LAB93934 - Biology Control and Risk Management of Soybean Diseases in Louisiana

Robert Carver, Schneider, Raymond W.

START: 01 OCT 2008 TERM: 30 SEP 2013 FY: 2010

INVESTIGATOR: Schneider, R. W.



KA Subject Science Pct
202 1820 1080 10
212 1820 1160 30
215 1820 1102 20
216 1820 1160 40

CLASSIFICATION HEADINGS: R202 . Plant Genetic Resources; S1820 . Soybean; F1080 . Genetics; R212 . Pathogens and Nematodes Affecting Plants; F1160 . Pathology; R215 . Biological Control of Pests Affecting Plants; F1102 . Mycology; R216 . Integrated Pest Management Systems


NON-TECHNICAL SUMMARY: Louisiana is a haven for diseases of soybean. Diseases that are considered to be minor in other states may be yield-limiting in Louisiana and other Mid-Gulf states. Therefore, we must develop disease management and control strategies and tactics that may not be practiced elsewhere. This requires that we discover the basic knowledge regarding disease cycles and attempt to identify those aspects of the various disease cycles that are subject to manipulation. This may include altered fertility practices, fungicide applications at specific growth stages, selection for disease-resistant varieties, use of certain maturity groups to escape diseases and other practices. For example, we found that the addition of chloride in form of muriate of potash greatly reduces severity of Asian soybean rust and Cercospora leaf blight. Another example is our finding that spore production by the rust pathogen is virtually arrested at temperatures above 92 degrees F. Thus, we can alter our planting schedule and maturity groups so that plants are at their most susceptible stage during the warmest months. In addition, we must learn about the pathogens. What is their propensity for genetic shifts leading to more virulent strains? Under what conditions do they reproduce? How far do spores spread? What other topics may lead to new disease management tactics? Such studies may be conducted in growth chambers using detached leaves where environmental conditions can be precisely controlled, and the findings would then be verified with field experimentation. Genetic assessments of populations of pathogens would use molecular techniques such as DNA fingerprints to assess large collections of pathogens over several years from diverse locations. This would enable us to identify newly emerging strains that may supersede current strains and render current soybean varieties more susceptible. All of these studies are overlaid with economic considerations. For example, if a certain fungicide is identified as effective in disease control but its application would cost more than the economic returns to be gained by the producer, then this disease-control tactic would not be recommended. Addressing these very complex issues requires several years of field experimentation and validation. Outcomes and Impacts Change in knowledge: New knowledge will be discovered during the course of these investigations with regard to soybean diseases and the development of disease management and control practices for these diseases. Change in actions: It is anticipated that new disease-control and management technologies will be discovered, tested and documented during the course of these investigations. These will result in new recommendations for soybean producers in the area of pest management.

OBJECTIVES: 1. To assess damage caused by common soybean diseases. 2. To develop disease-severity and yield-loss forecasting models for selected soybean diseases and to develop cost:benefit models for use in disease management decision aids. 3. To develop management and control strategies for soybean diseases. 4. To elucidate certain aspects of disease cycles that will aid in developing disease-control strategies and tactics. 5. To identify certain environmental factors that either repress or enhance development of selected soybean diseases and to develop risk-assessment strategies and tactics related to disease management.

APPROACH: For yield-loss studies, the basic approach is to include two treatments in which the disease of interest is controlled in one treatment with appropriate fungicides and the disease is allowed to develop in the other treatment; yields are then compared. However, in practice there are complications. Specific soybeans varieties are susceptible to multiple diseases. Ratings for all diseases are then made on a regular basis throughout the season in the no-fungicide treatment, and yields are compared for all varieties between the fungicide-treated and nontreated treatments. Knowing that varieties differ in their susceptibility to each of the diseases, the effects of each disease can then be discerned by the use of disease progress curves for each disease, multiple regression analysis and other statistical and modeling techniques. The best means for controlling diseases is the use of resistant varieties. Towards this end, varieties will be evaluated for disease reactions. Also, we will continually screen fungicides for efficacy in controlling diseases in statewide field trials. More detailed information, e.g. rates and times of application, particularly with new compounds, will be developed in replicated field experiments. Other means of disease management and control include time of planting, row spacing, crop rotation and altered mineral nutrition regimens. Such practices will be evaluated in replicated field trials in cooperation with other extension and research faculty. These are long-term projects that can be easily integrated into agronomic rotation studies conducted at research stations. One of the more promising means of cultural disease control is the use of prescription mineral nutrition supplements. We succeeded in documenting that severities of ASR and Cercospora leaf blight were reduced with supplemental chloride nutrition. Chloride was added in the form of muriate of potash. Tissue analyses clearly indicated that the response was to chloride rather than potassium. These intriguing results must be pursued, and after we establish specific tissue concentrations associated with disease suppression, we will conduct physiological studies to elucidate the mode of action. Knowledge of disease cycles often leads to disease-management strategies. The lack of knowledge regarding overwintering survival of C. kikuchii is surprising. For example, we do not know if this pathogen can survive on soybean debris or if it has alternative hosts that serve as inoculum reservoirs. It would probably be useful to assess other crop species as hosts for this and other pathogens in order to reduce inoculum loads from year to year. Certain molecular markers now allow us to assess genetic relationships without having to conduct pathogenicity tests. Of course, such tests will be conducted to verify the identity of likely isolates. Furthermore, we know very little about alternative hosts for such pathogens as Diaporthe and Phomopsis and the anthracnose pathogen.

