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ACCESSION NO: 0194020 SUBFILE: CRIS
PROJ NO: LAB93591 AGENCY: CSREES LA.B
PROJ TYPE: HATCH PROJ STATUS: NEW
START: 01 OCT 2002 TERM: 30 SEP 2007 FY: 2004
INVESTIGATOR: Schneider, R. W.
PERFORMING INSTITUTION:
PLANT PATHOLOGY & CROP PHYSIOLOGY
LOUISIANA STATE UNIVERSITY
BATON ROUGE, LOUISIANA 70893
Biology and Management of Soybean Diseases in Louisiana
NON-TECHNICAL SUMMARY: Diseases are a major constraint to maximizing yield and profitability in soybeans in Louisiana. Because of the climate in the mid-Gulf region, some of these diseases, which may be of minor importance in other soybean production areas, are very damaging here. The purpose of this project is to find the most efficacious means for controlling diseases in soybean. These include screening of new fungicides and development of fungicide application protocols; evaluation of cultural control programs; and screening and development of disease resistant varieties.
OBJECTIVES: 1. To assess damage caused by common soybean diseases 2. To develop disease severity and yield loss forecasting models for selected diseases. 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.
APPROACH: Objectives 1 and 2 In general, two treatments will be inluded in field experiments in which the disease of interest is controlled in one treatment with appropriate fungicides and disease is allowed to develop in the other treatment; yields are then compared. However, specific soybean varieties are susceptible to multiple diseases. It then becomes problematic to separate the effects of all these diseases. One solution to this problem is to include many varieties in each of the two treatments. 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. Objective 3 Varieties will be evaluated for disease reactions at multiple locations. Fungicides will be screened for efficacy in controlling diseases in statewide field trials. More detailed information, rates and times of application, particularly with new compounds, will be developed in replicated field experiments at the Ben Hur Research Farm and other research stations in collaboration with other scientists. A disease resistance breeding program will be initiated. It is anticipated that portions of the world soybean germplasm collection will be screened for resistance to our more severe diseases. If sources of resistance can be found, these lines will be submitted to existing breeding programs, and attempts will be made to determine modes of inheritance. Objective 4 One of the enduring problems associated with developing disease resistant varieties is the constantly changing genetic make-up of pathogen populations. Strains of pathogens will be collected from soybeans in variety trials and culture collections will be maintained. Individual isolates will then be tested in the greenhouse or in detached leaf cultures to assess their range of virulence on selected varieties. Predominant strains will be subjected to molecular analyses, including sequencing of rDNA segments, which will serve as fingerprint baselines for future surveys. As new strains are found, they will be tested against commonly used varieties. Knowledge of disease cycles often leads to disease management strategies. We know very little about alternate hosts or sources of inoculum for such pathogens as Diaporthe and Phomopsis, the two Cercospora species, and the anthracnose pathogen. Interactions with other pests also must be considered. Recent collaborative work with the soybean entomology program provides strong evidence that there is a significant interaction between aerial blight and stink bugs. In addition, this interaction may play a role in the delayed maturity, or green bean, syndrome.
