Volume 5 Special Issue 1 2011
How to reference: Evidente A, Andolfi A, Cimmino A (2011) Fungal Phytotoxins for Control of Cirsium arvense and Sonchus arvensis. In: Peng G, Wolf TM (Eds) Bioherbicides. Pest Technology 5 (Special Issue 1), 1-17
Gary Peng, Thomas M. Wolf
Agriculture and Agri-Food Canada, Saskatoon Research Centre, Canada
CONTENTS AND ABSTRACTS
Antonio Evidente, Anna Andolfi, Alessio Cimmino (Italy) Fungal Phytotoxins for Control of Cirsium arvense and Sonchus arvensis (pp 1-17)
Invited Review: Perennial weeds, including Cirsium arvense and Sonchus arvensis, are a common problem in crop fields, especially in agricultural systems with reduced herbicide usage. Herbicides recommended for control of these perennials generally are restricted to only a few active ingredients that tend to have low selectivity, especially on dicot crops. Microbial phytotoxins or their synthetic analogues may be candidates for new weed-control options. Many plant pathogens, especially necrotrophic or hemibiotrophic fungi, produce a range of phytotoxins responsible for disease damage and may be a source of such useful metabolites. Several pathogens, including Stagonospora cirsii and Ascochyta sonchi, were found commonly on C. arvense and S. arvensis, and these fungi also produce phytotoxic metabolites. Phyllosticta cirsii and Phomopsis cirsii, belonging to two well-known toxin-producing genera, have also been proposed for biocontrol of C. arvense. Phytotoxins isolated from these fungal pathogens are metabolites belonging to several classes of natural compounds including enol pyruvic acid derivatives, cytochalasins, nonenolides, oxazatricycloalkenones, pentasubstituted bicyclooctatrienyl ester of acetic acid, pentasubstituted hexahydrobenzodioxine carboxylic acid methyl ester, and β-nitropropionic acid. Some of these metabolites may be used as biomarkers, for studies on mode of action and development of structure-activity relationships.
Gary Peng, Thomas M. Wolf (Canada) Synergy between Synthetic and Microbial Herbicides for Weed Control (pp 18-27)
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Invited Mini-Review: Synthetic herbicides have been investigated as tools to synergize mycoherbicides (fungal bioherbicides) for improved efficacy or management of hard-to-control weed problems. Herbicides may weaken weeds and impair their defence systems, thus making weeds more vulnerable to mycoherbicide infection. Despite many positive results, the practical value of synergy remains elusive. This review will discuss several fundamental aspects of synergy relating to development of this technology based on author’s own experiences in biocontrol of green foxtail and scentless chamomile. These include application timing, dose effect, weed growth stage, and spray retention efficiency. Issues relating to the practicality, non-target risks, and cost of weed control are stumbling blocks to the adoption of synergistic technologies, and some tactics are proposed to address these challenges.
A. J. Caesar (USA) The Importance of Intertrophic Interactions in Biological Weed Control (pp 28-33)
Invited Mini-Review: The earliest research leading to successful weed biocontrol included observations and some analysis that the strict “gate-keeping” by peer reviewers, editors and publishers does not often allow today. Within these pioneering studies was a valid picture of the biology of weed biocontrol that is applicable today. Two major studies pointed to successful weed biocontrol of perennials as an outcome of intertrophic interactions. Later work indicated that there was a consistent association of certain fungal species with insect damage. In recent years, ecological studies have provided evidence of the effect of the soil microbiota in combination with root herbivory on plant community structure and on invasiveness. This accretion of evidence and the authors own findings have led to the conclusion that in selecting agents for biocontrol of exotic perennial invasive plants, the capacity of the agent to synergistically interact with other agents should be included in the criteria. If the hypothesis that insect/pathogen interactions underlie successful biocontrol of herbaceous perennial invasive plant species, then efforts to restore native plants would be affected by the biotic legacy of the interactions. Findings from a post-biocontrol native plant restoration have provided such evidence. The existence of insect/pathogen interactions provides a unique position for plant pathogens as being an important factor prior to, during and after biocontrol.