KEYWORDS: soybean; soybean diseases; disease control; cultural control; disease resistance; risk models; yield loss models; fungicides; population genetics

PROGRESS: 2010/01 TO 2010/12
OUTPUTS: The fungus Simplicillium lanosoniveum, which we first identified as a mycoparasite of Phakopsora pachyrhizi, was effective as a biological control agent as determined in extensive field experimentation. A patent disclosure was filed for eventual intellectual property protection, and a biotechnology company expressed interest in commercializing this organism. This project resulted in four published abstracts, five published proceedings, and 11 presentations in 2010. PARTICIPANTS: Nothing significant to report during this reporting period. TARGET AUDIENCES: Nothing significant to report during this reporting period. PROJECT MODIFICATIONS: Nothing significant to report during this reporting period.

IMPACT: 2010/01 TO 2010/12
1. Documentation of the extended latent period with the Cercospora leaf blight pathogen is the first report of this unique phenomenon. The practical implication is that fungicide efficacy is greatly impacted by when the fungicide is applied relative to time of infection. Current dogma dictates that fungicides should be applied during mid-reproductive growth; however, this is probably too late for a single or double application to provide season-long control. In fact, we demonstrated that when any of several materials is applied before the onset of latent infection along with a second application during reproductive stages of plant development, this disease is manageable, whereas it has been recalcitrant until now. We documented 22% yield loss attributable to Cercospora leaf blight in these experiments, and this disease is now considered to be the most important disease problem facing Louisiana soybean producers. 2. Research on optimization of fungicide protocols will lead to science-based recommendations regarding selection of chemical classes of fungicides and rates and times of application for managing Cercospora leaf blight. 3. Given the intractable nature of Cercospora leaf blight of soybean, our findings that foliar applications of minor elements reduce disease severity will provide a powerful new weapon for managing this disease and others. We expect to develop prescription-based recommendations on the basis of plant tissue analyses conducted at specific soybean growth stages. 4. The green stem malady has become a major problem for the soybean industry. Our finding that the major component of this disorder is genetic allows us to now screen commercial varieties for their propensity to develop this syndrome under different environmental conditions. This will be done by screening varieties in field trials at one or more locations in Louisiana. 5. We completed field experiments in which we documented that Simplicillium lanosoniveum increases in population on soybean leaf surfaces in response to the presence of urediniospores of the soybean rust pathogen. Active pustules are not required to support phylloplane populations of this organism; however, its population increases dramatically after pustules emerge from infected leaf surfaces. The net effect is a reduction in numbers of pustules per unit area, a reduction in spores per uredinium and accelerated aging of rust spores in the uredinium. 6. Our surveys and extensive host range study conducted in the southern-most region of Louisiana confirmed that the unusually low temperatures during the winter of 2009/2010 essentially eradicated the soybean rust pathogen from Louisiana. We can now state with a higher degree of confidence that the threat of soybean rust for the current season is greatly minimized. Of course, inoculum can be disseminated into Louisiana from more southerly latitudes with tropical storms. 7. The cost:benefit calculator will provide a science-based tool for producers who must decide whether or not apply a fungicide at specific growth stages. This calculator will be made available on the LSU AgCenter website and developed into a smart phone application.

