WP1 - Pathogen populations:
The establishment of reference isolate collections of both Parastagonspora nodorum (causal agent of leaf blotch in wheat) and Drechslera teres (causal agent of net blotch in barley) was completed in early 2015. A total of 428 P. nodorum isolates and 404 D. teres isolates have been collected and stored as dried plugs at -80C at NIBIO Plant health.
About 150 P. nodorum isolates have been characterized for mating type, and a subset of 65 have been screened for the presence of known effector genes. Results show that Norwegian isolates of P. nodorum produce ToxA, Tox2 and Tox3. The frequency of ToxA is much higher than previously characterized European populations of this pathogen, which indicates that the presence of this effector might give the locally adapted pathogen population a selective advantage on the wheat cultivars grown in Norway.
The entire collection of 404 D. teres single spore isolates was ddRAD (Double Digest Restriction Associated DNA) genotyped on the Ion Torrent Platform during the autumn of 2015. Data analysis to assess the genetic diversity and population structure of the pathogen was completed during spring 2017. The results show that the Norwegian population of D. teres has a high level of genetic diversity, frequently undergoes sexual recombination and has a high ability to adapt and evolve virulence to resistance genes in the barley cultivars that are grown by farmers.
WP2 - Tools for resistance breeding:
Field testing of large collections of wheat and barley cultivars and relevant mapping populations was conducted in 2013, 2014, 2015 and 2016 to obtain data for genetic studies. The four seasons were very different in terms of weather and natural conditions for disease development. However, we still got good data from our field trials in all years due to established methodology with inoculation of infected straw in combination with mist irrigation to create favorable conditions for leaf blotch diseases. Seedling inoculations have been conducted in the greenhouse for both pathogens and most of this work was finished by spring 2016.
For leaf blotch resistance in wheat, we have updated the linkage maps of the SHA3/CBRD x Naxos population with SNP markers from the Illumina 90K wheat chip. Based on four years of field data, inoculation and infiltration with single isolates at the seedling stage as well as testing for effector-sensitivity we revealed that a big proportion of the variation in field resistance could be explained by Tox3 sensitivity. This is the first time that the Snn3/Tox3 interaction has been shown to be important for adult plant resistance under natural infection in the field, and the results were published in early 2017.
An association mapping panel of Norwegian spring wheat (MASBASIS) has also been genotyped with the same 90K chip, tested in field trials and in inoculation and infiltration experiments at the seedling stage. Field data shows that the Zebra, Mirakel, Demonstrant and Krabat are among the most resistant of the current spring wheat cultivars while Bjarne and Seniorita are the most susceptible. The work shows that sensitivity to ToxA and Tox3 is common in Norwegian spring wheat, and that sensitivity to these effectors results in increased susceptibility in the field. A manuscript describing this was submitted in spring 2017. The association mapping on the same material was also completed, and is almost ready for submission. The project has also provided leaf blotch resistance data on several other mapping populations, which will be used in future projects.
In barley, the BYGGBASIS panel and the Arve x Lavrans population were genotyped with a 9K SNP chip from Illumina, and tested in field trials over four and three years, respectively. The testing has shown that Tiril, Tyra and Iver are among the most susceptible of the current barley cultivars while Marigold and Fairytale are the most resistant. The QTL mapping in Arve x Lavrans based on field data and seedling inoculations has been completed and identified four important QTL on 4H, 5H, 6H and 7H. Association mapping based on BYGGBASIS showed that net blotch resistance in the Norwegian barley breeding program is based on many genes with small to moderate effects, and that many genes need to be combined in order to achieve sufficient level of field resistance. Both studies were in 2017 published in renowned international journals.
For both diseases, we have identified closely linked SNP markers to the most promising QTL, and these were validated on the KASP genotyping platforms at NMBU and Graminor during spring 2017.
The government has an ambitious goal to increase the Norwegian food production with 20% by 2030, and increasing the yields of wheat and barley will be crucial in order to achieve this. Locally adapted cultivars that can maintain yield and quality under th e prevailing climatic conditions and production environments are needed. Recent years have been challenging due to serious problems with leaf blotch diseases like Stagonospora nodorum blotch (SNB) in wheat and net blotch in barley resulting in grain shriv elling and reduction in yields.
Progress from resistance breeding has been slow and the genetics of resistance in Norwegian wheat and barley is poorly understood. The recent discovery of necrotrophic effectors (NEs) produced by leaf blotch pathogens and their role in host susceptibility has revolutionized the understanding of host-pathogen interactions and is enabling more effective resistance breeding. This project will link Graminor and the research groups at UMB and Bioforsk with the world's leading e xpertise on leaf blotch diseases in cereals. It will develop the necessary tools to breed high-yielding wheat and barley cultivars with improved resistance by utilizing molecular marker data and national competence built up through the wheat genome sequen cing project. Along with this, the project will build up necessary plant pathology competence at Graminor through the training of a PhD student that will work closely with the breeding programs.
The project is organized in two work packages with WP1 focu sing on characterization of the Norwegian pathogen populations and determination of the roles of NEs in host susceptibility. WP2 will utilize this information to develop tools for identification and elimination of host sensitivity alleles. Important deliv erables to the Graminor wheat and barley breeding programs are improved testing methodology, in-depth knowledge about resistance and NE sensitivity in the Norwegian wheat and barley and validated marker assays.