PROJECT RESULTS

Fusarium Head Blight Resistant Winter Wheat Germplasm Development

Dr. A.L. Brűlé-Babel

Department of Plant Science

University of Manitoba

Winnipeg, Manitoba  R3T 2N2  Canada

Table of Contents:

• Background and Objectives
• Procedure and Project Activities
• Results and Discussion
• Conclusion

Dr. A.L. Brűlé-Babel and Dr. W.G.D. Fernando, Department of Plant Science, University of Manitoba

ARDI Project:

#98-186

Project Status:

Completed March, 2003

Background and Objectives:

Since 1992 fusarium head blight (FHB) has caused significant losses in spring wheat crops across Manitoba.  Losses occur as a result of reductions in yield and end-use marketability of the crop.  Of particular concern is the presence of mycotoxins such as deoxynivalenol (DON or vomitoxin) which severely limit the use of the crop for food, feed and ethanol production.  Fusarium graminearum is the main causal agent of FHB in wheat in Manitoba. Although winter wheat tends to escape FHB infection in most years, hot, humid conditions during flowering in 1998 led to high levels of FHB in some fields.  This indicated that FHB could not be ignored in winter wheat and that efforts to breed FHB resistance into winter wheat should be considered.  In addition very little was known about the reaction of winter wheat cultivars to FHB, as no testing had been conducted in Manitoba.  Until resistant cultivars are available, producers need basic information on the efficacy of fungicides for FHB control and the potential for combined control of leaf diseases and FHB.  Therefore, the objectives of this study were to:

1. Determine the FHB reaction of registered cultivars of winter wheat.
2. Develop FHB resistant winter wheat germplasm.
3. Evaluate FHB and leaf disease incidence of several winter wheat cultivars under different fungicide treatments.

Procedure and Project Activities:

The objectives of this project were met through three different sets of experiments.

Cultivar Evaluation

To compare the FHB response of registered winter wheat cultivars and lines entered into the Central Winter Wheat Cooperative trial (variety registration trials), cultivars and lines were evaluated at two locations, Winnipeg and Carman, in 2000, 2001 and 2002.  The experimental design of each trial was a four replicate randomized completed block.  Plots were single 3 m rows representing each cultivar or line.  Plots were inoculated with F. graminearum at anthesis and four days after anthesis.  Spikes were collected 18-21 days after inoculation and evaluated for % infected heads (incidence) and % infected spikelets (severity).  From these measurements a FHB Index ((incidence X severity)/100) was calculated for each cultivar/line.

Germplasm Development

Several sources of FHB resistant germplasm were obtained from Canada, the US and China.  These sources were used as parents in crosses with adapted winter wheat cultivars and advanced breeding lines from the winter wheat breeding program.  Crosses were made in 2000.  F₁ plants from seven crosses were planted in 2001, vernalized and directed to the production of doubled haploids.  Approximately 1000 doubled haploids were produced.  Doubled haploids were the primary focus of this work because the complex inheritance of FHB resistance makes it very difficult to identify recombinants with the maximum number of resistance genes through conventional breeding techniques.  Seed of the doubled haploids was increased and screening is being conducted to identify FHB resistant doubled haploid lines.  Lines identified as resistant are being backcrossed to their adapted parent to reconstitute the majority of traits from the adapted parent.  This is necessary because all of the sources for resistance for FHB are relatively unadapted wheat lines.  As crosses are completed another round of doubled haploid production and selection will be initiated.  This work is ongoing and will take several years to complete.

Fungicide Trials

The first part of this study was conducted in the summer of 1999 to evaluate the effect of different fungicide treatments on FHB and leaf spotting diseases in a number of winter wheat cultivars.  The treatments included inoculated and un-inoculated controls, Tilt, Folicur and Bravo applied at the time recommended on the label for leaf disease control (Tilt), or FHB control (Folicur and Bravo), combinations of Tilt + Folicur, Tilt + Bravo and two applications of Bravo.   All plots receiving fungicide treatment were also inoculated with a conidial suspension of F. graminearum in the same manner as described above for the cultivar evaluation trials.  Ten different winter wheat cultivars or lines were evaluated under the different fungicide treatments in a four replicate split plot design.  In 2000, 2001 and 2002 a similar experiment was conducted at two locations (Carman and Winnipeg) except that only one wheat cultivar, CDC Falcon, was used in this study.  CDC Falcon was chosen because it appeared to be one of the most FHB susceptible cultivars in the 1999 study.  Eighteen to 21 days after each inoculation spikes were collected and % infected spikes (incidence) and % infected spikelets (severity) were determined.  From these measurements a FHB Index ((incidence X severity)/100) was calculated for each cultivar/line.  In addition, flag leaves and the penultimate leaves were collected to determine, through digital analysis, the % leaf area affected by leaf diseases.  Yield, thousand kernel weight, and % Fusarium Damaged Kernels (%FDK) were also determined.

Results and Discussion:

The results from cultivar evaluation trials and fungicide trials indicated that even with inoculation and provision of mist irrigation to maintain a high relative humidity, infection of winter wheat with F. graminearum was not always effective.  Analysis of night time temperatures indicated that when night temperature fell below 10 ^oC during the time of flowering and inoculation, infection with FHB was low.  This suggests that disease forecasts that predict the potential for FHB infection need to consider night time temperature in addition to day time temperature and humidity to provide a reliable estimate of potential disease epidemics in winter wheat.