Graeme W. Bourdôt, David J. Saville (New Zealand), Meindert D. de Jong (The Netherlands) Evaluating the Environmental Safety of Broad-host-range Bioherbicides (pp 34-40)
Invited Mini-Review: Broad-host-range pathogens, indigenous in their areas of intended use as bioherbicides and endemic in populations of the weeds of interest, are more appealing commercially than host-specific pathogens because of their wider market potential. However, these pathogens may spread in space and/or in time following their application, thereby potentially increasing the risk of disease to non-target host plants. The ratio of the density of inoculum added to the non-target host plant’s environment by the bioherbicide to that occurring naturally, can be used to assess the ‘relative risk’ of the bioherbicide and determine its acceptability and/or best management practice. Empirical and modelling methodologies have been used for quantifying the additional and natural background inoculum levels of an indigenous plant pathogen being considered for development as a bioherbicide, enabling the ratio of ‘added to natural’ inoculum density to be determined. We first review how this ratio has been used to define a minimum isolation distance, or safety zone, between areas of application and locations of non-target host plants, using the example of Sclerotinia sclerotiorum applied to Cirsium arvense in permanent pasture in New Zealand. Secondly, we consider how the ratio has been applied for the same purpose but at a much larger geographic scale using as examples Chondrostereum purpureum deployed for weed control in forests in the Netherlands and on Vancouver Island. Lastly we review how the ratio has been used to determine the duration of a withholding period using, again, the S. sclerotiorum - C. arvense system. Determining an acceptable value for the ratio requires knowledge of the relationship between the disease that a bioherbicide pathogen causes in non-target host plant populations, and the pathogen’s inoculum density.
Gavin J. Ash (Australia) Biological Control of Weeds with Mycoherbicides in the Age of Genomics (pp 41-47)
Invited Mini-Review: Mycoherbicides offer an innovative approach to the management of weeds in disturbed environments using formulated fungal phytopathogens. The efficacy of these mycoherbicides could be improved in the future through the application of genomics (the study of genes and their interactions) to both the target and the biological control agent. In this review, an update is given on approaches to genetic enhancements of mycoherbicides and how a knowledge of, and recent advances in, genomics could be used to improve this process. Specific examples are given of novel approaches that could be used. Genetic modification of mycoherbicidal agents has been shown to be possible, but caution is warranted in terms of public perception and the acceptance of these approaches in the wider community.
John Lydon, Hyesuk Kong, Charles Murphy (USA), Wenming Zhang (Canada) The Biology and Biological Activity of Pseudomonas syringae pv. tagetis (pp 48-55)
Invited Review: Pseudomonas syringae pv. tagetis (Pst) is a disease of plants in the family Asteraceae. A distinctive characteristic of this bacterial pathogen is the symptom of apical chlorosis in infected plants, caused by the phytotoxin tagetitoxin. Strains of Pst have been isolated from several plant species from a number of countries. One strain isolated from Cirsium arvense (Canada thistle) has been evaluated as a biological control agent for this invasive weed and other weeds in the family Asteraceae. Genetic analysis of the strains in this pathovar indicate that it is highly clonal. There is another strain of P. syringae (CT99) that was also isolated from Canada thistle and causes apical chlorosis that may produce tagetitoxin as well. However, multilocus sequence typing analysis indicates that it is not a Pst strain. The major impact of Pst on infected plants is stunting and the reduction in sexual reproductive structures, symptoms attributed to tagetitoxin. While initially considered for the control of Canada thistle, the utility of this pathogen as a biological control agent may be limited to controlling annual weeds. Alternatively, tagetitoxin may be of value as a natural herbicide because of its impact on chloroplasts.
Jianping Zhang, Shuang Yang, Yongjun Zhou, Liuqing Yu (China) Development of Bioherbicides for Control of Barnyard Grass in China (pp 56-60)
Invited Mini-Review: Research progress on bioherbicides against barnyard grass in rice fields was reviewed with a focus on Chinese perspective. In China, barnyard grass is one of the most problematic weeds in paddy rice fields. Several fungal biocontrol agents have been studied extensively and the most promising candidates explored for commercial development, including strain selection and improvement, inoculum mass production, formulation, efficacy trials under various conditions, synergy with chemical herbicides, and safety to crops. Overall, mass production and formulation technologies have proved to be the major stumbling blocks that hinder bioherbicide development. Strategies are discussed to overcome the challenges and facilitate the development of selected fungal agents into commercial bioherbicide products.
Yunzhi Zhu, Sheng Qiang (China) Curvularia eragrostidis, a Promising Mycoherbicide Agent for Grass Weeds (pp 61-66)
Invited Mini-Review: A fungal pathogen isolated from diseased leaves of large crabgrass (Digitaria sanguinalis) at three different geographic locations in China was identified as Curvularia eragrostidis. A series of biological assessments have been carried out to determine the potential of the fungus as a bioherbicide agent. The fungus is able to germinate and grow in a very wide range of temperature (10-40ºC) or pH (2-11) conditions, although 28°C and pH 6 were optimal. This implies a great versatility for infection of weeds under field conditions. Several phytotoxins have been identified from C. eragrostidis cultures. At least two of them, α,β-dehydrocurvularin and helminthosporin, are associated with the pathogenicity on crabgrass. The α,β-dehydrocurvularin impairs the PS-II reaction center and inhibits re-oxidation of the primary electron acceptor (QA) of photosynthesis. With slightly different modes of action, the helminthosporin affects the chloroplast function of large crabgrass leaves. Forty-one plant species belonging to 20 families were inoculated with C. eragrostidis to assess a potential host range. Many of these were important crop species commonly grown in China, including rice, corn, soybean, cotton, and peanut. The fungus caused no disease or any other negative impact on the crop species tested, while resulted in infection on several additional grass weeds including Chinese crabgrass and Chinese sprangletop. This reveals a potential broader spectrum of weed control. Formulation is urgently needed to make this bioherbicide agent perform consistently under field conditions.
