad, Chairman, Objective 4 USDA-ARS, MD
Cooperating States and Members:
Alabama
Fenny K. Dane SAES
J.A. Shaw SAES
Arkansas
David O. TeBeest* SAES
Gregory J. Weidemann SAES
Florida
R. Charudattan* SAES
Erin N. Rosskopf* USDA-ARS
Illinois
Mark A. Jackson* USDA-ARS
Iowa
Abraham H. Epstein* SAES
Louisiana
William M. Connick* USDA-ARS
Donald J. Daigle USDA-ARS
Rex W. Millhollon USDA-ARS
Maryland
Efstathios Hatziloukas USDA-ARS
Douglas G. Luster USDA-ARS
C. Mischke USDA-ARS
Norman W. Schaad USDA-ARS
Shaw-Ming Yang USDA-ARS
Massachusetts
Frank L. Caruso* SAES
Thomas A. Bewick SAES
Minnesota
Robert F. Nyvall SAES
Mississippi
Hamed K. Abbas USDA-ARS
C. Douglas Boyette* USDA-ARS
Robert E. Hoagland USDA-ARS
North Carolina
Joe C. Neal* SAES
Wisconsin
Herb J. Hopen* SAES
*Principal Leaders/Voting Members
Participants in the 1999 Meeting:
Bailey, Karen Agric. & Agri-Food, Sask., Canada
Bewick, Tom SAES, MA
Boyetchko, Susan M. Agric. & Agri-Food, Sask., Canada
Boyette, Doug USDA-ARS, SWSRU, MS
Brooker, Nancy L. Pittsburg State Univ., KS
Bruckart, William L. USDA-ARS, MD
Caruso, Frank L. SAES, MA
Charudattan*,R. SAES, FL
Connick, William M. USDA-ARS, LA
Daigle, Donald J. USDA-ARS, LA
den Breeyen, Alana ARC-PPRI, South Africa
Escandari, Farivar USDA-ARS
Johnson, David R. SAES, MN
Marshall, Lucia G.I. TAPT, MO
Mika, Jane SAES, MA
Ostrowski, Richard United Agric Products, CO
Porter, John C. SAES, MA
Rosskopf, Erin N. USDA-ARS, FL
Teem, David H. Auburn University, AL
Zhang, Wenming Alberta Research Council, Canada
PROGRESS OF WORK AND PRINCIPAL ACCOMPLISHMENTS
Progress Reports on Cooperative Projects: COLTRU, Dodder, and PST
Prospects for the commercial use of the fungus Colletotrichum truncatum
(COLTRU) as a bioherbicide for hemp sesbania (Sesbania exaltata) in
cotton, rice, and soybean were assessed under the leadership of D. Boyette
(MS). Under narrow-row planting with less cultivation, sicklepod (Senna
obtusifolia) and coffee senna (Cassia obtusifolia) could not compete with
crops if the weeds were treated with COLTRU at preplanting. Hemp sesbania
was 100% controlled in soybean fields treated with invert emulsions or
unrefined corn oil emulsions containing COLTRU.
Evaluation of Alternaria destruens to control dodder in cranberry,
safflower, tomato, and carrot was continued under the leadership of T.
Bewick (MA). United Agri Products (CO) partnered with Sylvan (PA) to
produce inoculum for field tests. Results of preemergence treatments with
Pesta granules in safflower and carrot (WI) and in cranberry (MA) fields
were inconclusive since dodder could not be found in both the control and
treated fields (states involved: LA, MA, and WI). Preemergence
treatments of cranberry fields with the fungus (WI) also did not affect
the area of plot coverage by dodder. Postemergence spray treatment
controlled dodder at 90% or better at an inoculum rate of 1010 conidia per
acre. In tomatoes (CA), 85% control of dodder was achieved with a
combination of pre- and postemergence treatments. About 10 g (1010
conidia) in 30 gal of suspension was enough to treat one acre. Plans for
the coming year include trials in CA and OR. It is hoped that the fungus
will be registered for the 2000 growing season. EPA is expected to
expedite the review for registration.
Efforts to develop Pseudomonas syringae pv. tagetis (PST) continued with
the following cooperators: H. Abbas (MS), T. Bewick (MA), S. Boyetchko
(Canada), J. Gronwald (MN), R. Kremer (MO), J. Neal (NC), T. Wheeler (TX),
and N. Zidack (MT). Higher rates of Silwet L-77 (0.5 to 1.0%) in lower
total volumes (10 to 20 gallons/acre) increased PST efficacy, and a cell
density of 108 cells/ml was effective for the control of Canada thistle.
A flash-frozen PST product is under development. Cocklebur could be
controlled with PST in trials conducted in Mississippi (H. Abbas and D.
Johnson, MN). Three organosilicones, L-77, 408, and 806, increased the
level of disease incited by PST in ragweed (Ambrosia artemisiifolia),
dandelion (Taraxacum officinale), narrowleaf goldenrod (Solidago
tenuiifolia), and pitchforks (Bidens frondosa). While it was essential to
add an organosilicone at a rate of at least 0.2% v/v to bacterial
suspensions to incite disease in any of the species, the type of
organosilicone added was not a factor. Three applications of bacterial
suspension at 109 cfu/ml plus Silwet L-77 at 0.5% and applied one week
apart resulted in the death of dandelion and narrowleaf goldenrod plants.
PST survived exposure to much higher concentrations of Weedar 64 (2,4-D)
and Roundup Ultra (glyphosate) than any of the four weed species (J.
Porter and Bewick, MA). A combination of PST and Silwet L-77 can reduce
the effective rate of glyphosate needed for weed control (S. Boyetchko,
Canada).
Objective 1: Evaluation of Selected Pathogens as Bioherbicides
A Myrothecium sp. with broad host range has been discovered by D. Boyette
(MS) and L. Walker (LA). It was pathogenic to both common and horse
purslanes, and when applied with Silwet L-77, it was pathogenic to kudzu
(Pueraria lobata), a prolific weed. However, the potential for mycotoxin
production is a concern. Cotton is extremely sensitive to this fungus and
this trait may enable the fungus to be used as a biological defoliant for
cotton.
Dactylaria higginsii was evaluated for control of purple nutsedge (R.
Charudattan and E. Rosskopf, FL). Inoculum for trials was produced in
Charudattan's lab and field trials were conducted in watermelon,
sugarcane, and tomato crops. D. higginsii as an alternative to methyl
bromide, and its compatibility with different surfactants and chemical
pesticides are being examined. A similar program with Phomopsis
amaranthicola, a pathogen of pigweed, has also been initiated. Although
adjuvants such as Metamucil were capable of improved efficacy of D.
higginsii, more effort is needed to improve spore quality and
formulation. To this end, Sylvan (PA) and UAP (CO) will collaborate to
produce D. higginsii.
A mixture of fungal pathogens was tested to control weedy grasses, such as
cogongrass (Imperata cylindrica), a major invasive weed along roadways,
and in forests and abandoned lands. A similar "cocktail" of pathogens to
control waterhyacinth is also being developed. Ralstonia solanacearum
(=Pseudomonas solanacearum) was found to be an effective control agent for
tropical soda apple in Florida (R. Charudattan, FL). Colletotrichum
acutatum, a pathogen of dodder and cranberry and blueberry fruits, and a
Colletotrichum gloeosporioides were discovered by F. Caruso (MA). Since
the latter fungus did not affect the fruits, future efforts will focus on
this fungus. The following fungi are also being studied: Cercosporella
to control Russian knapweed (Acroptilon repens), Colletotrichum
gloeosporioides to control Russian thistle (Salsola australis) (W.
Bruckart, MD), and Sphaeropsis sp. for purple loosestrife (Lythrum
salicaria) (D. Johnson, MN). About 300 bacterial strains are being tested
as possible biocontrol agents of herbicide-resistant weeds. A bacterial
strain capable of survival in soil for over 2 months reduced the emergence
of wild oat (Avena fatua)(S. Boyetchko, Canada). A Fusarium sp. has been
found that could be integrated into crop-production systems. However, the
possibility of mycotoxin production is a concern (E. Rosskopf, FL).
Objective 2. Enhance the Efficacy of Bioherbicide Candidates
The effect of adjuvants in enhancing the efficacy of Cercospora rodmanii
and Myrothecium roridum, pathogens of the waterhyacinth (Eichhornia
crassipes) was evaluated. Application of these fungi with Metamucil and
Silwet L-77 as carriers enhanced the disease severity caused by the
fungi. A mixture of these fungi appeared to be mutually inhibitory. On
the other hand, the bioherbicide agents, Drechslera gigantea, Exserohilum
rostratum, and E. longirostratum were highly effective as a control for
guineagrass (Panicum maximum). A "cocktail" of these fungi, applied in
an emulsion developed by S. Yang (MD) was the most effective treatment
compared to each pathogen alone or all pathogens applied with water or
Metamucil as carriers (R. Charudattan, FL).
Objective 3. Develop Systems for Mycoherbicide Production and Formulation
In collaboration with Keith Howard (GA), experiments were initiated to
evaluate the persistence and efficacy of Colletotrichum truncatum (COLTRU)
microsclerotia incorporated in soil and stored under various soil
conditions. In addition, studies directed at reducing fermentation times
for production of microsclerotia were continued. Using the best
production method so far, the fermentation time was reduced from 10 days
to 6 days (M. Jackson, IL).
Efforts are underway to produce inoculum of Dichotomophthora portulacae, a
pathogen of Portulaca spp. Several solid and liquid media were tested,
including a variety of grains and sugarcane by-products; a satisfactory
method of production is yet to be found (E. Rosskopf, FL).
