Published online 5 January 2006
Published in Agron J 98:194-197 (2006)
DOI: 10.2134/agronj2005.0094
© 2006 American Society of Agronomy
677 S. Segoe Rd., Madison, WI 53711 USA
Production Papers
Integrated Use of Tebuconazole and Fusarium Head Blight–Resistant Barley Genotypes
R. D. Horsleya,*,
J. D. Pedersona,
P. B. Schwarza,
K. McKayc,
M. R. Hochhalterd and
M. P. McMullenb
a Dep. of Plant Sciences, North Dakota State Univ., Fargo, ND 58105-5051
b Dep. of Plant Pathology, North Dakota State Univ., Fargo, ND 58105
c North Central Research Extension Center, Minot, 58702
d Dep. of Plant Sciences, North Dakota State Univ., Fargo, ND 58105-5051
* Corresponding author (richard.horsley{at}ndsu.edu)
Received for publication April 1, 2005.
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ABSTRACT
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All malting barley (Hordeum vulgare L.) cultivars adapted for production in the upper midwestern USA are susceptible to Fusarium head blight (FHB), incited primarily by Fusarium graminearum Schwabe [teleomorph Gibberella zeae (Schwein)]. Quality of FHB-infected barley is reduced due to a mycotoxin called deoxynivalenol (DON) that is produced by the pathogen. Malting barley buyers severely discount or refuse to purchase barley with DON concentrations >0.5 mg kg–1. Individually, use of genetic resistance or fungicides has not successfully reduced DON concentrations to acceptable limits. The objective of this research was to determine if the integrated use of the fungicide tebuconazole (
-[2-(4-chlorophenyl) ethyl]--(1,1-dimethylethyl)-1H-1,2,4-triazole-1-ethanol) and barley genotypes with partial FHB resistance could reduce DON to acceptable concentrations. Field research, using two rates of tebuconazole (0 and 118 mL a.i. ha–1) and 13 barley genotypes with varying levels of FHB resistance, was conducted in North Dakota from 2000 to 2002. No supplemental inoculum or irrigation was used in any of the environments. Data for FHB severity, DON concentration, foliar disease severity, and kernel color were collected and analyzed. Deoxynivalenol was detected in all environments at concentrations >0.5 mg kg–1. Overall, the response of the FHB-resistant and moderately resistant genotypes to tebuconazole was inconsistent for FHB severity and DON accumulation. Furthermore, tebuconazole applied to FHB-resistant or moderately resistant genotype did not consistently result in DON concentration of 
0.5 mg kg–1 in any of the environments. Thus, the integrated use of FHB-resistant or moderately resistant genotypes and tebuconazole will not reduce DON.
Abbreviations: ANOVA, analysis of variance • DON, deoxynivalenol • FHB, Fusarium head blight • GAO, Government Accounting Office
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INTRODUCTION
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FUSARIUM HEAD BLIGHT has adversely affected the quality of barley grown in eastern North Dakota and northwestern Minnesota every year since 1993. Quality of harvested grain was reduced because of blighted kernels and the presence of deoxynivalenol (DON), a mycotoxin produced by the pathogen F. graminearum. Nondetectable or low levels of DON are needed for malting barley because DON has been found to carry through malting and brewing into finished beer (Schwarz et al., 1995). Hence, barley with >0.5 mg kg–1 is rejected or heavily discounted by the malting and brewing industries. Barley growers have experienced significant revenue losses due to DON since they cannot realize malting barley premiums and must sell their barley as feed. The U.S. Government Accounting Office (GAO) estimates that losses in North Dakota from 1993 to 1997 due to FHB of barley were about $200 million (GAO, 1999). This amount is equal to about 17% of the $1.2 billion in total barley revenues that North Dakota growers received during this period.
Research to test the efficacy of fungicides in reducing FHB and DON levels in barley has been conducted using cultivars susceptible to FHB. Pederson and McMullen (1999) found that several fungicides, including tebuconazole, significantly reduced FHB severity and DON content of barley. However, the fungicides were not successful in reducing DON concentration to a level that would be acceptable to maltsters and brewers. Deoxynivalenol levels were high in all treatments and the most successful fungicide treatment only reduced DON content of barley to 17.2 mg kg–1.