PUBLICATIONS (not previously reported): 2010/01 TO 2010/12
1. Boudreaux, J.M., J.L. Griffin, B.R. Leonard, R.W. Schneider, and M.E. Salassi. 2010. Value of paraquat harvest aid in soybean IPM programs. Proc. South. Weed Sci. Soc. 63:118.
2. Boudreaux, J. M., J. M., Griffin, J. L., Schneider, R. W., and Padgett, G. B. 2010. Managing Soybean Green Stem: Paraquat and Sodium Chlorate Application Affects Soybean Harvest and Yield. Southern Soybean Disease Workers, Proceedings.
3. Chanda, A. K., Chen, Z., and Schneider, R. W. 2010. Possible functions of light-induced proteins in cercosporin biosynthesis by Cercospora kikuchii. Phytopathology 100:S22
4. Padgett, G. B., Boquet, D., Schneider, R. W., and Purvis, M. 2010. The Influence of Fungicides, Herbicides, and Water Stress and Their Interactions on Green Bean Syndrome in Soybean. Southern Soybean Disease Workers, Proceedings.
5. Schneider, R. W., Padgett, G. B., Boquet, D. J., and Valverde, R. A. 2010. Factors affecting the development of the green stem malady in soybean. Phytopathology 100:S115
6. Ward, N. A., Schneider, R. W., Aime, M. C., Robertson, C. L. 2010. Leaf Surface Interactions between Phakopsora pachyrhizi, the Soybean Rust Pathogen, and the Mycoparasite Simplicillium lanosoniveum. Proceedings, The 9th International Symposium of the Microbial Ecology of Aerial Plant Surfaces. Corvallis, OR.
7. Ward, N. A., Schneider, R. W., and Robertson, C. L. 2010. Field evaluations of Simplicillium lanosoniveum as a biological control agent for Phakopsora pachyrhizi. Phytopathology 100:S134
8. Ward, N. A., Schneider, R. W., and Robertson, C. L. 2010. Field evaluations of Simplicillium lanosoniveum as a biological control agent for Phakopsora pachyrhizi. Southern Soybean Disease Workers, Proceedings.
9. Ward, N. A., Schneider, R. W., Giles, C. G., and Robertson, C. L. 2010. Development of a screening protocol for assessing baseline sensitivity to fungicides for Phakopsora pachyrhizi, the soybean rust pathogen. Phytopathology 100:S203.

PROGRESS: 2009/01/01 TO 2009/12/31
OUTPUTS: 1. We determined that there is an extended latent period after infection of soybean leaves by the soybean rust pathogen. This was assessed by collecting leaves from field-grown plants on a weekly basis and then conducting real-time PCR assays for the rust pathogen. Spore traps were monitored simultaneously so that we had an indication of when inoculum arrived in the field. Up to 60 days elapsed in one instance between inoculum arrival and symptom expression. Fungicide timing studies were conducted simultaneously, and we were able to relate fungicide efficacy to time of infection and application during the latent infection period. 2. The third and final year of our chloride amendment studies was completed. We confirmed previous findings in which we showed that chloride, regardless of the accompanying cation, suppressed the rate of increase of disease severity although final severity was not affected. 3. A geographical information systems (GIS) study was completed in 2009 in which we related soybean rust development to physical/chemical soil properties and plant nutritional analyses. Analyses are not yet complete, but it is apparent that we will be able to relate disease severity with certain soil physical and chemical parameters. Aluminum, calcium and soil strength appear to be involved in affecting disease development. 4. We developed a protocol to assess populations of the soybean rust pathogen for resistance to the commonly used fungicides. The protocol involved assessments of urediniospore germination following inoculation onto agar media amended with various concentrations of the fungicides. We standardized the methods used to recover spores from infected leaves and the method used to inoculate agar plates. Spore germination was assessed 6 hours after inoculation. 5. A newly described fungus was identified that colonized only soybean rust uredinia. Colonized uredinia produced fewer spores, and the spores that were produced were brown rather than tan. These spores had lower germination rates and were more sensitive to ultraviolet radiation. We found that this fungus is a mycoparasite in that it penetrated urediniospores and apparently parasitized them. Field inoculations with this fungus appeared to reduce pustule numbers on soybean plants. 6. The recently described green stem syndrome was examined in great detail at multiple locations in Louisiana by several investigators. We determined that the effect is driven largely by varietal differences, and that a strobilurin fungicide could cause this malady in sensitive soybean cultivars. 7. An extensive field investigation was conducted to determine the time of infection of soybean by the Cercospora leaf blight pathogen. This was accomplished by spraying plants under 12 regimens with six fungicides beginning at early vegetative growth. Results showed that infection occurs very early in the season even though symptoms are not apparent until near maturity. Molecular assays for the pathogen confirmed these findings in that fungal biomass increased for many weeks before symptoms were observed. PARTICIPANTS: Not relevant to this project. TARGET AUDIENCES: The ultimate target audience is the soybean industry and the public in general. The industry will benefit by reducing their costs for disease control and providing entirely new disease management modalities. The public will benefit by the reduced usage of fungicides. PROJECT MODIFICATIONS: Nothing significant to report during this reporting period.