Water-dispersible granule (WDG) formulations containing a variety of
mycoherbicide agents are being developed. WDGs can stabilize propagules
of fungal pathogens and are easy to measure and apply by spraying after
dispersion in water. Other adjuvants are being investigated as means to
reduce the need for a prolonged dew-period (D. Daigle and W. Connick,
LA)..
Cooperative research on bioherbicide formulation is underway at ARS,
Stoneville, MS (D. Boyette), Agriculture and Agri-Food Canada, Saskatooon
(S. Boyetchko and K. Bailey), the ARS Narcotic Plant Project, MD, and the
dodder project (Bewick, MA). A 20-lb sample of Pesta formulation
containing Alternaria destruens, a pathogen of dodder, was prepared for
1999 field tests. A site-visit to Saskatoon was made by D. Daigle and W.
Connick (LA) to plan the research effort. An Organisation for Economic
Co-Operation and Development Fellowship was obtained by E. Rosskopf (FL)
to visit Dr. S. Boyetchko and to learn techniques for integrated weed
management approaches using deleterious rhizobacteria and foliar fungi.
L. Marshall, Trans America Product Technologies, MO, in cooperation with
J. Shearer (MS) has developed a biological carrier (BIOCAR) which is used
with the fungus Mycoleptodiscus terrestris, a bioherbicide agent for the
aquatic weed Hydrilla verticillata. The fungus encapsulated in tablets
has a shelf-life of 1.5 years under refrigeration. Formulation and
application hurdles have been overcome and a commercial partner is being
sought to market this bioherbicide agent.
Plans for Next Year:
Efforts will be made to optimize environmental conditions (aeration, pH,
and temperature) in deep-tank fermentation for rapid production of high
concentrations of microsclerotia. Studies will be continued to evaluate
the persistence of COLTRU microsclerotia stored in soil under various soil
conditions (M. Jackson, IL). Work will continue on developing
water-dispersible granules and adjuvants to reduce the dew-period
requirement. Pesta granular formulations of deleterious rhizobacteria and
various mycoherbicide agents will be prepared and evaluated under
cooperative research arrangements (states involved: FL, IL, LA, Canada,
and others).
Objective 4. Develop Genetic Characterization and Transformation of
Bioherbicide Candidates as a Means of Enhancing and Assessing
Environmental Risk
Techniques were developed to transform a fungus to induce enzymes that
help control Canada thistle (Cirsium arvense) (K. Bailey, Canada). Mutant
strains of Colletotrichum gloeosporioides f.sp. aeschynomene (the Collego
pathogen) were produced and tested. The mutants were not to be as
competitive as the wild type (D. TeBeest, AR).
PUBLICATIONS
Abbas, H.K., and Paul, R.N. 1998. Ultrastructural effects of AAL-toxin from
the fungus Alternaria alternata on black nightshade (Solanum nigrum)
leaf discs and correlation with biochemical measures of phytotoxixcity.
Toxicon 36:1821-1832.
Bailey, B.A., Hebbar, K.P., Strem, M.D., Darlington, L.C., Connick, W.J., Jr.,
Daigle, D.J. and Lumsden, R.D. 1998. Formulations of Fusarium
oxysporum f. sp. erythroxyli for biocontrol of Erythroxylum coca var.
coca. Weed Sci. 46:682-689.
Berner, D. K., N.W. Schaad, and B. Volksch. Selection of ethlene-producing
bacteria for stimulation of Striga spp. seed germination. Biological
Control. 1999. In Press.
Bianco, S., Pitelli, R.A., Bellingieri, P.A, Mullahey, J.J., and Charudattan,
R. 1998. Growth and nutrient uptake by tropical soda apple (Solanum
viarum Dunal). WSSA Abstracts. 38:21.
Chandramohan, S., and Charudattan, R. 1998. A technique for mass production
and multiple-harvesting of two bioherbicide fungi by solid-substrate
culturing. WSSA Abstracts. 38:81.
Chandramohan, S. and Charudattan, R. 1998. Host-Specific Response of
Pathogens in a Mixture on Different Weed Hosts: an Electron Microscopic
Study. Phytopathology 88 (Suppl.):S15.
Chandramohan, Charudattan, R., Sonoda, R.M., and Singh, M. 1999. Field tests
of a pathogen mixture for bioherbicidal control of guineagrass (Panicum
maximum Jacq.). WSSA Abstracts 39:75.
Charudattan, R. 1998. Experience on water hyacinth control in USA. Pages
47-51. Anonymous eds., in: Reunion Regional Sobre Control Integrado
del Lirio Acuatico. Instituto Mexicano de Technologia del Agua,
Cuernavaca, Mexico. Nov. 24-28, 1997. Organizacion de la Alimentacion y
la Agricultura de las Naciones Unidas, FAO, Roma.
Cisar, C.R. and D.O. TeBeest. 1999. Mating system of the filamentous
ascomycete, Glomerella cingulata. Current Genetics. (Accepted for
publication Nov. 21, 1998).
Connick, W.J., Jr., Daigle, D.J., Pepperman, A.B., Hebbar, K.P. Lumsden, R.D.,
Anderson, T.W. and Sands, D.C. 1998. Preparation of stable, granular
formulations containing Fusarium oxysporum pathogenic to narcotic
plants. Biol. Control. 13:79-84.
Daigle, D.J., Connick, W.J., Jr., Boyette, C.D., Jackson, M.A., and Dorner,
J.W. 1998. Solid-state fermentation plus extrusion to make
biopesticide granules. Biotechnol. Tech. 12:715-719.
Daigle, D.J. and Lumsden, R.D. 1998. Formulations of Fusarium oxysporum f. sp.
erythroxyli for biocontrol of Erythroxylum coca var. coca. Weed Sci.
46:682-689.
DeValerio, J.T. and Charudattan, R. 1999. Field testing of Ralstonia
solanacearum [Smith] Yabuuchi et al. as a biocontrol agent for
tropical soda apple (Solanum viarum Dunal). WSSA Abstracts 39:70.
Elwakil, M.A., Shabana, Y.M., Charudattan, R., Baka, Z.A.M., Abdel-Fattah, G.M.
1998. Development of Alternaria eichhorniae for biological control of
waterhyacinth in Egypt. In: M.H. Belal, V. Beyssat-Arnaouty, and S.A.
El Arnaouty, Eds. Proceedings of Regional Symposium for Applied
Biological Control in Mediterranean Countries, Oct. 25-29, 1998, Cairo,
Egypt. Center of Biological Control, Faculty of Agriculture, Cairo
University, Cairo, Egypt.
Fravel, D.R., Connick, W.J., Jr. and Lewis, J.R. 1998. Formulation of
microorganisms to control plant diseases, in Formulation of Microbial
Biopesticides, Beneficial Microorganisms, Nematodes and Seed
Treatments (Burges, H.D., Ed.), Chapman and Hall, London, pp. 187-202.
Isaccson, D.L. and Charudattan, R. 1999. Biological control of weeds. Pages
xxx-xxx In: Handbook of Pest Management, J.R. Ruberson, ed. Marcel
Dekker, New York.
Jackson, M.A., J.S. Frymier, B.J. Wilkinson, P. Zorner and S. Evans. 1998.
Growth Requirements for the Production of Stable Cells of the
Bioherbicidal Bacterium Xanthomonas campestris. J. Ind. Microbiol.
21:237-241.
Jackson, M.A., D.A. Schisler, C.D. Boyette, W.J. Connick, Jr. and N.K. Zidack.
1998. Improving Mycoherbicide Fitness using Nutrition Management during
Production and Formulation. British Mycological Society Symposium "The
Future of Fungi in the Control of Pests, Weeds and Diseases",
Southampton, United Kingdom. P.37.
Kadir, J. and Charudattan, R. 1998. Factors affecting the efficacy of
Dactylaria higginsii (Luttrell) M.B. Ellis as a bioherbicide for
control of purple nutsedge (Cyperus rotundus L.). WSSA Abstracts.
38:45.
Luo, Y. and D.O. TeBeest. 1998. Behavior of a wild-type and two mutant
strains of Colletotrichum gloeosporioides f.sp. aeschynomene on
northern jointvetch in the field. Plant Disease 82:374-379.
Luo, Y. and D.O. TeBeest. 1998. Effect of temperature and dew period on
infection of northern jointvetch by wild-type and mutant strains of
Colletotrichum gloeosporioides f.sp. aeschynomene. Biological Control
14: 1-6.
Martinez Jimenez, M., and Charudattan, R. 1998. Survey and evaluation of
Mexican native fungi for biocontrol of waterhyacinth. J. Aquat. Plant
Manage. 36:145-148.
McGuire, M.R., Connick, W.J., Jr., and Quimby, P.C., Jr. 1998. Formulation
of microbial pesticides, in Controlled Release Pesticides (Scher, H.B.,
Ed.), Marcel Dekker, New York. Accepted 6/27/97.
Pereira, W., Charudattan, R., and Kadir, J. 1998. Susceptibility of purple
nutsedge (Cyperus rotundus) accessions to Dactylaria higginsii
(Lutrell) M.B. Ellis. WSSA Abstracts. 38:45.
Pitelli, R.A., Charudattan, R., and DeValerio, J.T. 1998. Effect of Alternaria
cassiae, Pseudocercospora nigricans, and soybean (Glycine max) planting
density on the biological control of sicklepod (Senna obtusifolia).
Weed Technol. 12:37-40.