Urrea et al. (2005) tested more than 30 barley accessions with the highest levels of FHB resistance. None of the accessions was immune to the disease and all accumulated excessive DON concentrations under severe disease conditions. During the next 5 to 10 yr, malting barley cultivars with improved FHB resistance will be released by breeding programs in the upper midwestern USA. These improved cultivars will be developed using the FHB-resistant accessions tested by Urrea et al. (2005); however, the genetic resistance incorporated into these cultivars will not be sufficient to prevent excessive DON concentrations in many environments. Growers will likely need to use an integrated approach that utilizes resistant cultivars, fungicides, and cultural control methods to increase their chance of producing barley that meets the specifications of the malting and brewing industries.
To date, no research has been conducted to determine if the combined use of resistant cultivars and fungicides can work to successfully reduce FHB severity and DON accumulation. This article reports on our research to determine if the integrated use of the fungicide tebuconazole and resistant or moderately resistant barley genotypes will reduce FHB severity and DON accumulation to levels acceptable to the malting and brewing industry.
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MATERIALS AND METHODS
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Thirteen barley genotypes with different levels of FHB resistance were used in this study. Genotypes in the FHB resistant class were ‘Chevron’, ‘Kaoto Nijo’, and ‘Svanhals’; the moderately FHB-resistant class included F101-78, F102-61, F103-61, and ‘MNBrite’; and the susceptible class included the cultivars Conlon, Drummond, Foster, Legacy, Logan, and Stander. Assignment of genotypes to the classes was based on FHB severity data from previous research (Urrea et al., 2005; Prom et al., 1996).
The field experiments were conducted at five environments in North Dakota from 2000 to 2002. In 2000 the experiment was conducted at Fargo and Osnabrock; in 2001 the experiment was conducted in Langdon and Osnabrock; and in 2002 the experiment was conducted at Osnabrock. The soil at Fargo is a fine-silty, frigid Typic Calciaquoll; the soil at Langdon is a fine, montmorillonitic, Utric Natriboroll; and the soil at Osnabrock is a fine, montmorillonitic, frigid Typic Haploboroll. No supplemental inoculum or irrigation was provided at any environment to increase the severity of the disease.
Treatments were assigned to 3.26 m2 (3.05 by 1.07 m) experimental units using a randomized complete block design with a split-plot arrangement. Each treatment was replicated three times. Whole plots included two levels of the fungicide treatment, no fungicide or 110 mL ha–1 of tebuconazole, and subplots were the 13 genotypes. Tebuconazole was applied at Feeke's growth stage 10.3 using a CO2–pressurized handheld boom sprayer operating at 275 kPa, and calibrated to deliver 187 L of solution ha–1.
Foliar disease and FHB severity were determined at Feeke's growth stage 11.2. Foliar disease severity was recorded using a 1 to 9 foliar disease score, with 1 = no disease and 9 = severe disease. The foliar disease score was visually determined and based on the general level of disease severity on the foliage of all the plants in the experimental unit and not on individual diseases. Fusarium head blight severity was measured by determining the ratio of infected kernels to total kernels on 10 spikes per experimental unit. Disease severity was expressed as percentage FHB severity (e.g., if six kernels on a spike containing 60 kernels were symptomatic, the FHB severity would be recorded as 10%). At maturity, each experimental unit was harvested with a small-plot combine. Grain samples were dried and cleaned before DON and kernel brightness determination. Deoxynivalenol content (mg kg–1) was determined using the methodology described by Schwarz et al. (1995). Kernel brightness was measured by determining the L value using a Hunter LB XL-800 series colorimeter (Gardner Laboratories Division, Bethesda, MD).
Data from individual environments were analyzed separately using analysis of variance (ANOVA). Error mean squares from each environment were tested for homogeneity of variance, and combined ANOVA were conducted using data from environments in which error mean squares were homogeneous. Means were separated using an F-protected LSD (P = 0.05). In the combined analyses, fungicide and genotypes were considered fixed effects and environment a random effect.
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RESULTS
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The environment x fungicide x genotype interaction was nonsignificant (P > 0.05) for DON concentration and L value, and significant (P 0.05) for FHB severity and foliar disease score. Upon investigation of the means it was determined that the significance of the F tests was due to differences in magnitude of the means between environments and not differential responses of the treatments in the different environments. Thus, it was appropriate to evaluate the genotype x fungicide interaction.
