PROJECT RESULTS

Resistance to Wheat Midge in Durum Wheat

Applicant: 

Robert J. Lamb
Cereal Research Centre
Agriculture and Agri-Food Canada

Winnipeg, Manitoba  R3T 2M9  Canada

Table of Contents:

• Background and Objectives
• Procedure and Project Activities
• Conclusions

ARDI Project:

#98-056

Total Approved:

Date Approved:

Project Status:

Completed May, 2001

Background and Objectives:

Durum wheat is currently produced in Manitoba and sells at a substantial premium to bread wheats.  There is a real potential for value-added processing through the development of local pasta making facilities in southern Manitoba, but for this processing opportunity to be developed, a reliable supply of quality durum wheat is required.  Unfortunately, this supply may be limited by the wheat midge, which is currently the most important insect pest of wheat in Manitoba.  Female wheat midge lay their eggs on wheat heads during July, and the larvae that hatch from the eggs feed on the surface of developing seeds.  Severely damaged seeds are lost because they are too light to be retained when the crop is combined.  Less severely damaged seeds remain in harvested wheat and cause downgrading.  Durum wheat appears to suffer more damage from wheat midge than do bread wheats, possibly because the durum wheat heads remain in the susceptible pre-flowering stage longer and, therefore, receive more eggs than bread wheats. 

This proposal is part of an ongoing initiative funded by the Western Grains Research Foundation aimed at identifying new wheat midge resistant germplasm for incorporation into wheat breeding programs for western Canada.  ARDI funding will enhance the project through the following objectives:

1. Develop an efficient method for laboratory screening of large numbers of durum lines for deterrence to oviposition by wheat midge.
2. Validate in laboratory and field trials the resistance to wheat midge in lines and cultivars already identified as resistant; incorporate lines in durum breeding program.
3. Screen all currently adapted durum cultivars and advanced breeders' lines to make recommendations which would provide the highest level of resistance to wheat midge for Manitoba durum producers.

This research should improve the returns of durum producers in Manitoba and, thereby, enhance the reliability of durum production and prospects for value-added durum processing in Manitoba.

Procedure and Project Activities:

1st 6 Months of the Project:

The initial step in the study was to screen 40 of the most promising durum wheat lines in field plots at 3 locations in Manitoba in 1998.  Each plot was carefully monitored for growth stage.  Wheat heads naturally exposed to wheat midge at the appropriate stage were collected from the plots when oviposition was complete.  Another sample of heads was collected two weeks later when larvae would have completed development and damaged the seed.  Each head was dissected to determine the number and distribution of eggs on each spikelet of each head, and later sampled heads were dissected to determine the number of larvae infesting each head.  This data was analyzed and revealed that wheat midge lay their eggs in different places on different lines.  A few lines were confirmed to have very few eggs or larvae compared with other lines.  The field tests were used to identify 6 durum lines for further laboratory testing.  One of these is Avonlea, a recently developed cultivar which is susceptible and will serve as a control.  Another is a super-susceptible line which will also serve as a control.  The remaining 4 lines had egg and larval numbers about 1/20th of that observed on Avonlea.

These 6 lines have been tested in the laboratory to develop efficient screening methodologies and to confirm the resistance.  The tests to date confirm that the 4 potentially resistant lines also receive few eggs in the laboratory.  Because durum wheats vary substantially in height, laboratory screening proved more difficult than for bread wheats.  Therefore, we tested a new method using excised heads in florist water picks.  Excised heads received as many eggs as intact heads and so this method is being developed into a rapid and more efficient method for screening durum for oviposition deterrence in the laboratory.  The most promising lines have now been crossed with advanced durum breeding lines in cooperation with Dr. Julian Thomas, Geneticist, and Dr. John Clarke, Durum Breeder, Agriculture and Agri-Food Canada. 

2nd 6 Months of the Project:

Laboratory trials were expanded to include no-choice as well as choice tests.  These trials confirmed that 2 lines of durum wheat show oviposition deterrence, reducing oviposition by 70­-75%.  Morphological characters of the heads of 40 durum wheat were quantified and associated with the level of oviposition deterrence.  Our hope was that the resistant wheats could be identified on a morphological basis which would speed the selection for resistance in field trials.  This aspect of the work proved very time consuming but a successful outcome would have been well worth the trouble.  Unfortunately, no morphological traits were found that explained the resistance and could be used as a marker.  This work did, however, confirm the reliability of the egg counting methods we have developed.  In the spring of 1999, the most promising durum lines and some additional accessions were selected and seeded in the field for the final round of field validation of this type of resistance.  We were unable to seed and subsequently screen the breeding lines made by crossing the resistant line with an adapted durum, because the doubled haploid seeds were not ready in time to go into the field.

3rd 6 Months of the Project:

The resistance proved to be stable over time during the field season and at low and high infestation rates in the field.  The resistance was also found to occur in a multi-row plot as well as in single-row plots, and oviposition was reduced to the same extent in the large plot as in the laboratory.  We are now confident that the oviposition deterrence represents a reliable source of resistance to wheat midge for use in durum wheat.  The new lines that were screened all proved susceptible and received as many eggs as a typical susceptible line.  This result confirms that oviposition deterrence is uncommon in durum wheat accessions (2 lines out of more than 300).  Therefore we will proceed to exploit the resistance source we have already detected, rather than expending a great deal of effort looking for additional sources.  Variation in the oviposition rate among lines was not associated with variation in the rate of development between the onset of heading and anthesis.  This result is useful because it shows that we can screen more efficiently by not being so careful about achieving precise synchrony in wheat development.

4th 6 Months of the Project:

A publication on oviposition deterrence in durum wheat was prepared.  In addition, a publication was prepared on methods for screening for oviposition in durum and in common wheat. Lines with oviposition deterrence have now been incorporated in the breeding program for durum wheat.

Conclusions:

1. An efficient method for laboratory screening was developed using excised spikes in cages with laboratory-reared wheat midge.  
2. A single old cultivar named `Kahla' was confirmed as reducing egg-laying by 70% in comparison to commercial durum wheats.  This wheat has been crossed into an adapted cultivar for western Canada, and incorporated in the durum wheat breeding program.
3. Cultivars and advanced breeders' lines were screened, but all proved to be completely susceptible to wheat midge.  Therefore, no recommendation on the least susceptible cultivar can be made.  Rapid progress is being made in developing a resistant line through the durum breeding program of Agriculture and Agri-Food Canada, using both the egg-laying deterrence developed as part of this project, and another resistance mechanism transferred from common wheat.

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