Quimby, P.C., Jr., Zidak, N., Boyette, C.D., and Grey, W. P. A method for
stabilizing and granulating Microbial biological control agents.
Biocontrol Sci. and Tech. (In press).
Rosskopf, E.N. 1998. Evaluation of Phomopsis amaranthicola sp. nov. as a
biological control agent for Amaranthus spp. Ph.D. dissertation.,
Univ. of FL, Gainesville, FL. 190 pp.
Rosskopf, E.N., Charudattan, R., and Kadir, J.B. 1999. Use of Plant Pathogens
in Weed Control. Pp. 891-918, in: T.W. Fisher and T.S. Bellows, eds.
Handbook of Biological Control. Academic Press, New York, New York.
In press.
Shabana, Y.M., Cuda, J.P., Charudattan, R. 1998. Integrated control of
Hydrilla verticillata with fungal and insect biocontrol agents.
Phytopathology 88 (Suppl.):S80.
Shabana, Y.M., Elwakil, M.A., and Charudattan, R. 1998. Status and progress
of biological control of waterhyacinth, Eichhornia crassipes, in Egypt.
Abstracts, 7th Int. Congr. Plant Pathol., Edinburgh, Scotland. Abstr.
No. 5.2.41.
Smither-Kopperl, M.L., Charudattan, R., Berger, R.D. 1998. A model system to
investigate the spread of Plectosporium tabacinum disease on hydrilla.
Phytopathology 88 (Suppl.):S83.
Smither-Kopperl, M.L., Charudattan, R., and Berger, R.D. 1998. Dispersal of
spores of Fusarium culmorum in aquatic systems. Phytopathology
88:382-388.
Smither-Kopperl, M.L., Charudattan, R., and Berger, R.D. 1999. Plectosporium
tabacinum, a pathogen of the invasive aquatic weed Hydrilla
verticillata in Florida. Plant Dis. 83:24-28.
Tessmann, D.J. and Charudattan, R. 1998. Pathogenic variability of Cercospora
piaropi and C. piaropi on waterhyacinth (Eichhornia crassipes). WSSA
Abstracts. 38:79.
Tessmann, D.J., Charudattan, R., Kistler, H.C. 1998. A molecular
characterization of Cercospora species pathogenic to waterhyacinth
(Eichhornia crassipes) based on three conserved genes. Phytopathology
88 (Suppl.):S88.
Vincent, A.C. and Charudattan, R. 1999. Effects of formulations of
Myrothecium roridum Tode ex. Fr. and Cercospora rodmanii Conway on
waterhyacinth (Eichhornia crassipes [Mart.] Solms-Laub.) Under
greenhouse and field conditions. WSSA Abstracts 39:71.
Wyss, G.S., Henkel, T., Charudattan, R., and DeValerio, J.T. 1999.
Mass-production of conidia of Dactylaria higginsii (Luttrell) M.B.
Ellis, a potential biocontrol agent for nutsedges (Cyperus spp.) on
natural and synthetic media and grains. WSSA Abstracts 39:74.
Yandoc, C.B., Chandramohan, S., Charudattan, R., and Shilling, D.G. 1998.
Evaluation of fungal isolates for their potential as biological control
agents for cogongrass [Imperata cylindrica (L.) Beauv.]. WSSA
Abstracts. 38:45.
Yandoc, C. and Charudattan, R. 1998. Use of natural substrates for the
production of fungal inoculum for biological weed control studies.
WSSA Abstracts. 38:80.
Yandoc, C.B., Charudattan, R., and Shilling, D.G. 1999. Enhancement of
efficacy of Bipolaris sacchari (E. Butler) Shoem., a bioherbicide
agent of cogongrass [Imperata cylindrica (L.) Beauv.], with adjuvants.
WSSA Abstracts 39:72.
Yang, S-M, Dowler, W.M., Schaad, N.W. and Connick, W.J., JR. 1998. Combined
carrier and weakly virulent or non-virulent plant pathogens to control
weeds. U.S. Patent No. 5,795,845
PREPARED BY:
__________________________________________ _________________________
Project Chairman Date
APPROVED:
__________________________________________ _________________________
Administrative Advisor Date
APPENDIX
REPORTS FROM PARTICIPANTS
ARKANSAS
D.O. TeBeest
Dept. Plant Pathology, Univ. of Arkansas, Fayetteville, AR 72701;
TEL: 501-575-2445; FAX: 501-575-7601
E-mail: Dtebeest@comp.uark.edu
OBJECTIVE 1: Evaluate selected pathogens as bioherbicides.
A pathogen of an important grass weed has been found from literature
references and a selection of isolates that produce spores in culture in
plate culture on several media have been obtained. Preliminary tests
indicate virulence to at least one crop species.
In 1998, a formulation of spores of C. gloeosporioides f.sp. aeschynomene
was again made commercially available as COLLEGO to rice producers to
control northern jointvetch in rice in Arkansas. All available product
distributed by Encore Technologies, Minnetonka, MN. was distributed, sold
and used without complaint in what is considered a hot, dry year. The new
formulation appeared to work as well as or better than the formulations
used earlier.
A method has been worked out which will permit the evaluation and
selection of multiple strains for competitive ability in the field. A
portion of this work has been published.
OBJECTIVE 2: Enhance the efficacy of bioherbicide candidates.
Successful biological control often requires the proper selection and
matching of isolates to environmental conditions that permit epidemics to
develop after application of inoculum. However, little work has been
conducted on post inoculation epidemiology and on methodologies that test
the interactive competitiveness of isolates under field conditions. Since
the effectiveness of COLLEGO depends on post inoculation increase of
disease, research in 1998 emphasized and tested inter-strain competition
of wild-type and mutant isolates of C. gloeosporioides. Results of
inter-strain competition field tests indicated that benomyl resistant and
nitrate non-utilizing strains of C. gloeosporioides were not as
competitive as the wild-type isolate when co-inoculated on northern
jointvetch.
Research conducted in the controlled environment facilities at the
University of Arkansas suggest that there were small but significant
changes in several of the disease components related to infection of
northern jointvetch by mutant strains. Lesion extension, latent period
and sporulation were reduced in mutant strains. These factors, in
concert, reduced the ability of the mutant strains to cause and sustain
epidemics in competition with the wild type, reducing their capacity to
survive within a heterogenous population and cause disease.
OBJECTIVE 4: Develop genetic characterization and transformation of
bioherbicide candidates as a means of enhancing and assessing
environmental risk.
We previously reported that isolates of Colletotrichum gloeosporioides
including C. gloeosporioides f.sp. aeschynomene were mating compatible.
Fertile perithecia were produced in all-way crosses of isolates virulent
to apple (pecan), mango, papaya, alfalfa, northern jointvetch and winged
water primrose. Research was conducted in 1998 to better describe the
mating system of Colletotrichum gloeosporioides to help us understand the
potential dynamics of gene flow within this very large and diverse
species.
Mating in heterothallic filamentous ascomycetes is typically controlled by
a single mating type locus with two alternate alleles or idiomorphs. In
our studies to clarify the system, five self-sterile strains of C.
gloeosporioides (Glomerella cingulata) virulent to pecan were crossed in
all possible combinations. Four of the five strains could be placed into
two mating type groups, but the fifth isolate was sexually compatible with
all of the other strains tested. Single ascospore progeny were isolated
from each of the successful crosses, tested for self-fertility and
back-crossed with both parents. In addition, subsets of F1 isolates were
crossed with all five of the original strains from pecan and all possible
combinations with each other. Results of the crosses showed that the
ascospore progeny had stabley inherited the mating pattern of one of the
parental strains and that mating type had segregated 1:1 among the F1
isolates. Furthermore, all five strains from pecan wee sexually
compatible with five additional heterothallic strains (see above) in all
but one combination. Data from these experiments are consistent with a
mating system composed of a single mating type locus with multiple
alternate alleles mating alleles (single locus, multiple alleles). We
believe that this is the first report of a mating systems of this type for
an ascomycete species.
USEFULNESS / APPLICATION OF THE FINDINGS: Several biological herbicides
are in reality not "herbicides" not at all but rather epidemics. The
application of inoculum--by any method---results in a few lesions on
targeted plants. Control of the weed results from the ensuing development
of many more lesions. The rapid increase of disease is an epidemic, thus,
control results from the epidemic caused by the initial inoculation.
In the case of COLLEGO, for example, results reported this year are based
on two facts. First, control of northern jointvetch in these experiments
results from the rapid increase of disease from as few as 1 to 5 lesions
per plant. Second, the increase of disease is based on the disease cycle;
infection, lesion extension, sporulation, dissemination followed by re-
infection of the host. In this system, we have found that the most
competitive strains are those that efficiently produce lesions, they
produce lesions in a very short time, they sporulate profusely on lesions
and lesions grow rapidly. In this kind of bioherbicide or pathosystem, an
effective strain may most easily be discerned from all others by setting
up competition between strains and selecting those that predominate within
the growing population. These strains are marketable and effective.
Also in the case of COLLEGO, we can now generate transgenic strains by
recombinant DNA techniques and hybrid strains by a simple breeding
program. However, we have been given cause to rethink the developmental
strategies and potential release of transgenic or even hybrid strains. We
now know that we can create hybrid strains of many Colletotrichum species,
especially C. gloeosporioides, because we have, through recurrent
backcrosses and selection, created hybrid strains of C. gloeosporioides
virulent to northern jointvetch, pecan and apple but of opposite mating
type to either parental isolate. A mating type allele was "moved" from
one special form to another in the process. These new hybrids are
genetically capable of crossing in the field with either parental form
during the growing season.