Fusarium Head Blight Severity
Mean FHB severity was lowest at 2000 Fargo (0.8%), with a range of 0.0 to 4.3%, and greatest at 2000 Langdon (4.9%), with a range of 0.0 to 13.1%. The fungicide x genotype interaction was not significant (P > 0.05), indicating that genotypes responded similarly to the fungicide treatments. The main effect for fungicide was significant (P < 0.05) and the main effect for genotypes was nonsignificant (P > 0.05). Averaged across environments and genotypes, mean FHB severity was 3.0 and 2.4% for untreated and treated plots, respectively (Table 1). Averaged across environments and fungicide treatments within a FHB-resistance class, mean FHB severity was 1.9% for the resistant class, 2.4% for the moderately resistant class, and 3.3% for the susceptible class.
Deoxynivalenol Concentration
Mean DON concentration ranged from 0.3 mg kg–1 at 2000 Fargo to 1.8 mg kg–1 at 2001 Osnabrock. Maximum DON concentration ranged from 1.1 mg kg–1 at 2000 Fargo to 5.1 mg kg–1 at 2001 Osnabrock. Thus, DON concentrations above the 0.5 mg kg–1 level desired by the malting and brewing industries were found at all environments.
The fungicide x genotype interaction was nonsignificant for DON concentration (P > 0.05), indicating that all cultivars responded similarly to the fungicide treatments. The fungicide main effect was nonsignificant (P > 0.05) and the genotype main effect was highly significant (P < 0.001) (Table 2).
Foliar Disease
No foliar disease was found on the plants at 2000 Fargo due to unfavorable conditions for their development. At the other four environments, foliar diseases found on the plants included spot blotch [incited by Bipolaris sorokiniana (Sacc.)], net blotch (incited by Pyrenophora teres Drechs.), and Septoria speckled leaf blotch (incited primarily by Septoria passerinii Sacc.). Mean disease scores across treatments were lowest at 2001 Osnabrock (2.6) and greatest at 2000 Langdon (4.9).
The fungicide x genotype interaction was nonsignificant (P > 0.05), indicating that the genotypes responded similarly to the application of tebuconazole. The fungicide main effect was highly significant (P < 0.01). Averaged across environments and genotypes, application of tebuconazole reduced the mean foliar disease score from 4.6 to 3.1 (Table 1). The main effect for genotype also was significant (P < 0.05). MNBrite tended to have the lowest mean foliar disease score (2.8), and F102-61 and Kaoto Nijo tended to have the highest mean disease scores (4.9) (Table 2).
Kernel Brightness (L value)
Fusarium head blight causes a discoloration of the kernel; thus, kernels infected with FHB would be expected to have a lower L value, or less brightness, than uninfected barley. The L values can range from about 30, representing very poor color to 60 for very bright kernels. Mean L value ranged from 48.9 at 2001 Osnabrock to 53.9 at 2000 Fargo. The fungicide x genotype interaction was nonsignificant (P > 0.05). The fungicide main effect was nonsignificant (P > 0.05). The genotype main effect was highly significant (P < 0.01). In general, the genotypes in the resistant and moderately resistant class had higher L values (i.e., brighter kernels) than genotypes in the susceptible class. Averaged across environments and fungicide treatments, F102-61 had the highest L value (53.6) and Foster had the lowest value (49.8) (Table 2).
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DISCUSSION
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Our experiment relied on natural conditions for the development of FHB. We felt that conducting the experiments under natural conditions would provide a better representation of what growers would experience in their own barley fields. Field locations chosen represent areas in North Dakota where barley had been most severely affected by FHB. The genotypes evaluated were chosen to provide at least three representative genotypes in each of the FHB severity classes (i.e., resistant, moderately resistant, and susceptible). Chevron, Kaoto Nijo, and Svanhals were in the resistant class; and F101-78, F102-61, F103-61, and MNBrite were in the moderately resistant class. For these two classes, only MNBrite was adapted for production in the upper midwestern USA. Characteristics limiting adaptation and/or acceptance in the other genotypes were excessive height, weak straw, later relative maturity, and poor malt quality (Urrea et al., 2005). Since the genotypes in the FHB-resistant and moderately resistant classes are being incorporated into midwestern germplasm by several barley breeding programs, we chose these genotypes to serve as a model for the level of potential resistance future adapted cultivars may have. If the genotypes we chose for this experiment responded favorably to the fungicide tebuconazole, one could hope that adapted FHB- or moderately FHB-resistant cultivars would respond similarly.
Data on yield, test weight, kernel weight, kernel plumpness, and other malt quality traits were collected; however, they were not discussed because results were confounded because the genotypes in the resistant and moderately resistant genotype classes were not adapted for production in North Dakota. The traits discussed—FHB severity, DON concentration, foliar disease severity, and kernel color—were not affected by the adaptation of the genotypes.