Thomas M. Wolf, Gary Peng (Canada) Improving Spray Deposition on Vertical Structures: The Role of Nozzle Angle, Boom Height, Travel Speed, and Spray Quality (pp 67-72)
Original Research Paper: In order to be effective, bioherbicides need to be deposited on the most susceptible weed plant tissues. For bioherbicides that attack above-ground vegetation, vertically oriented vegetative structures such erect leaves, stems or petioles typically receive much lower dosages compared to horizontally-oriented targets. Experiments were conducted to study the effects of travel speed, nozzle configuration, boom height and spray quality on spray deposition on simulated vertically-oriented surfaces. Results showed that a combination of forward-angled nozzles, coarser sprays, lower boom height, and faster travel speed increased spray retention on these vertical targets by more than 100%. These results indicate that optimization of application parameters potentially contribute to better performance of those bioherbicides whose efficacy depends on sufficient spray deposition and infection on vertical surfaces of the target.
Karen L. Bailey (Canada), Stuart Falk (USA) Turning Research on Microbial Bioherbicides into Commercial Products ─ A Phoma Story (pp 73-79)
Original Research Paper: The literature cites many claims of potential new bioherbicides based on isolate screening and biological assessment. However, only 8.1% have achieved verifiable commercial success, 19.4% uncertain (i.e. registered but not commercialized), and 72.5% have been ineffective. To get more bioherbicides to the marketplace there must be a better partnership between business and science in order to strengthen the research supporting commercialization. This paper describes how a bioherbicide innovation chain (research model) has been merged with the stage and gate process (business model) to develop Phoma macrostoma for broadleaved weed control. Prior to industry involvement, research concentrated on discovery and proof-of-concept by characterizing the fungus, evaluating fermentation requirements, demonstrating efficacy and environmental safety, learning the mode of action, and studying the economics and market potential. The inclusion of industry to assist with technology assessment and product development brought new perspectives and defined key decision points that would either let the project proceed or stop it completely. Key issues were: economically feasible fermentation process; consistent and high efficacy; long shelf life stability; safety to mammals and the environment. Presently, P. macrostoma is in the latter stages of pre-commercialization completing the pilot scale manufacturing process and waiting for the regulatory decisions in anticipation of a product launch.
Russell K. Hynes, Susan M. Boyetchko (Canada) Improvements to the Pesta Formulation to Promote Survival and Dispersal of Pseudomonas fluorescens BRG100, Green Foxtail Bioherbicide (pp 80-87)
Original Research Paper: A modified pesta granule was developed for Pseudomonas fluorescens BRG100, a bioherbicidal bacterium for grass weeds, green foxtail (Setaria viridis) and wild oat (Avena fatua). This study reports: i) the effect of formulation water activity (aw) on survival of P. fluorescens BRG100 and, ii) the effect of starch on disintegration and dispersal of a green fluorescent protein transformant of P. fluorescens BRG100 from pesta in laboratory sand columns. The long-term refrigerated storage stability of P. fluorescens BRG100 was examined in pesta granules dried to different aw. Drying pesta to 0.3 aw stabilized the population of P. fluorescens BRG100 for 16 months at 8.5 log10 cfu/g. When pesta was dried to 0.8 aw, P. fluorescens BRG100 population decreased to 7.3 log10 cfu/g over six months. The impact of starch addition (corn, pea, rice and potato) to pesta and concentration (13% and 26%, wt/wt) on the disintegration rate of pesta granules was determined with laser diffractometry. The order of fast to slow disintegration following starch amendment was pea>potato>corn> rice. Increasing pea, potato and corn starch content from 13 to 26% promoted faster disintegration of pesta, conversely, increasing rice starch content decreased disintegration. Half-life disintegration profiles were determined with pea starch amended pesta (26% w/w) being most rapid, 0.8 minute, rice starch (26% w/w) amended pesta was slowest, 4 minutes and non-amended pesta, 2.5 minutes. P. fluorescens BRG100gfp was detected 2 hr earlier in the middle and bottom sections of the sand columns from corn starch amended (26%) pesta than from non-amended pesta. The ability to produce pesta granules with different disintegration and bioherbicide release characteristics provides the formulator with the potential to design pesta that insures the active ingredient is delivered to the pest when it is most susceptible.