Combining the epidemic capacity for these bioherbicides with the genetic
interactions has some potential impact on developing and releasing
sexually compatible strains of these fungi.
WORK PLANNED FOR NEXT YEAR:
Objective 1: We will continue to work with the pathogen of grasses in an
effort to better describe the host range of this species, to better define
the environmental conditions and spore concentrations needed for control
of the targeted host.
Objective 2: We will conduct experiments in 1999 to better define the
effect of various pesticides on the efficacy of Collego. We will test the
ability of specific adjuvants to modify and/or increase the targeted host
range of this successful biological control agent.
Objective 3: No work is planned for this objective.
Objective 4: We will resume a project which will look at the segregation
of virulence characteristics of over 800 progeny from a series of
backcrosses of Collego with an apple isolate to gain a better
understanding of the inheritance of virulence in this pathogen.
Publications:
Cisar, C.R. and D.O. TeBeest. 1999. Mating system of the filamentous
ascomycete, Glomerella cingulata. Current Genetics. (Accepted for
publication Nov. 21, 1998).
Luo, Y. and D.O. TeBeest. 1998. Behavior of a wild-type and two mutant
strains of Colletotrichum gloeosporioides f.sp. aeschynomene on
northern jointvetch in the field. Plant Disease 82:374-379.
Luo, Y. and D.O. TeBeest. 1998. Effect of temperature and dew period on
infection of northern jointvetch by wild-type and mutant strains of
Colletotrichum gloeosporioides f.sp. aeschynomene. Biological
Control 14: 1-6.
FLORIDA
R. Charudattan, S. Chandramohan, J.T. DeValerio, M. Smither-Kopperl,
D. Tessmann, A. Vincent, G. Wyss, C. Yandoc
Biological Control of Weeds Lab., Plant Pathology Dept., Univ. of Florida,
Gainesville, FL 32611-0680;
TEL: 352-392-7240; FAX: 352-392-6532; E-mail: rc@gnv.ifas.ufl.edu
OBJECTIVE 1: Evaluate selected pathogens as bioherbicides.
Four fungal isolates, a Cephalosporium sp., an unidentified fungus, a
Botrytis sp., Fusarium culmorum, and Plectosporium tabacinum, recovered from
hydrilla shoots or from soil and water surrounding hydrilla in ponds and
lakes in Florida, were capable of killing hydrilla in a test-tube bioassay.
The isolates were tested at 6 x 104 to 1 x 106 conidia per ml, singly and in
combination with the leaf-mining fly, Hydrellia pakistanae (Diptera:
Ephydridae) (HP), for their ability to kill or damage hydrilla in the
test-tube assay. The insects were used at two levels to yield 15 and 25 %
shoot damage. F. culmorum, the most effective isolate, was examined further
in an aquarium test. For the fungus+insect treatments, hydrilla shoots were
inoculated with F. culmorum (1x106 conidia per ml) at two levels of insect
damage (15 % and 25 %) at the time of inoculation (11 and 28 days,
respectively, after HP establishment). The interaction of F. culmorum and HP
resulted in a higher level of damage on hydrilla shoot (76 to 98 %) compared
to that caused by each agent alone (24 and 35%) for the two HP levels and 63
% for the fungus alone). Maximum shoot kill was achieved at 20-30 C compared
to 15 or 35 C. Thus, it may be possible to integrate fungal and insect
agents to control hydrilla.
Sixty isolates of Cercospora species pathogenic to waterhyacinth, Eichhornia
crassipes, collected from the United States, Mexico, Venezuela, Brazil, South
Africa and Zambia, were screened in a quarantine greenhouse in Gainesville to
assess the variability in their virulence. A bioassay was used which
consisted of immersing waterhyacinth leaves, attached to plants, in a
suspension of inoculum. The inoculum was prepared from mycelium grown in
still liquid cultures in V8 medium for 14 days at 25 3 C. The mycelium was
separated from broth by filtration and blended for 5 sec at a concentration
of 80 mg/ml of water. The suspension was amended with 0.5% Metamucil and
0.05% Silwet . Four replicates, each with one 2-leaved plant, were used and
the experiment was done twice. The treatments were arranged in a randomized
complete block design. Control leaves were immersed in a solution containing
only the amendments. The inoculated and control plants were placed in a dark
dew chamber at 25 2 C for 12 h and then held in a greenhouse for 2 wk.
Disease severity was assessed 4, 7, and 14 days after inoculation using a
visual rating scale of 0-7. The isolates differed significantly in virulence
(P<0.05), varying from being nonvirulent (rating 0) to highly virulent
(rating 7, leaf death). The variation in virulence among the isolates was
independent of their geographic origin, spore size or cultural differences.
Eleven fungal isolates from various grassy weeds species were tested in the
greenhouse for their pathogenicity to cogongrass, Imperata cylindrica.
Fungal spores or mycelial fragments were applied inundatively on 3- to
5-wk-old cogongrass plants in pots. Spores were suspended in 1% gelatin
solution or in a 0.5 % Metamucil suspension and applied at the rate of 104 to
106 spores/ml with a hand sprayer. Mycelial fragments of nonsporulating
cultures, prepared by blending liquid-culture-grown mycelia, were suspended
in 0.5 % Metamucil (1 g mycelia/ml) and applied onto leaves with a sterile
paintbrush. Inoculated plants and appropriate controls were incubated in a
dark dew chamber for 24 h at 28 + 1 C. The test plants were then kept in a
greenhouse and disease severity was assessed 7 days after inoculation. A
pictorial disease assessment key with 50% as the maximum value was used. The
pathogenicity tests were done at least twice and diseased tissues were
routinely collected and plated on PDA medium to reisolate the causal organism
and fulfill the Koch's postulates. The various isolates caused infections
resulting in mere speckling of the leaves to leaf blights. Two fungal
isolates, Exserohilum longirostratum from crowfootgrass (Dactyloctenium
aegyptium) and Exserohilum rostratum from johnsongrass (Sorghum halapense),
caused leaf spots and leaf lesions. Disease severity on cogongrass treated
with 105 spores/ml of E. longirostratum was 10%. Plants treated with 104
spores/ml of E. rostratum had 5% disease severity. Disease severity in
plants treated with a Drechslera sp. from cogongrass and Drechslera gigantea
from large crabgrass (Digitaria sanguinalis) ranged from 30-40% and the
symptoms consisted of discrete and coalescent leaf lesions and leaf blights.
These isolates are currently being tested for their efficacy in greenhouse
and miniplot trials.
Three fungi native to Florida were field-tested for their ability to control
populations of guineagrass Panicum maximum. The plots (1 m2) were arranged
in a completely randomized factorial design and the experiment was done
twice: Fall 1996 and Spring 1998. The guineagrass plants within each plot
were inoculated with spore suspensions of Drechslera gigantea, Exserohilum
rostratum, or E. longirostratum, isolated respectively from large crabgrass,
johnsongrass, and crowfootgrass, or a mixture of all three pathogens (1:1:1
by vol). The fungi were applied as foliar sprays, each containing 5x105
spores per ml in water, 0.5% aqueous Metamucil, or an emulsion (Sunspray 6E,
SUNOCO). The carriers alone were included as controls. A second application
of treatments was done 2 wk after the initial spray. Disease severity (DS)
was recorded weekly for 4-6 wk after the initial spray. In both trials, DS
levels from the emulsion-inoculum treatments were higher than from the other
two carrier-inoculum treatments. DS from the emulsion- inoculum treatments
increased significantly after the second application and reached the maximum
2 wk later. The maximum DS levels from the emulsion-inoculum treatments of
individual or mixture of fungal spores were 93.8-98.5% (1996) and 96.1-98.0%
(1998) compared to 1.5-7.25% (1996) and 9.0-18.5% (1998) from the
water-inoculum, and 4.88-9.13% (1996) and 28.0-32.8% (1998) from the
Metamucil- inoculum. Thus, effective control of guineagrass could be
obtained under field conditions with an emulsion- based inoculum
preparation.
Certain strains of Ralstonia solanacearum (=Pseudomonas solanacearum; RS)
are highly pathogenic to tropical soda apple (TSA), a pasture weed. Since
mowing is used for TSA control, a post-mowing application of RS is considered
a rational method of field testing this bacterium. Initial trials were done
on 187-day-old, 0.6-m-tall containerized (11.4 L) plants by clipping the main
stem 3 cm above the soil and swabbing the cut surface with a 1-day-old
bacterial suspension. The inoculum was applied at two rates, 1.74 and 0.74
absorbance units (AU) at 600 nm. A water control was included, and there were
5 replicates. By 12 weeks, 100% of the plants treated with the high inoculum
level were killed and the shoot biomass was reduced in the low inoculum level
treatment. Two field trials were then established in Sumter and Levy
Counties, Florida, using a completely random design with 30 and 20 replicates
per treatment, respectively. One-day-old inoculum was used at two rates:
1.04 AU (low rate, Sumter) and 1.96 AU (high rate, Levy). The Sumter site
was in a pasture under full sunlight; the Levy site was under partial shade
in an oak hammock. Treatments and results after 2 weeks for the Sumter and
Levy sites were, respectively: injected- inoculated, 96% and 11% healthy;
injected-control, 100% and 45% healthy; cut and swabbed-inoculated, 13% and
10% resprouting; and cut and swabbed-control, 92% and 30% resprouting. RS was
more effective at the Levy site where the plants were shaded and smaller and
higher inoculum level was used. RS applied as a post-cut treatment is an
effective method of control for TSA under field conditions.
OBJECTIVE 2: Enhance the efficacy of bioherbicide candidates.