The goal of any chemical control program for FHB of barley is to reduce the disease sufficiently so that DON is accumulated at levels 0.5 mg kg–1. The maltster and brewer consider DON greater than this level to be a sign that the barley may not produce acceptable malt. The response of the genotypes to tebuconazole was inconsistent for FHB severity, DON concentration, foliar disease score, and kernel brightness. Thus, no general conclusion can be made on the likelihood that tebuconazole will reduce FHB severity or DON concentration to acceptable levels in the resistant or moderately resistant genotypes. However, the general trend that tebuconazole reduced FHB severity and DON concentration provides some hope that an integrated approach of resistant cultivars and fungicides may show some promise. Finally, application of tebuconazole cannot be relied on to improve kernel brightness.
Research by Schwarz et al. (2005) stated that the DON concentration limit of 0.5 mg kg–1 is too low if other barley quality traits are acceptable. They determined that the DON concentration limit could be raised to <1.0 mg kg–1 if the barley had test weight >59.2 kg hL–1, kernel plumpness >70%, grain protein <135 g kg–1, and percentage FHB severity <10. For any barley sample meeting these criteria and a DON concentration <1.0 mg kg–1, they determined that the resultant malt quality was likely to be acceptable. If the barley sample was deficient in any one of these traits, the resultant malt would have a higher probability of being unacceptable.
For our study, all genotypes in the resistant and moderately resistant classes had DON concentrations <1.0 mg kg–1 when treated with tebuconazole (Table 3). However, these values were not significantly less than those for the respective control treatment. Thus, a conclusion that the integrated use of FHB-resistant or moderately resistant genotypes and tebuconazole will consistently reduce DON cannot be made. It is our hope that in the near future an acceptance by the malting and brewing industries of a rejection DON limit of 1.0 mg kg–1 and integrated use of resistant cultivars and fungicides more effective than tebuconazole will allow growers to more consistently produce malting quality barley in the upper midwestern USA.
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Table 3. Effect of tebuconazole and genotype on deoxynivalenol (DON) concentration (mg kg–1) of barley genotypes classified as FHB-resistant, moderately FHB-resistant, or FHB-susceptible.
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ACKNOWLEDGMENTS
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The authors thank Messrs. Jason Faller and Sun Yongliang for their assistance with the FHB disease nurseries. The authors also would like to express their thanks for funding provided by the USDA-ARS National Wheat and Barley Scab Initiative.
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REFERENCES
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- General Accounting Office. 1999. U.S. agriculture: Grain fungus creates financial distress for North Dakota barley producers. GAO/RCED-99-59. U.S. Gov. Print. Office, Washington, DC.
- Pederson, J., and M. McMullen. 1999. Evaluation of fungicides for control of Fusarium head blight (FHB) in barley. p. 244. In R.N. Reid (ed.) Fungicide and nematicide tests. Vol. 54. APS Press, St. Paul, MN.
- Prom, L.K., B.J. Steffenson, B. Salas, J. Moss, T.G. Fetch, Jr., and H.H. Casper. 1996. Evaluation of selected barley accessions for resistance to Fusarium head blight and deoxynivalenol concentration. p. 764–766. In G. Scoles and B. Rossnagel (ed.) Proc. of the V Int. Oat Conf. & VII Int. Barley Symp. Univ. of Saskatchewan, SK, Canada. 30 July–6 Aug. 1996. University Extension Press, Saskatoon, SK, Canada.
- Schwarz, P.B., H.H. Casper, and S. Beattie. 1995. The fate and development of naturally occurring Fusarium mycotoxins during malting and brewing. J. Am. Soc. Brew. Chem. 53:121–127.
- Schwarz, P.B., R.D. Horsley, B.J. Steffenson, B. Salas, and J.M. Barr. 2005. Quality risks associated with the utilization of Fusarium Head Blight infected malting barley. J. Am. Soc. Brew. Chem. 63(3) (in press).
- Urrea, C.A., R.D. Horsley, B.J. Steffenson, and P.B. Schwarz. 2005. Agronomic characteristics, malt quality, and disease resistance of barley germplasm lines with partial Fusarium head blight resistance. Crop Sci. 45:1235–1240.[Abstract/Free Full Text]
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ABSTRACT
INTRODUCTION
, deoxynivalenol (DON) concentration (mg kg–1), foliar disease score
, and kernel brightness (L value
) of barley averaged across genotypes and environments.