PROGRESS: 2004/01 TO 2004/12
A tank mix of the fungicides Topsin M (8 oz.) and Quadris (4 oz.) applied either at R3 or R3 and R6 was the most effective treatment for the control of Cercospora leaf blight and frogeye on two soybean varieties that were chosen as highly susceptible to these two diseases. These two fungicides are registered for use on soybean. There was about a 19% yield increase with this treatment as compared to a nontreated control. In addition, there was significantly less seed discoloration and shriveling (weathering) in the harvested grain from this treatment following a delayed harvest. These findings are noteworthy, because grain weathering is a recurring problem in the midsouth, particularly when the region is exposed to heavy rains associated with hurricanes. These conditions provide ideal conditions for infection by seed decay organisms and also prevent growers from harvesting for extended periods because their fields may be too wet for harvesting equipment. The fungicide Headline (10 oz.) was effective in controlling Cercospora leaf blight. The fungicide Quilt was intensively evaluated in 2004. This material is a mixture of a strobilurin (Quadris) and propiconazole (Tilt). This fungicide is of particular interest because it combines curative and protective materials that are effective against soybean rust. Quilt was very effective against Cercospora leaf blight and frogeye leaf spot, and it resulted in approximately a 15% yield increase and an improvement in grain quality. This completes the third and final year of field trials for the soybean yield loss forecasting model related to Cercospora leaf blight, frogeye leaf spot, aerial blight, and pod and stem diseases. As a proof of concept, portions of the extensive data set were used to generate yield loss prediction equations for frogeye and Cercospora leaf blight when disease severity was assessed at R3. Numerous equations are being evaluated for best fit, and following are two that had high coefficients of correlation. Frogeye: A logistic dose response curve in which a=78.99, b=17.66, c=-1.84 Cercospora leaf blight: y=a+bx*2+cx*4+dx*6, where x=disease severity, a=-0.5756, b=0.3589, c=0.00191, and d=-5.5349. Nearly 350 soybean varieties were evaluated for disease resistance at two locations in Louisiana. Most maturity group IV varieties were highly resistant to frogeye and Cercospora leaf blight. However, most varieties in maturity groups V and VI were highly susceptible to these two diseases. Results from molecular population genetics studies of Cercospora kikuchii suggested that this pathogen has broadened its pathogenicity against formerly resistant varieties and that the pathogen probably has a covert sexual stage that may be responsible for the extremely high level of genetic diversity within the population.
IMPACT: 2004/01 TO 2004/12
Results from this project provide ample documentation that a combination of Topsin M and Quadris at below label rates provided a substantial degree of control of Cercospora leaf blight and frogeye. In recent years, this disease has assumed epidemic proportions in Louisiana and is now the most prevalent disease. Furthermore, we demonstrated that the pathogen is capable of developing new strains or races quickly, and there is little disease resistance in maturity group V and VI commercial varieties. This latter finding may be significant if it is found that late plantings are recommended for cultural control of soybean rust. The disease loss prediction models will be useful for making cost/benefit decisions regarding the application of fungicides for control of the major foliar diseases.
PUBLICATIONS: 2004/01 TO 2004/12
1. Cai, G. and Schneider, R. W. 2004. Population structure of Cercospora kikuchii from soybean. Phytopathology 94:S13 (Abstr.).
2. Kuruppu, P. U., Schneider, R. W., and Russin, J. S. 2004. Factors affecting soybean root colonization by Calonectria ilicicola and development of red crown rot following delayed planting. Plant Disease 88:613-619.
3. Kuruppu, P. U., Schneider, R. W., and Russin, J. S. 2004. Effects of soil temperature on microsclerotia of Calonectria ilicicola and soybean root colonization by this fungus. Plant Disease 88:620-624.
4. Callahan, S. D., and Schneider, R. W. 2004. Pathogenicity of selected fungi on Spartina alterniflora and their possible role in Louisiana marsh dieback. Phytopathology 94:S13 (Abstr.).
5. Schneider, R. W. 2004. Preservation of soybean seed quality with foliar fungicide application. Louisiana Soybean and Feed Grain Review 2(7):2.
6. Schneider, R. W., Judice, W. E., Jones, C. A., and Griffin, J. L. 2004. Effects of fungicides on seed weathering in soybean. Louisiana Plant Protection Assoc., Proceedings.
7. Cai, G., and Schneider, R. W. 2004. Population structure of Cercospora kikuchii as assessed with vegetative compatibility groups and DNA fingerprints. Page 10 in: Southern Soybean Disease Workers, Proceedings.
8. Schneider, R. W. 2004. Effect of fungicides on soybean grain quality following delayed harvests. Page 12 in: Southern Soybean Disease Workers, Proceedings.
PROJECT CONTACT:
Name: Schneider, R. W.
Phone: 225-578-1464
Fax: 225-578-1415