A mixture of pathogens consisting of four fungi, namely Alternaria cassiae
(AC; major host, sicklepod [Senna obtusifolia]; alternative host, showy
crotalaria [Crotalaria spectabilis]), Colletotrichum dematium f.sp.
crotalariae, and Fusarium udum f.sp. crotalariae (CD and FU; pathogens of
showy crotalaria), and Phomopsis amaranthicola (PA; pathogen of pigweed
[Amaranthus hybridus]), was tested for interactions of the pathogens with
their respective hosts and nonhosts. A spore suspension of each pathogen
alone (106 per ml) and a cocktail of the four pathogens (1:1:1:1 by vol)
containing 106 spores per ml of each were sprayed to runoff on the weed
seedlings grown together in pots. The inoculum suspensions and the water
control were amended with 0.5 percent Metamucil, a humectant. The seedlings
were inoculated, given 12 h of dew at 28 C and held in a greenhouse for 8
weeks. Samples of leaf tissues from all treatments were processed and
examined with a scanning electron microscope. The leaf surface of each weed
host was predominantly occupied by spores of its respective host-specific
pathogen. AC caused extensive tissue maceration and rarely formed
appressoria on its major host, sicklepod. It formed healthy germ tubes and
multiple appressoria without any associated tissue maceration on showy
crotalaria, its alternative host. Appressoria of AC lysed on pigweed, a
nonhost. CD formed healthy appressoria on showy crotalaria, while either
appressorial lysis and/or poorly formed appressoria were observed on the
nonhosts sicklepod and pigweed. PA germinated and grew only on pigweed,
while it did not grow on sicklepod or showy crotalaria. FU, although a
root-pathogen, germinated and grew on showy crotalaria leaves, but not on
leaves of its nonhosts. The developmental patterns of the pathogens appear
to be conditioned by specific interactions with the host leaf surface,
whether the pathogens were applied alone or in a mixture. It is feasible to
use several pathogens simultaneously to control several weeds without loss of
host-specificity of each pathogen.
Dactylaria higginsii, a fungal pathogen, is being examined as a potential
bioherbicide for control of purple nutsedge. In controlled environments, it
required a minimum dew period of 12 h and a temperature of 25 C during the
dew period to produce severe disease on 4- and 6-leaf-stage plants inoculated
with 106 conidia/ml. Under these conditions, 75% disease (percent leaf area
damaged) and excellent weed control were achieved. Interaction between
dew-period temperature, dew-period duration and plant growth stages indicated
that younger plants (4-to 6-leaf) were more susceptible to D. higginsii
compared to mature plants (8-leaf-stage plants or older). At the optimum
dew-period duration and dew-period temperature (24 h and 30 C, respectively),
the number of days to obtain 50% disease severity on 4- and 6-leaf-stage
plants was significantly less (10 days) compared to older plants (16 days).
These results indicated that to achieve effective control, D. higginsii
should be applied early in the growing season when purple nutsedge plants are
young and optimal temperature and dew periods are not limiting.
Formulations of two fungal pathogens were evaluated in greenhouse and field
trials for their effects on waterhyacinth. Mycelial fragments (Cercospora
rodmanii; 0.08g/ml) or spores (Myrothecium roridum; 106- 108/ml) were used as
inoculum that was sprayed onto waterhyacinth plants (6- to 8- leaf stage)
maintained in 4-L containers. For inoculum production, the fungi were grown
on V8 broth in Roux bottles (C. rodmanii) or on potato dextrose agar in petri
plates (M. roridum). The inoculum was prepared in the following carriers:
sterile water, Metamucil (0.5%), Silwet L-77 (0.05%), Metamucil + Silwet, or
an oil emulsion (5% 5 ml Sunspray 6E, 45 ml light mineral oil, and 50 ml
water). The fungi were tested singly or in combination. The treatments were
applied with hand sprayers and appropriate controls were maintained. A
completely randomized design with three replicates was used. Each trial was
repeated at least twice. Disease severity (DS) was assessed 4 days after
inoculation and every 3 to 4 days thereafter for 6 weeks on a 0-9 scale with
a pictorial disease assessment key. At 6 weeks, the two fungi produced
similar levels of DS. Myrothecium + Silwet produced the highest DS of any
treatment. Cercospora + Metamucil and Cercospora + Metamucil + Silwet were
equally effective, while Cercospora + Metamucil + Silwet and Cercospora + oil
emulsion produced the next highest DS followed by Cercospora + Silwet and
Cercospora + sterile water. When applied together in a cocktail, the fungi
appeared to be mutually inhibitory. This may be due to the production of
antifungal metabolites or competition for infection sites on the leaf surface
by these fungi.
The suitability of oil emulsions and gelatin to enhance the biocontrol
efficacy of B. sacchari was evaluated in greenhouse tests. Spores in sterile
water (105 /ml) were mixed with equal volumes of 2% gelatin, 8% oil emulsion
(8 ml Sunspray 6E, 72 ml water, and 20 ml mineral oil), and 80% oil emulsion
(80 ml Sunspray 6E and 20 ml mineral oil) to achieve final concentrations of
1% gelatin and 4% and 40% oil emulsions. Cogongrass plants (3- to 6-leaf
stage; 5 weeks after sowing) were sprayed with the spore-adjuvant mixtures
and the adjuvants alone and exposed to 24 h of dew at 27+1 C. Treated plants
were assessed for foliar disease or phytotoxic damage using a pictorial key
with 50% disease/damage as the maximum. The 40% oil emulsion, with or without
spores, caused a 100% weed mortality (WM). The 4% oil emulsion alone was
less phytotoxic and caused 28.5% WM. The 4% oil emulsion + spores caused
severe bighting (50% disease severity [DS]) and 96% WM. There was no
phytotoxicity from 1% gelatin alone, while the gelatin + spore treatment
yielded 27.4% DS and 0% WM after 3 weeks. Treatment with oil emulsion +
spores and gelatin + spores at five dew periods (0, 4, 8, 12, and 24 h)
resulted respectively in 42.4% DS and 48.8% WM and 18.8% DS and 0% WM
(averaged over all dew treatments). Dew period and adjuvant type
significantly affected disease (p=0.05). Based on DS and WM ratings and the
ability to reduce inoculum run-off, the 4% oil emulsion was most effective in
enhancing the biocontrol efficacy of B. sacchari.
OBJECTIVE 3: Develop systems for mass-production of stable bioherbicide formulations.
Spores of two bioherbicide agents (Drechslera gigantea and Exserohilum
rostratum) were produced on a solid-substrate medium. Mycelial plugs (1-wk
old) were used to inoculate 1000 ml V8 broth in 2-L flasks. The inoculated
flasks were shake-cultured (100 rpm) for 2-3 days at 25oC. The contents of
each flask plus 10 ml of an antibiotic solution (3.7 mg/ml streptomycin and
2.5 mg/ml chloramphenicol) were blended in a Waring blender at low speed for
30-60 sec and 500 ml of this suspension was poured onto a layer of V8 agar
(500 ml) containing antibiotics (as above) in trays (37.5x30x1.25 cm) lined
with aluminum foil. The trays were exposed to alternating light and dark
cycles (12 h per cycle) at room temperature. The initial crop of spores
appeared within 24 h. These spores were collected in two steps: first, the
spores were gently scraped-off with a rubber spatula into sterile water. The
remaining spores were then rinsed-off the agar surface with sterile water.
The spore suspensions were pooled and the spores were allowed to settle
down. The excess supernatant was decanted and the spores were resuspended in
250 ml sterile water. The trays were reincubated under light as before and
the spores were harvested twice at 24 h and 48 h. The spore yields for D.
gigantea and E. rostratum averaged 2.05x105, 3.43x105, and 1.89x105, and
2.44x105, 2.16x105, and 1.00x105 spores/ml/harvest, respectively. Thus, it
is feasible to mass produce these fungi by solid-substrate culturing and
multiple spore harvests.
Screening fungal pathogens for their potential as biological control agents
for weeds requires a steady supply of ample and viable inocula, usually
spores, to carry out greenhouse and field trials. Biological control
candidates, mostly fungi, have been routinely cultured in agar media in petri
plates, a method that is not suitable for mass production of inocula. The
suitability of natural substrates to support vigorous growth and abundant
sporulation of two fungi was evaluated in the laboratory. Sorghum and oat
grains in flasks were autoclaved twice (at 121 C for 20 min each time) and
inoculated with blended mycelia of two species of Drechslera isolated from
cogongrass and large crabgrass. Cultures were incubated at 26 C with
alternating light and dark periods (12 h each). Both substrates yielded
spores after 2 wk. Twenty five grams of grains yielded 100 ml of suspension
with 105 to 106 spores/ml. The isolates produced more spores in oats (106
spores/ml) than in sorghum (105 spores/ml), (p=0.05). Inoculations in the
greenhouse showed that spores harvested from the grains were as infective as
the spores grown on V8 plates. Mass production of inoculum may be achieved
by using larger amounts of grains and inoculating with an appropriate volume
of blended mycelia as seed inoculum.
Experiments were carried out to determine an efficient, quick and inexpensive
method of mass-production of inoculum of D. higginsii for field trials.
