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Results of Funded Research

Screening Soft Red Winter Wheat Varieties and Breeding Lines for Head Scab Resistance

Dave VanSanford
University of Kentucky

Objectives
Project Overview
Final Report and Data (April 1998)
Final Report and Data (April 1999)

Objectives:

To identify varieties or breeding lines that show resistance to Fusarium graminearum, the causal agent of head scab. Specific objectives include:

• to evaluate resistance among adapted wheats to initial infection by Fusarium

• to evaluate resistance among adapted wheats to the spread of infection throughout the head

• to evaluate these components of resistance in Chinese wheats from Shandong province, PRC

• to continue to evaluate inoculation methods and evaluation methods

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Project Overview:

Justification for Research

In 1991, Fusarium head blight, or head scab, caused losses approaching $50 million in the SRW wheat crop in Kentucky and much of the eastern wheat region. Since that year, we have not had an epidemic in Kentucky, although in 1995 we observed serious scab problems in several Kentucky counties, and in 1996, the problem was widespread throughout the state. In central Kentucky in 1997, head scab was a serious problem.

Conservation tillage has been cited as a major reason for the increased incidence of head scab in the HRS and SRW wheat crops. Given that the goal of the KySGGA is 75% no-till wheat by 2005, it is reasonable to assume that head scab will continue to be a major problem in Kentucky.

Head scab can greatly reduce wheat profitability through yield and test weight losses. Additional losses in food and feed quality occur through the production of mycotoxins which can cause livestock toxicosis or feed refusal. Grain with mycotoxins may be severely downgraded or rejected entirely in commerce.

Resistance to Scab

As an indication of how serious this problem is, virtually all of the breeding programs from Kentucky north are working on head scab resistance. There appear to be two components of resistance: 1) initial resistance to infection and 2) resistance to the spread of the fungus through the wheat head (Bai and Shaner, 1994, Plant Disease 78:760). Initial resistance to infection is thought to be controlled by many genes (difficult to breed for, like yield), while resistance to spread of infection may be under the control of a few genes (easier to select for). Chinese wheats such as Sumai 3 and Ning 7840 are widely regarded as the most resistant wheats, possessing both components of resistance. Last winter in the greenhouse, we crossed adapted wheats to F1's of VA wheats x Sumai 3 and Ning 7840. We also crossed adapted wheats to 3 recently released Purdue germplasms. F2 populations from these crosses will go to the field in the fall of 1998. As with all breeding procedures, transferring this resistance into our program will be very time consuming and require a great deal of effort.

1996-97 Studies

This past year we evaluated 22 adapted wheats for (1) resistance to initial infection and (2) resistance to spread through the head. Twenty eight Chinese wheats were also screened in study (1). In study (1), we inoculated corn kernels and spread them throughout wheat plots about 2 weeks prior to heading. The plots were mist irrigated just prior to flowering until about 1 week after flowering. This method worked very well in providing a heavy inoculum load. Pioneer Brand 2555 was used as a susceptible check planted around the plots, and it was virtually destroyed by head scab. In general, it appears that there will be significant varietal differences in response to inoculation with Fusarium. In our studies, Foster, 2510, Jackson and Coker 9803 showed some resistance or tolerance. Ernie and 2552 had a lower number of scabby florets/head, but a higher number of scabby heads.

In study 2, we inoculated single florets on 5 heads per plot with a Fusarium spore suspension, then monitored spread of the infection through the head. Again, it appears that varietal differences exist.

1997-98 Studies

We think that it is important to conduct these studies for another year to see if our results are repeatable, and to test the effect of another set of environmental conditions. We would also like to test other inoculation methods and additional genotypes.

Plan of Work

1. Approximately 30 wheat varieties and breeding lines will be planted in six row mini-plots (4' X 4') at Lexington, where the preceding crop will be corn. At about the boot stage, infected corn kernels will be spread throughout the plots and overhead irrigation will be provided during the day, through flowering. Disease incidence and severity will be assessed several times during grain fill. We will plant the same genotypes as a control in an area that will not be misted.

2. The same varieties and breeding lines will be assessed for resistance to fungal spread through the wheat and head by injecting inoculum into the central spikelets of several heads of each variety. This experiment will also be done in the field at Lexington. Disease spread will be evaluated during grain fill. We will also evaluate a method in which millet seeds are inoculated with Fusarium, then individual millet seeds will be placed in wheat florets, and disease spread will be measured. The advantage of this method is that you don't accidentally contaminate florets below the target floret when the inoculum overflows and runs down the head.

3. Thirty winter wheats from Shandong Agricultural University will be screened for resistance as described in 1 and 2. Other Chinese wheats may be obtained as well.

4. After comparing notes with other scientists this coming winter, we may evaluate other screening procedures.

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Final Report
1998

In 1997 two studies involving 22 adapted varieties and breeding lines and 30 Chinese wheats were successfully inoculated with the fungus that causes head scab, Fusarium graminearum.

Study 1

The objective of the study was to test for "Type I" resistance, i.e., resistance to initial infection. The inoculum was increased on corn kernels, then about 3 weeks prior to flowering, the infected corn was placed in the plots between the rows. Mist irrigation during flowering resulted in a very intense scab epidemic. The spreader variety, Pioneer Brand 2555 was destroyed. In short, I think we created an unrealistically heavy scab epidemic, due to our unfamiliarity with the organism, procedures, and so on.

Study 2

The objective of this study was to screen for "Type II" resistance, which is resistance to spread througout the head. This was done by injecting individual florets with Fusarium spore suspension at flowering, and then observin whether the fungus moved to other florets from the initial site of infection. The control treatment for this study was injection with distilled water.

The experiment was compromised somewhat by the background levels of scab that were observed. On the data below, the average number of scabby seeds per 10 head sample was 63 in the control treatment, vs. 116 in the injection treatment. Nonetheless, there appear to be some varietal differences: e.g. 2510 with 16% infected seeds, vs. 2568 with 54% infected seeds.

We are augmenting both of these studies with greenhouse screening this year.

1997 Scab Injection Experiment

1997 Scab Irrigation Experiment

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Final Report
1999

 In 1998 we screened a number of entries in the Uniform Eastern Scab Nursery to Fusarium head blight by inoculating field plots with the fungus Fusarium graminearum.

The best summary of this research that I can provide is the data presented at the 1998 Fusarium head blight Conference in E. Lansing, Michigan.

Tables 1 and 2 show that there is some variation among our adapted SRW wheats in resistance or tolerance to scab. We don't see anything outstanding, but we see some promising differences.

Table 3 shows the level of scab acieved in our incoulated plots, versus the background level visible in uninoulated control plots: 26 versus 16 % scabby seed. This suggests that the scab level in the inoculated plots is higher than is likely to occur with a natural infection. This means that we impose severe selection pressure, but it also means that we may discard lines that acutally show some promise under "normal" scab levels.

Future reports on this activity will be contained within the breeding project reports.

Table 1. Results of the 1998 Winter Uniform Scab Nursery at Lexington, KY.

Table 2. Evaluation of SRW Wheat Breeding Lines for Scab Resistance, Lexington, KY, 1998.

Table 3. Uniform Winter Scab Nursery Under Treated And Control Conditions, Lexington, KY, 1998.

±Inoculated with scabby corn and mist irrigated.

References

Mesterhazy, A. 1995. Types and components of resistance to Fusarium head blight of wheat. Plant Breeding 114: 377-386.

Paulitz, T.C. 1996. Diurnal release of ascospores by Gibberella zeae in inoculated wheat plots. Plant Dis. 80: 674-678.

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