Screening Cultivars for Disease Resistance

Wheat and barley are important commodities in Minnesota’s agricultural economy. Unfortunately, diseases cause significant reductions in both the yield and quality of these crops each year.  Epidemics of Fusarium head blight (FHB or scab) on wheat and barley crops since 1993 have wreaked havoc on small grains production in the Upper Midwest. In addition to FHB, other foliar diseases of wheat and barley have also severely reduced yields, although their impact has been dwarfed by FHB.

The use of resistant cultivars is the best, cheapest and most environmentally firendly, means for controlling plant diseases.  To this end the faculty, staff and students of the Small Grains Pathology Laboratory on the St. Paul campus of the University of Minnesota have partnered with the wheat and barley breeding programs in the development of new cultivars with improved resistance to diseases.

Reliable and effective field and greenhouse screening of breeding lines for FHB and the foliar diseases such as tan spot of wheat and net blotch of barley are critical to the success of the university’s plant breeding programs. The breeding efforts aimed at improving FHB resistance has led to the introduction of new germplasm into the breeding program. While this was essential to improve the FHB resistance, susceptibility to other diseases - previously controlled effectively through resistance (e.g. leaf rust and stem rust) has increased with the addition of this new material.  To ensure that cultivars susceptible to any of the common diseases in Minnesota are not inadvertently released for commercial production, it is essential that all advanced breeding lines be rigorously screened for resistance to all the major diseases that occur in our region. For this reason, field and greenhouse evaluation of advanced breeding lines from the wheat and barley improvement programs for resistance to the major foliar diseases is an ongoing activity for the small grains pathology team in Dr Ruth Dill-Macky’s laboratory.

Have you ever wondered where these scientists get the pathogens they work with? It may well be from your production field. Each summer the folks from the Small Grains Pathology Laboratory spend time surveying Minnesota’s wheat and barley crops, looking for diseased plants and sampling these plants to collect the pathogens that cause disease. Back in St. Paul the scientists then can isolate the pathogens, grow them in pure culture and put them into storage for future use.  These pathogen collections to provide the source of inoculum used to generate the disease again in the screening nurseries that help identify new resistant lines developed by the plant breeding programs.

In 2007 screening for resistance to FHB was conducted at three Minnesota locations; St. Paul, Morris and Crookston. As much as 400 liters of inoculum of the pathogen (fungal spores suspended in water) was used to inoculate these nurseries. At all locations mist-irrigation systems were established to provide the environmental conditions suitable for disease development. The pathology group then assisted the breeding programs in evaluating the material once the disease has developed.  Pathology personnel also assisted in the greenhouse evaluation of lines for their reaction to FHB. The identification of resistant material has enabled the breeding programs to make significant progress in breeding for FHB resistance.

In addition to FHB work with other diseases is also ongoing. In 2007, a field nursery was established in St. Paul to screen wheat lines for their reaction to tan spot.  This nursery evaluated 420 rows of wheat, encompassing advanced and preliminary lines from Dr. Jim Anderson’s wheat breeding program.

Dr. Jason Scott, Research Associate (left), Janne Kvamme, summer intern from the University of Life Sciences, Norway (center) and Dr. Ruth Dill-Macky, Associate Professor (right) collecting heads of Fusarium-infected wheat from commercial fields in the Red River Valley. They will use these heads to obtain new isolates of the pathogen to be used to test the reaction of new wheat and barley lines to Fusarium head blight.

Approximately 1,000 barley entries were tested as seedlings for their reaction to the net blotch pathogen. This seedling screening is conducted in the greenhouses on the St. Paul campus.  Approximately 40% of the lines tested exhibited resistance and were advanced in Dr. Kevin Smith’s barley breeding program.  A field screening nursery was also established at Stephen to screen additional barley lines for their reaction to net blotch.

This important work facilitates the development of new wheat and barley cultivars with multiple disease resistance and will ultimately increase the sustainability of the production of small grains in Minnesota.

Beheshteh Zargaran, Junior Scientist, preparing cultures of the fungal pathogen that causes net blotch of barley for storage in the Small Grains Pathology laboratory in St. Paul.

-- Dr. Ruth Dill-Macky, plant pathologist, University of Minnesota.