IMPACT: 2009/01/01 TO 2009/12/31
1. Current dogma dictates that fungicides should be applied when first symptoms appear on nearby sentinel plants or in the commercial crop. However, we now show that this is probably too late for a single application to provide season-long control. We demonstrated that when fungicides are applied before the onset of latent infection, this single application is highly efficacious. 2. Chloride salts, potash or calcium chloride, are very inexpensive and can be applied pre-plant. This agronomic practice delays soybean rust onset and the rate of disease development. These results suggest that, under high disease pressure, a preplant application of chloride may result in fewer fungicide applications, and if disease occurs late in the season, this cultural control practice may eliminate the need for fungicides altogether. 3. The completion of our GIS project appears to have identified certain soil properties that are associated with reduced and enhanced disease development. For example, if aluminum concentrations are correlated with disease suppression, it may be possible to supplement soils with aluminum. Conversely, if other elements or soil physical conditions are associated with high disease incidence, we may be able to incorporate these agronomic practices into a disease management program. 4. One of the greatest risks associated with reliance on fungicide applications to control soybean rust is the development of resistance to the fungicide by the pathogen. We developed protocols to assess the pathogen for fungicide sensitivity, and we will assess populations of the pathogen for this trait beginning in 2010. It is important to monitor the pathogen population so that if resistance is documented, alternative fungicides should be recommended for at least that one season. We must be especially vigilant for this possibility and take every precaution to manage our fungicide arsenal effectively. 5. The unique fungus that inhabits only soybean rust uredinia was shown to reduce disease severity and spore production in the field. Our early results are very promising with regard to development of a biological control agent. Furthermore, this discovery opens an entirely new field of investigation in leaf-surface fungal ecology that should stimulate additional work by others. 6. Green stem is now ranked as one of the most important problems in the soybean industry. This collaborative effort has resulted in the identification of factors that contribute to this malady. Most importantly we showed that there is a genetic component, and this suggests that it should be possible to develop soybean cultivars that are less prone to this disorder regardless of the causal agents. 7. Cercospora leaf blight has been a steadily mounting problem for the soybean industry. This disease has been recalcitrant to fungicidal control, and this has perplexed researchers for several years. We now know that infection occurs very early in the season. In fact, there is some indication that symptomless infected seeds serve as the primary source of infection. If this proves to be correct, it may be a simple matter of producing pathogen-free seeds to manage this troublesome disease.

PUBLICATIONS: 2009/01/01 TO 2009/12/31
1. Mumma, E. P., Schneider, R. W., and Robertson, C. L. 2009. Association of specific variables with severity of Asian soybean rust as assessed by GIS analysis at the field level. Phytopathology 99:S91 (Abstr.)
2. Schneider, R. W., Haudenshield, J. S., Hartman, G. L., and Mahaffee, W. F. 2009. Development and use of fluorescent antibody and qPCR protocols for the electrostatic spore trap. Phytopathology 99:S115 (Abstr.)
3. Ward, N. A., Schneider, R. W., and Aime, M. 2009. Characterization of a co-inhabitant of uredinia of Asian soybean rust. Phytopathology 99:S138 (Abstr.)
4. Chanda, A. K., Chen, Z., and Schneider, R. W. 2009. Real time PCR based detection and quantification of Cercospora kikuchii in soybean plants. Southern Division APS. Feb 1 to 2, 2009. Atlanta, GA. meetings div so09abs.asp
5. Schneider, R. W. 2009. Foliar Diseases of Soybean in the South. On-line presentation and publication. edcenter seminars Foliar Diseases Of Soybean.
6. Cai, G., Schneider, R. W., and Padgett, G. B. 2009. Assessment of lineages of Cercospora kikuchii in Louisiana for aggressiveness and screening soybean cultivars for resistance to Cercospora leaf blight. Plant Disease 93:868-874.
7. Chanda, A. K., Z. Chen, Z., and Schneider, R. W. 2009. Comparison of protein profiles between light and dark grown Cercospora kikuchii. Phytopathology 99:S20 (Abstr.)
8. Schneider, R. W. 2009. Asian soybean rust four years later: Is the disease a nonstarter or are we still at risk Southern Division APS. Feb 1 to 2, 2009. Atlanta, GA. meetings div so09abs.asp
9. Ward, N. A., Schneider, R. W. and Aime, M. C. 2009. Uredinia of Asian soybean rust as a unique niche for other fungi. Southern Division APS. Feb 1 to 2, 2009. Atlanta, GA. meetings div so09abs.asp
10. Ward, N. A., Schneider, R. W., and Brown, M. 2009. Mycoparasitism of Phakopsora pachyrhizi by Simplicillium lanosoniveum. 2009 National Soybean Rust Symposium, Proceedings. infocenter topic soybeanrust 2009 posters 10.asp.
11. Schneider, R. W., Ward, N. A., Robertson, C. L., and Mumma, E. P. 2009. Latent infection, fungicide efficacy and the need for predictive models. 2009 National Soybean Rust Symposium, Proceedings. infocenter topic soybeanrust 2009 presentations Schneider.pdf


Name: Schneider, R. W.
Phone: 225-578-1366
Fax: 225-578-1415
7/20/2011 9:14:56 PM
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