Robert E. Hoagland, Clyde D. Boyette, Kevin C. Vaughn (USA) Interactions of Quinclorac with a Bioherbicidal Strain of Myrothecium verrucaria (pp 88-96)
Original Research Paper: The fungus, Myrothecium verrucaria (Alb. & Schwein.) (IMI Accession No. 3601690) (MV), is being developed as a bioherbicide for kudzu [Pueraria lobata (Willd.) Ohwi] and other invasive weeds. Spore and mycelial formulations of MV exhibit relatively rapid bioherbicidal activity when applied to the foliage of these weeds, and that application of MV with the herbicide glyphosate [N-(phosphonomethyl)glycine] can exhibit synergistic herbicidal interactions in certain instances. Several synthetic auxin-type herbicides are labeled for use to control kudzu. The auxin-type herbicide quinclorac (3,7-dichloro-8-quinolinecarboxylic acid) is not labeled for kudzu control, but is effective on hemp sesbania [Sesbania exaltata (Raf.) Rybd. Ex. Hill]. In bioassays of hemp sesbania and sicklepod (Senna obtusifolia L.) seedlings and in greenhouse tests using kudzu plants, sub-lethal concentrations of both MV and quinclorac (high purity, technical grade) applied to plant tissues caused some additive and/or synergistic effects on the reduction of growth and chlorophyll accumulation. These important findings under controlled conditions provide the basis for further characterization of MV and quinclorac interactions on weeds under field conditions.
Clyde D. Boyette, Charles T. Bryson, Robert E. Hoagland (USA) Biological Control of Cucurbita pepo var. texana (Texas Gourd) in Cotton (Gossypium hirsutum) with the Fungus Fusarium solani f. sp. cucurbitae (pp 97-101)
Original Research Paper: Experiments were conducted to evaluate various formulations and application methods of the fungus Fusarium solani f. sp. cucurbitae (FSC)for controlling Texas gourd (Cucurbita pepo var. texana) in cotton. In greenhouse tests, Texas gourd was controlled 93% and 96%, respectively, with pre-emergence applications of FSC-infested cornmeal/sand medium (CMS) and FSC-wheat flour/kaolin (‘Pesta’) granules. Post-emergence applications of CMS or ‘Pesta’ granular formulations were less effective overall. However, >90% control of Texas gourd was achieved with post-emergence applications of FSC spores formulated in an emulsion consisting of 25% unrefined corn oil and 0.2% Silwet L-77 surfactant. Dew was not required to achieve optimal levels of weed control with either the pre-emergence granular formulations or with post-emergence corn oil/surfactant applications. In field tests, pre-emergence applications of FSC-infested CMS and FSC-‘Pesta’ granules controlled 90-94% of the weeds. Post-emergence applications of FSC formulated in corn oil/surfactant were equally efficacious in controlling Texas gourd in cotton. No damage to cotton was observed.
James T. DeValerio, R. Charudattan, J. Jeffrey Mullahey, Pamela D. Roberts (USA) Application of a Bacterial Pathogen, Ralstonia solanacearum, with a Wet-blade Mower for Biological Control of Tropical Soda Apple, Solanum viarum (pp 102-107)
Research Note: Tropical soda apple (Solanum viarum Dunal; TSA) is an invasive noxious weed in Florida and several southeastern U.S. states. To develop a bioherbicide agent that could be integrated with mowing, a recommended management practice for TSA, we screened several isolates of bacterial pathogens of Solanaceous plants and established that a Ralstonia solanacearum (=Pseudomonas solanacearum) (RS) isolate (10 Q, Race 1), originally from tomato, was capable of killing TSA without affecting tomato. RS is a xylem-invading, wilt-causing pathogen that when applied to cut main stems of TSA prevented regrowth and killed TSA plants under greenhouse conditions. To determine the effectiveness of this model bacterial bioherbicide agent under field conditions, a novel application method using a wet-blade mower was tested. Whereas wet-blade systems are used to deliver chemical herbicides and plant growth regulators to target weeds while mowing, none has been tested to deliver a biocontrol agent. We used the Burch Wet BladeTM mower system (BWB) and conducted the study in a pasture with 18% TSA coverage. RS cells suspended in sterile tap water at 1.4 x 109 CFU units/ml were used as inoculum. Treatments included a BWB-applied control (culture medium without RS), RS applied at 23 L/ha with BWB, and RS applied at 23 L/ha with BWB plus RS over-sprayed at 560 L/ha with a backpack sprayer. Both RS treatments reduced TSA regrowth compared to the control (P = 0.0003). There was no difference between the wet-blade-applied RS treatment and the wet-blade + over-sprayed RS treatment. The wet-blade mower was an effective, practical means of application of the bacterial wilt pathogen to control TSA and it may have broader applicability to other types of wilt-causing pathogens.