Various natural (potato-dextrose agar [PDA], PDA with yeast extract, PDA with
nutsedge leaf extract, malt and yeast extracts, V8 agar, cornmeal agar and
oatmeal agar) and synthetic media (modified Sabouraud's agar, modified
Sabouraud's and NaCl, Czapek-Dox agar, Sach's agar, and Sanderson and Serb
medium) were prepared in petri dishes. There were four replicate plates per
medium. The plates were inoculated centrally with an agar plug from
13-day-old cultures, randomized and incubated in a growth chamber at 26 C and
12 h photoperiod at 40 E/m2/s. Colony diameter over time and conidial
production were measured. Three types of rice media in Erlenmeyer flasks were
compared (white Basmati rice [WR], WR with nutsedge leaves [+NSL] and brown
rice [BR]). They were inoculated with three agar plugs per flask and kept
under the same conditions as above. Four flasks per treatment were harvested
every second day for 21 days and conidial production was determined. Colony
diameter was largest on oatmeal agar and generally higher on natural media
compared to synthetic media. Conidiation was uniformly poor on synthetic
media and highest on PDA. The addition of nutsedge leaf extract increased
spore production in one experiment. In contrast, yeast extract seemed to
inhibit spore production. In the case of rice media, spore production was
higher on WR compared to BR. Generally, the peak spore production occurred as
early as four days after inoculation on WR (1x106 spores/ml; 30 g of WR) but
could be delayed up to 10 days after inoculation on WR+NSL (2.5x106
spores/ml). In conclusion, although colony development was similar on natural
media, spore production on these media varied and was generally poorer
compared to production on WR. WR with addition of NSL was the most productive
medium for rapid and inexpensive inoculum production.
OBJECTIVE 4: Develop genetic characterization and transformation of
bioherbicide candidates as a means of enhancing and assessing environmental
risk.
Two Cercospora species have been studied as biocontrol agents of the aquatic
weed waterhyacinth: C. piaropi described by Tharp in 1917 from a Texas
specimen and C. rodmanii described by Conway in 1976 from a Florida
specimen. These species were differentiated on the basis of their disease
severity on waterhyacinth and conidial size and morphology, but it is not
easy to distinguish them in practice. To test if the cladistic species
concept agrees with the morphological/ecological species concept, 14 isolates
of Cercospora spp. obtained from symptomatic waterhyacinth leaves collected
in the USA (Florida and Texas), Mexico, Venezuela, Brazil, South Africa, and
Zambia were compared on the basis of the DNA sequence of gene segments for
beta-tubulin (TUB2), histone-3 (H3), and elongation factor-1-alpha (EF1 ),
corresponding to 380, 309, and 431 base pairs (bp), respectively. Eight of
the isolates were also compared for the rDNA regions containing ITS1, ITS2,
and the 5.8S gene. Extracted DNA was amplified by PCR using TUB2, H3, and
ITS primer pairs selected from the literature. The EF1 primer pair was
designed by us for this study. In the rDNA region spanning ITS1, 5.8S, and
ITS2, 563 bp were invariant even when compared with C. beticola as the
outgroup. Using parsimony, the combined phylogenetic analysis of TUB2, H3,
and EF1 sequences done with PAUP (Phylogenetic Analysis Using Parsimony) did
not support the species distinction between C. piaropi and C. rodmanii.
Isolates of both species were placed together in the same, well-supported
clade compared to the outgroup.
The ability to distinguish biotypes of purple nutsedge may be important for
developing strategies for successful biological control of this weed. A
study was conducted to test for variability in susceptibility to D. higginsii
among purple nutsedge accessions from Brazil, Florida, and Hawaii. Studies
on morphological and physiological characteristics indicated the presence of
distinctive intraspecific biotypes in the Brazilian weed population. An
isolate of D. higginsii, isolated from diseased purple nutsedge plants found
in Florida, was cultured on PDA medium. A suspension of 106 conidia/ml was
used to inoculate 21-days old plants. The conidial suspension was amended
with 0.5% Metamucil. This amendment, without the fungus, was used as a
control. Plants were evaluated 15 days after inoculation for pathogenicity
based on a visual disease assessment scale (0=immune, 1 and 2=resistant, 3
and 4=susceptible). The experiment was done twice and populations that rated
0-2 were tested again to confirm their response to the pathogen. Also,
attempts were made to re-isolate the fungus from inoculated leaves. Results
indicated that among the nutsedge accessions tested, 90.5% were susceptible,
7.9% resistant and 1.6% immune. Molecular variability among accessions is
being characterized by RAPD analysis to determine the genetic make up of
purple nutsedge populations and to identify possible genetic markers of
susceptibility to D. higginsii.
USEFULNESS/APPLICATION OF THE FINDINGS: These findings enable further
development of bioherbicides for hydrilla, nutsedges, pigweeds, tropical soda
apple, waterhyacinth, and weedy grasses.
WORK PLANNED FOR NEXT YEAR: Efforts to develop bioherbicides for the
above-mentioned weeds will be continued.
Publications:
Journal Articles:
Martinez Jimenez, M., and Charudattan, R. 1998. Survey and evaluation of
Mexican native fungi for biocontrol of waterhyacinth. J. Aquat. Plant
Manage.36:145-148.
Pitelli, R.A., Charudattan, R., and DeValerio, J.T. 1998. Effect of Alternaria
cassiae, Pseudocercospora nigricans, and soybean (Glycine max) planting
density on the biological control of sicklepod (Senna obtusifolia).
Weed Technol. 12:37-40.
Smither-Kopperl, M.L., Charudattan, R., and Berger, R.D. 1998. Dispersal of
spores of Fusarium culmorum in aquatic systems. Phytopathology
88:382-388.
Smither-Kopperl, M.L., Charudattan, R., and Berger, R.D. 1999. Plectosporium
tabacinum, a pathogen of the invasive aquatic weed Hydrilla
verticillata in Florida. Plant Dis. 83:24-28.
Abstracts:
Bianco, S., Pitelli, R.A., Bellingieri, P.A, Mullahey, J.J., and Charudattan,
R. 1998. Growth and nutrient uptake by tropical soda apple (Solanum
viarum Dunal). WSSA Abstracts. 38:21.
Chandramohan, S., and Charudattan, R. 1998. A technique for mass production
and multiple-harvesting of two bioherbicide fungi by solid-substrate
culturing. WSSA Abstracts. 38:81.
Chandramohan, S. and Charudattan, R. 1998. Host-Specific Response of
Pathogens in a Mixture on Different Weed Hosts: an Electron Microscopic
Study. Phytopathology 88 (Suppl.):S15.
Chandramohan, Charudattan, R., Sonoda, R.M., and Singh, M. 1999. Field tests
of a pathogen mixture for bioherbicidal control of guineagrass (Panicum
maximum Jacq.). WSSA Abstracts 39:75.
DeValerio, J.T. and Charudattan, R. 1999. Field testing of Ralstonia
solanacearum [Smith] Yabuuchi et al. as a biocontrol agent for tropical
soda apple (Solanum viarum Dunal). WSSA Abstracts 39:70.
Elwakil, M.A., Shabana, Y.M., Charudattan, R., Baka, Z.A.M., Abdel-Fattah, G.M.
1998. Development of Alternaria eichhorniae for biological control of
waterhyacinth in Egypt. In: M.H. Belal, V. Beyssat-Arnaouty, and S.A.
El Arnaouty, Eds. Proceedings of Regional Symposium for Applied
Biological Control in Mediterranean Countries, Oct. 25-29, 1998, Cairo,
Egypt. Center of Biological Control, Faculty of Agriculture, Cairo
University, Cairo, Egypt.
Kadir, J. and Charudattan, R. 1998. Factors affecting the efficacy of
Dactylaria higginsii (Luttrell) M.B. Ellis as a bioherbicide for
control of purple nutsedge (Cyperus rotundus L.). WSSA Abstracts.
38:45.
Pereira, W., Charudattan, R., and Kadir, J. 1998. Susceptibility of purple
nutsedge (Cyperus rotundus) accessions to Dactylaria higginsii
(Lutrell) M.B. Ellis. WSSA Abstracts. 38:45.
Shabana, Y.M., Cuda, J.P., Charudattan, R. 1998. Integrated control of
Hydrilla verticillata with fungal and insect biocontrol agents.
Phytopathology 88 (Suppl.):S80.
Shabana, Y.M., Elwakil, M.A., and Charudattan, R. 1998. Status and progress
of biological control of waterhyacinth, Eichhornia crassipes, in Egypt.
Abstracts, 7th Int. Congr. Plant Pathol., Edinburgh, Scotland. Abstr.
No. 5.2.41.
Smither-Kopperl, M.L., Charudattan, R., Berger, R.D. 1998. A model system to
investigate the spread of Plectosporium tabacinum disease on hydrilla.
Phytopathology 88 (Suppl.):S83.
Tessmann, D.J. and Charudattan, R. 1998. Pathogenic variability of Cercospora
piaropi and C. piaropi on waterhyacinth (Eichhornia crassipes). WSSA
Abstracts. 38:79.
Tessmann, D.J., Charudattan, R., Kistler, H.C. 1998. A molecular
characterization of Cercospora species pathogenic to waterhyacinth
(Eichhornia crassipes) based on three conserved genes. Phytopathology
88 (Suppl.):S88.
Vincent, A.C. and Charudattan, R. 1999. Effects of formulations of
Myrothecium roridum Tode ex. Fr. and Cercospora rodmanii Conway on
waterhyacinth (Eichhornia crassipes [Mart.] Solms-Laub.) Under
greenhouse and field conditions. WSSA Abstracts 39:71.
Wyss, G.S., Henkel, T., Charudattan, R., and DeValerio, J.T. 1999.
Mass-production of conidia of Dactylaria higginsii (Luttrell) M.B.
Ellis, a potential biocontrol agent for nutsedges (Cyperus spp.)
on natural and synthetic media and grains. WSSA Abstracts 39:74.