Cultivar Evaluation Trials

The cultivar evaluations trials showed that most of the cultivars grown in western Canada had FHB reactions similar to the moderately resistant to moderately susceptible checks.  Therefore, most of the winter wheat cultivars do not appear to be as sensitive to FHB as cultivars obtained from eastern Canada.  Three cultivars, CDC Falcon, CDC Raptor, and McClintock occasionally produced FHB responses similar to the susceptible checks, but these results were not consistent across the different trials. Further work is required to determine if these cultivars are truly more sensitive to FHB than the other cultivars evaluated.

Germplasm Development

The winter growth habit of winter wheat makes germplasm development a very time consuming process.  Nevertheless, parental genotypes were evaluated, crosses were made, double haploids were produced, seed was increased and screening and backcrossing are being completed.  Some highly resistant doubled haploids were identified through the screening process indicating that FHB resistance was successfully captured.  This work is ongoing and will take several years to complete.

Fungicide Trials

The results from the 1999 trial showed good control of leaf diseases, including leaf rust and leaf spotting diseases, for the fungicide treatments that included Tilt and to a lesser extent, Folicur.  The best control of leaf diseases was obtained from the combined Tilt + Folicur treatment.  This translated into improved yield. Control of FHB was more variable. In general Bravo and Folicur provided similar levels of FHB control.  Correlation analysis revealed that yield differences were associated with differences in leaf disease control, not FHB control.

The results from the 2000, 2001 and 2002 trials indicated that significant differences were not consistently observed among treatments for all characteristics measured in all years and locations.  In most cases, fungicide application reduced the FHB Index relative to the inoculated control, but with the exception of the Winnipeg 2001 site, none of the treatments improved FHB Index to the level of the un-inoculated check.  In general, treatments with either Bravo or Folicur produced similar results and reduced FHB infections when compared to the inoculated check.  Two applications of Bravo did not improve FHB Index.  As would be expected, FHB levels on treatments with Tilt alone were similar to the inoculated control.  Combination treatments with Tilt and either Folicur or Bravo produced variable results, but in general did not improve the FHB Index relative to single applications of either Folicur or Bravo.  The results from this study showed that Folicur and Bravo can reduce FHB Index under some situations, but when FHB levels are high, such as the 2002 trials, the reduction in FHB Index may not be sufficient to reduce losses to FHB.

Overall, the fungicide treatments did not reliably reduce %FDK to the level of the un-inoculated control and in most cases provided only a marginal improvement in %FDK relative to the inoculated control.  Therefore, although fungicide applications may appear to reduce the symptoms of FHB found on the spike, they may not lead to an improvement in the grade achieved when the grain is sold. 

Although control levels were variable, most fungicide treatments provided some level of leaf disease control over the untreated checks.  Tilt and Folicur provided similar levels of control in most cases, while Bravo provided varying levels of leaf disease control.  Even though Folicur was applied at heading to control FHB (not the optimum time for leaf disease control), this late application provided some protection to the crop.  Therefore, if FHB control is of concern, and leaf disease incidence is low at flag leaf emergence, delaying fungicide application by using Folicur at heading may provide adequate protection from leaf disease pathogens. 

Significant yield differences among the treatments were only observed in 1999 and in Winnipeg 2001.  Therefore, despite relatively high FHB levels in 2002, fungicide treatments had little impact on yield.  When yield was significantly different among treatments, there was a higher association between yield and leaf diseases than between yield and FHB Index.

Conclusion:

The results from this study showed that commercial winter wheat cultivars are not resistant to FHB, but that most cultivars were similar to the moderately resistant to moderately susceptible checks.  This suggests that efforts to improve FHB resistance are worthwhile.  This project facilitated the initial stages of germplasm development. Screening of doubled haploid lines for reaction to F. graminearum indicated that transfer of resistance to adapted cultivars will be possible.  However, development of resistant cultivars will take a number of years. 

Under high disease pressure, fungicide treatments reduced levels of leaf rust, leaf spot and FHB, and improved yield.  Fungicide treatments provided little yield advantage under low disease pressure.  Under high disease pressure fungicide treatments with either Bravo or Folicur reduced FHB Index.  However, the FHB Index of these treatments was still high relative to the un-inoculated control.  Based on this, it is questionable whether fungicides can provide sufficient protection from FHB under high disease pressure to significantly improve the grade and marketability of the grain.  When either leaf rust or leaf spotting diseases were present, treatments with Tilt and to a lesser extent, Folicur reduced these diseases.  Overall, there was no association between yield and FHB Index.  Leaf diseases appeared to be the main cause of yield differences observed.

The results from this study indicate that even with inoculation and provision of mist irrigation, infection of winter wheat with F. graminearum was not always effective.  This, along with the variable results from the fungicide treatments suggests that continued efforts to refine disease forecasting may be beneficial to producers. 

Acknowledgements:

This project was made possible due to funding from the Government of Manitoba and Canada through the Canada-Manitoba Agri-Food Research and Development Initiative (ARDI), the Western Grains Research Foundation and Canterra Seeds Ltd.

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