Yandoc, C. and Charudattan, R. 1998. Use of natural substrates for the
production of fungal inoculum for biological weed control studies.
WSSA Abstracts. 38:80.
Yandoc, C.B., Chandramohan, S., Charudattan, R., and Shilling, D.G. 1998.
Evaluation of fungal isolates for their potential as biological control
agents for cogongrass [Imperata cylindrica (L.) Beauv.]. WSSA
Abstracts. 38:45.
Yandoc, C.B., Charudattan, R., and Shilling, D.G. 1999. Enhancement of
efficacy of Bipolaris sacchari (E. Butler) Shoem., a bioherbicide
agent of cogongrass [Imperata cylindrica (L.) Beauv.], with adjuvants.
WSSA Abstracts 39:72.
Book Chapters:
Charudattan, R. 1998. Experience on water hyacinth control in USA.
Pages 47-51. Anonymous eds., in: Reunion Regional Sobre Control
Integrado del Lirio Acuatico. Instituto Mexicano de Technologia del
Agua, Cuernavaca, Mexico. Nov. 24-28, 1997. Organizacion de la
Alimentacion y la Agricultura de las Naciones Unidas, FAO, Roma.
Isaccson, D.L. and Charudattan, R. 1999. Biological control of weeds.
Pages xxx-xxx In: Handbook of Pest Management, J.R. Ruberson, ed.
Marcel Dekker, New York.
Rosskopf, E.N., Charudattan, R., and Kadir, J.B. 1999. Use of Plant
Pathogens in Weed Control. Pp. 891-918, in: T.W. Fisher and T.S.
Bellows, eds. Handbook of Biological Control. Academic Press,
New York, New York. In press.
FLORIDA
Erin N. Rosskopf
USDA-ARS, USHRL, Ft. Pierce, FL 34945;
TEL: 561- 467-3081; FAX: 561-467-6062
E-mail: erosskopf@msn.com
OBJECTIVE 1: Evaluate selected pathogens as bioherbicides.
Studies were conducted through the 1998 and beginning 1999 pepper and tomato
production seasons to determine weed species that will be dominant in the
absence of methyl bromide for soil fumigation. Portulacca spp., Cyperus
spp., and Amaranthus spp., as well as several genera in the family Poaceae
were found to be most plentiful. Fungi currently under development include
Phomopsis amaranthicola for control of Amaranthus spp. and Dactylaria
higginsii for control of Cyperus spp. A cooperative project with Dr. Robert
Kohlberg and Dr. Tony Ceasar has been established to test the efficacy of P.
amaranthicola for control of pigweeds in sugar beet production areas.
Testing of D. higginsii and P. amaranthicola for pesticide compatibility is
currently underway. This work is being done cooperatively with Dr. R.
Charudattan. Two field trials testing for herbicide and fungicide tank mix
compatibility have been designed and will be established within the coming
month. Dichotomophthora portulacae and a Fusarium spp. have been isolated
from Portulacca spp. from local field sites and are under evaluation for
control of weeds in this genus. Twenty-two isolates collected from Bidens
pilosa and twelve isolates collected from Ambrosia spp. were screened for
pathogenicity to these weeds. A single isolate from Bidens pilosa showed
significant promise and has been sent to Dr. Kerry O'Donnell for
identification. None of the isolates collected from Ambrosia spp. have been
effective in causing disease under greenhouse conditions. Eighteen fungal
isolated have been obtained from a variety of grass weeds showing leaf-spot
symptoms, but these isolates have yet to be screened.
OBJECTIVE 2: Enhance the efficacy of bioherbicide candidates.
Studies have been conducted and are continuing in which efficacy of
Dactylaria higginsii inoculum produced on a variety of media is compared.
Conidia produced on eight different media were screened for viability using
36 vapor pressure deficits under 5 different temperatures. Significant
differences were found among germinability of conidia produced on different
media. It was determined that the fungus could be induced to produce
chlamydospores using high levels of glycerol as a component in the medium.
Germinability of chlamydospores produced in this manner was confirmed, but
infectivity has yet to be proven.
OBJECTIVE 3: Develop systems for mass-production of stable bioherbicide
formulations.
Studies are currently underway to establish a means of producing
Dichotomophthora portulacae inoculum. Several solid and liquid media have
been tested, including a variety of grains and sugarcane by-products. A
satisfactory method has not been established and this work continues.
OBJECTIVE 4: Develop genetic characterization and transformation of
bioherbicide candidates as a means of enhancing and assessing environmental
risk.
No work on this objective at this time.
USEFULNESS/APPLICATION OF THE FINDINGS: The cooperative efforts aimed at
developing Dactylaria higginsii and Phomopsis amaranthicola are extremely
important and useful at this time. The loss of methyl bromide as a soil
fumigant makes the availability of these fungi crucial for weed control
efforts. Control of nutsedge is of particular concern and any advances that
allow for incorporation of D. higginsii into the existing tomato and pepper
production systems are useful.
WORK PLANNED FOR NEXT YEAR: An Organization for Economic Co-Operation and
Development Fellowship was obtained in order to visit Dr. Sue Boyetchko of
the research center in Saskatoon, Saskatchewan, Canada. This trip is focused
on learning techniques to be used for developing an integrated approach for
weed management using deleterious rhizobacteria and foliar fungi.
A cooperative project will be established with Dr. Bill Connick and Dr. Don
Daigle to develop and evaluate various formulations of several potential
biological control agents.
Publications:
Rosskopf, E.N. 1998. Evaluation of Phomopsis amaranthicola sp. nov. as a
biological control agent for Amaranthus spp. Ph.D. dissertation.,
Univ. of FL, Gainesville, FL. 190 pp.
Rosskopf, E.N., Charudattan, R., and Kadir, J.B. 1999. Use of Plant
Pathogens in Weed Control. Pp. 891-918, in: T.W. Fisher and T.S.
Bellows, eds. Handbook of Biological Control. Academic Press,
New York, New York. In press.
ILLINOIS
M.A. Jackson, D.A. Schisler and R.J. Bothast
Fermentation Biochemistry Research Unit, National Center for Agricultural
Utilization Research USDA-ARS 1815 N. University St. Pioria, IL 61604
TEL: 309-681-6567; FAX: 309-681-6427
E-mail: JACKSOMA@MAIL.NCAUR.USDA.GOV;SCHISLDA@MAIL.NCAUR.USDA.GOV
RBOTHAST@NCAUR.USDA.GOV
Objective 3: Develop systems for mass production of stable bioherbicide
formulations.
In collaboration with Dr. Keith Howard, Morehouse College, experiments were
initiated to evaluate the persistence and efficacy of COLTRU microsclerotia
incorporated in soil and stored under various soil conditions. In addition,
we have continued studies directed at reducing fermentation times for the
production of microsclerotia, Using our best production method, the
fermentation time was reduced from10 days to 6 days.
USEFULNESS/ APPLICATIONS OF FINDINGS: The results of this work provide
information on the commercial potential of COLTRU for the control of the weed
hemp sesbania.
WORK PLANNED FOR NEXT YEAR: It is anticipated that work will continue on
improving the liquid culture production method for microsclerotia of
Colletotrichum truncatum. Efforts will be made to optimize environmental
conditions (aeration, pH, temperature) in deep-tank fermentations for the
rapid production on high concentrations of microsclerotia. In addition,
studies will continue on evaluating the persistence of COLTRU microsclerotia
stored in soil under various soil conditions.
Publications:
Daigle, D.J., Connick, W.J., Jr., Boyette, C.D., Jackson, M.A., and Dorner,
J.W. 1998. Solid-state fermentation plus extrusion to make
biopesticide granules. Biotechnol. Tech. 12:715-719.
Jackson, M.A., J.S. Frymier, B.J. Wilkinson, P. Zorner and S. Evans. 1998.
Growth Requirements for the Production of Stable Cells of the
Bioherbicidal Bacterium Xanthomonas campestris. J. Ind. Microbiol.
21:237-241.
Jackson, M.A., D.A. Schisler, C.D. Boyette, W.J. Connick, Jr. and N.K. Zidack.
1998. Improving Mycoherbicide Fitness using Nutrition Management
during Production and Formulation. British Mycological Society
Symposium "The Future of Fungi in the Control of Pests, Weeds and
Diseases", Southampton, United Kingdom. P.37.
LOUISIANA
Donald J. Daigle and William J. Connick, Jr.
Southern Regional Research Center, ARS, USDA, 1100 R.E. Lee Blvd. N.O.,
LA 70124
TEL: 504-286-4527; FAX: 504-286-4419
e-mail: ddaigle@nola.srrc.usda.gov and wconnick@nola.srrc.usda.gov
OBJECTIVE 3: Develop systems for mass-production of stable bioherbicide
formulations.
Water-dispersible granule (WDG) formulations were prepared that contained
several mycoherbicide agents in collaborative research with ARS scientists in
Stoneville, MS, and at Beltsville, MD. WDGs offer the advantages of a
stable, sprayable product that can be easily measured and poured. The dew
period hurdle was addressed with the use of adjuvants such as oils, but
better technology is still needed. Growth chamber and greenhouse tests are
in progress. A 20-lb batch of Pesta granules containing an Alternaria
pathogen of dodder was prepared for field testing in 1999 (Dodder Project).
The Saskatoon Research Centre was visited for discussions about cooperative
research results and for planning of future bioherbicide research.
USEFULNESS/APPLICATION OF THE FINDINGS: If WDG formulations can be combined
with effective adjuvants for overcoming the dew period hurdle for
foliar-applied weed pathogens, commercial mycoherbicides may result.
Successful preemergence application of a dodder pathogen in Pesta may lead to
a commercial product.
WORK PLANNED FOR NEXT YEAR: Cooperative research in progress will be
continued. New regional research with Dr. Erin Rosskopf, ARS, Ft. Pierce,
FL, will begin. WDG formulations and adjuvants will be studied in an effort
to reduce the dew period hurdle. Pesta granular formulations of deleterious
rhizobacteria and various mycoherbicide agents will be prepared and
evaluated.
Publications:
Bailey, B.A., Hebbar, K.P., Strem, M.D., Darlington, L.C., Connick, W.J., Jr.,
Daigle, D.J. and Lumsden, R.D. 1998. Formulations of Fusarium
oxysporum f. sp. erythroxyli for biocontrol of Erythroxylum coca var.
coca. Weed Sci. 46:682-689.
Connick, W.J., Jr., Daigle, D.J., Pepperman, A.B., Hebbar, K.P. Lumsden, R.D.,
Anderson, T.W. and Sands, D.C. 1998. Preparation of stable, granular
formulations containing Fusarium oxysporum pathogenic to narcotic
plants. Biol. Control. 13:79-84.
Daigle, D.J., Connick, W.J., Jr., Boyette, C.D., Jackson, M.A., and Dorner,
J.W. 1998. Solid-state fermentation plus extrusion to make
biopesticide granules. Biotechnol. Tech. 12:715-719.
Daigle, D.J. and Lumsden, R.D. 1998. Formulations of Fusarium oxysporum f. sp.
erythroxyli for biocontrol of Erythroxylum coca var. coca. Weed Sci.
46:682-689.
Fravel, D.R., Connick, W.J., Jr. and Lewis, J.R. 1998. Formulation of
microorganisms to control plant diseases, in Formulation of Microbial
Biopesticides, Beneficial Microorganisms, Nematodes and Seed
Treatments (Burges, H.D., Ed.), Chapman and Hall, London, pp. 187-202.
McGuire, M.R., Connick, W.J., Jr., and Quimby, P.C., Jr. 1998. Formulation
of microbial pesticides, in Controlled Release Pesticides (Scher, H.B.,
Ed.), Marcel Dekker, New York. Accepted 6/27/97.
Yang, S-M, Dowler, W.M., Schaad, N.W. and Connick, W.J., JR. 1998. Combined
carrier and weakly virulent or non-virulent plant pathogens to control
weeds. U.S. Patent No. 5,795,845
MARYLAND
N.W. Schaad and F. Dane
USDA ARS FDWSRU Fort Detrick Bldg 1301 Foreign Pathogen-Weed Biocontrol
Frederick, MD 21702-5023
TEL: 301-619-7344; FAX: 301-619-2880
E-Mail: schaad@ncifcrf.gov
OBJECTIVE 4: A prerequisite for the release of any pathogen, regardless of
origin, is a reliable and sensitive method for it's absolute identification
from other strains. Several techniques are available including, lac ZY gene
of E. coli, moc gene of Pseudomonas fluorescens, green fluorescent protein
and lux genes. The latter has worked well for tracking Xanthomonas campestris
pv. campestris, causal agent of black rot of crucifers, over several years in
the field environment. Transgenic incorporation of lux CDABE from Vibrio
fisheri into these phytopathogenic bacteria allowed accurate detection of
bacteria in environmental samples using a CCD camera or through
bioluminescent measurements of broth enrichment cultures. Colonization of
plants with bioluminescent bacteria fluctuated with environmental conditions
and persistence was coupled to the host's growing season. Dispersal to
alternate hosts, such as weeds was detectable, while movement and persistence
in the rhizosphere was limited. Recently, a PCR-based identification system
has been developed that utilizes a 0.52-kb fatty acid desaturase (DES)
fragment derived from the unique tox-argK gene cluster of P. syringae pv.
phaseolicola as a PCR tag for Xanthomonas strains. A plasmid-borne pigG::DES
fusion was constructed and used to create chromosomal pigG mutants in several
Xanthomonas strains that are unable to make the yellow pigment
xanthomonadin. Results show that the DES tagged strain is stable and easily
identified by PCR.
Publications:
Berner, D. K., N.W. Schaad, and B. Volksch. Selection of ethlene-producing
bacteria for stimulation of Striga spp. seed germination. Biological
Control. 1999. In Press.
MISSISSIPPI
C. D. Boyette,H. K. Abbas, and R. E. Hoagland
USDA ARS, P.O. Box 350, Southern Weed Science Lab, Stoneville, MS 38776
TEL: (601)686-5217; FAX: (601)686-5222
E-Mail: dboyette@ag.gov
OBJECTIVE 1: Evaluate selected pathogens as bioherbicides.
Field tests continued to evaluate the pathogen Colletotrichum truncatum
(COLTRU) for hemp sesbania control in soybean and rice. Tests were
established in narrow-row (18" centers) soybean plots at the SWSRU
Experimental Farm. Treaments included unrefined corn oil and Silwet L-77
carriers, as well as an invert formulation. We found that hemp sesbania is
highly competitive in narrow row plots, as compared to other weeds such as
sicklepod and coffee senna. Over 90% control was achieved with both the
unrefined corn oil and invert emulsion treatments. Sicklepod and coffee
senna were seeded in narrow row soybean test plots and treated with
Colletotrichum gloeosporioides formulated with unrefined corn oil and Silwet
L-77 formulations. Both weeds were effectively controlled 10 days after
fungal applications (88 and 90%, respectively). However, weeds in untreated
plots were not competitive with soybean growth in the dense canopy.
Greenhouse and field tests were conducted to evaluate several pathogens as
bioherbicides for kudzu control. We discovered that isolates of Myrothecium
verucarria and Fusarium solani formulated with 0.2% Silwet L-77 are highly
efficacious in controlling this noxious exotic invasive weed. In
naturally-infested kudzu sites, kudzu was controlled over 90% in two
different sites.
Greenhouse and field tests revealed that M. verucarria would effectively
control spurge and purslane spp. weed complexes in tomato test plots; these
weeds are currently controlled by methyl bromide. Tomato was unaffected
either by transplanting into test plots where weeds were killed by the fungus
or by post- emergence spray treatments. We discovered that M. verucarria is
highly pathogenic to cotton. However, field tests showed that it may be
useful in late season as a biological defoliant for cotton. Applications of
M. verucarria were as effective as commercial products in replicated field
trials.
Common and multiple-seeded cocklebur was effectively controlled (85-90%) in
field test plots with applications of Alternaria helianthi formulated in
unrefined corn oil and Silwet L-77. It was discovered that the production of
an adhesive substance in A. helianthi is temperature dependent.
The natural products helvolic acid (from Aspergillus fumigatus) and a related
steroidal compound fusidic acid (from Fusidium coccineum) were found to be
highly phytotoxic against several weed spp., such as ragweeds, hemp sesbania,
sicklepod, and johnsongrass. The synthetic antibiotic trimethoprim was also
shown to be highly phytotoxic to these weed spp. The steroidal compounds
tomatine and tomatidine were found to be phytotoxic to hemp sesbania and
sicklepod, and this compound may affect host resistance to some weed
pathogens such as A. cassia, A. crassa, and A. helianthi.
USEFULNESS/APPLICATION OF FINDINGS: Narrow row and ultra-narrow row planting
of soybean and cotton is gaining popularity in the mid-South. Dense and
rapid canopy enclosures restrict the growth of some weeds, such as sicklepod,
but others, such as hemp sesbania, are relatively unaffected. The use of
bioherbicides such as COLTRU may offer opportunities for niche control
measures in these situations. In addition, the dense and rapid canopy
enclosures promote weed disease development as found in our experiments.
The use of biological agents for controlling non-agronomic weeds such as
kudzu represents opportunities to expand the science. In addition, as shown
in our research in tomato test plots, bioherbicides offer highly effective
alternatives to environmentally hazardous chemicals such as methyl bromide.
Novel usage of nonselective bioherbicidal fungi may result in new
biologically-based agricultural products, such as biodefoliants for use in
cotton, or burn down of green growth in soybean as harvest aids.
WORK PLANNED FOR NEXT YEAR: We will continue to evaluate COLTRU for control
of hemp sesbania in narrow row cropping. We will further evaluate M.
verucarria and F. solani formulations for controlling kudzu, as well as
morningglories, redvine, spruges, purslanes, and other weeds in experimental
and naturally-infested sites, and conduct experiments to determine presence
of toxic metabolites as well as host range experiments on arboreus plants.
Field experiments will be expanded to further evaluate M. verucarria as a
biodefoliant and harvest aid in cotton and soybean. Field tests will be
conducted in soybean and cotton to further evaluate pre-and postemergence A.
helianthi formulations for control of common cocklebur.
Publications:
Abbas, H.K., and Paul, R.N. 1998. Ultrastructural effects of AAL-toxin from
the fungus Alternaria alternata on black nightshade (Solanum nigrum)
leaf discs and correlation with biochemical measures of phytotoxixcity.
Toxicon 36:1821-1832.
Daigle, D.J., Connick, W.J., Jr., Boyette, C.D., Jackson, M.A., and Dorner,
J.W. 1998. Solid-state fermentation plus extrusion to make
biopesticide granules. Biotechnol. Tech. 12:715-719.
Quimby, P.C., Jr., Zidak, N., Boyette, C.D., and Grey, W. P. A method for
stabilizing and granulating Microbial biological control agents.
Biocontrol Sci. and Tech. (In press).