Nye veier mot forbedring av flatskurvresistens i norske poteter

The main objective of this project is to develop and implement new molecular tools and identify genetic resources for effective potato breeding against common scab disease. In order to achieve this goal, and in the last four years we have been focusing on (i) developing rating scale to classify the severity of common scab infection on potato (incl. scab lesion % and depth of lesion); (ii) assessing current Norwegian and AGRICO (Dutch) potato core variety collections for common scab resistance; (iii) developing plant populations that are suitable for genetic studies of the common scab resistance that have similar background, but differ in their resistance to common scab disease; (iv) genotyping the Norwegian and AGRICO (Dutch) potato variety core collections; (v) Identify of genetic markers linked to the potato common scab resistance by joint analyses of genetic and phenotypic data; (vi) performed interaction between the potato plant and common scab causing pathogen. To achieve our main goal to identify molecular markers that are linked to common scab disease on potato, it is crucial to obtain potato varieties and segregated populations that contain similar genetic background material but differ in their ability to withstand common scab disease. Assessing current potato core variety collections (Graminor and AGRICO) for common scab resistance is important step for genetic marker development and identification of novel genes linked to the potato common scab resistance (WP3). Segregated populations will be used to validate the usage of the developed molecular markers in plant breeding. Graminor potato core varieties (206 varieties) were visually scored for 3 years (2014, 2015, 2016) in common scab field (Bjørke, Hamar). The results were collected and used further for genomic studies in WP3. Further greenhouse (pot tests) were also performed in 2014, 2015 and 2016 to evaluate common scab more precisely in one tetraploid (cultivated potato) population (GACs11.12.099) and diploid population (GAD12.13.002). These populations have shown promising results to be used in molecular markers validation. AGRICO potato core collection (300 varieties) and several populations were evaluated on the common scab field. Unfortunately, in 2016, common scab symptoms were hardly developed due to unfavorable weather conditions. Further testing will be done in 2017. In the greenhouse, a pot trial with 20 different varieties was performed. This was a repeat of the experiment in 2015. Tubers were harvested, scored and data analysis will follow soon. In 2015, 20 different wild Solanum species were analysed in a pot trial. After harvest, genotypes without scab symptoms were selected. These selected genotypes were planted in 2016 in common scab infected soil and grown under short day conditions. Tubers were visually scored for common scab symptoms and about half of the genotypes was discarded due to the presence of common scab symptoms. Around 60 genotypes have left and these will be tested again in 2017. Phenotype field data from Agrico (2013, 2014, and 2015) and Graminor (2014, 2015, and 2016) were analyzed to obtain symptom averages in 351 tetraploid potato varieties. These averages were used as input in the association (DNA and phenotype) analyses. Previously, we have obtained genomic (GBS) data from the Institute for Genomic Diversity, NY, USA. However, resolving these data into a format that proved useful for association analyses proved to be challenging. We initially treated the autotetraploid potato as a diploid and did association analyses using the GAPIT software, but this was not an adequate solution. With our own in-house scripts built around the fitTetra R package, we resolved the biallelic genotypes into the five possible plex levels (AAAA, AAAa, etc.), retaining 9770 markers for the 351 potato lines. The association analysis was then completed and a few markers indicated significant associations. For now, association analyses have identified 4 markers from the Graminor panel and 24 markers from the Agrico panel that are linked to common scab resistance. These potential markers will be further tested in independent segregated populations before applying in breeding. In this project, we have also obtained detailed knowledge about potato genes involved in the infection process to better understand the mechanism associated with resistance to potato common scab. This work has been completed and recently published in Molecular Plant Pathology (Dees et al. 2015; doi: 10.1111/mpp.12323).

Potet er den nest viktigste kulturveksten i Norge og den fjerde viktigste i verden. Flatskurv er en kvalitetssykdom på potet som forårsakes av noen få av mange arter i den jordboende bakterieslekten Streptomyces. Skurvsårene gir synlig kvalitetsforringels e og gjør i tillegg knollene mer utsatt for uttørking. Dette er således en viktig sykdom både for produsenter, omsetningsapparat og konsumenter. Det finnes ingen tilfredsstillende kjemiske metoder for bekjempelse av sykdommen. Det finnes heller ikke fulls tendig resistens i kjente potetsorter, men det faktum at noen sorter er relativt robuste mot flatskurv tyder på at sykdommen kan bekjempes gjennom målrettet avl. En viktig målsetning for Graminor og det norske potetforedlingsprogrammet er derfor å utvikle nye sorter som har bedre eller helst fullstendig resistens mot flatskurv. Dette vil være et viktig ledd i å forbedre økonomisk utbytte fra potetavlinger. Hovedfokus i prosjektet er å effektivisere foredlingsprosessen i potet for utvikling av sykdomsresis tente sorter gjennom etablering av molekylære markørteknikker. Første utfordring er å identifisere plantemateriale som divergerer med hensyn på sykdomsresistens. Som en del av dette arbeidet vil vi teste ut forskjellige metoder for effektiv resistensscree ning (fenotyping). Videre vil vi identifisere molekylære markører som kan brukes for å identifisere flatskurvresistente sorter på et tidlig stadium i foredlingsprosessen. For fremtidig bekjempelse av flatskurv er det også viktig å få en dypere forståelse av hvilke faktorer som påvirker utviklingen av skurvangrep, og hvilke gener som er involvert i infeksjon og sykdomsutvikling hos både planta og bakterien. En liten del av prosjektet vil derfor gå til slik grunnleggende strategisk forskning. Prosjektet tot alt vil bidra til å forbedre vår forståelse av en kompleks egenskap som resistens samtidig som det vil utvikles verktøy og plantemateriale for foredling av nye flatskurvresistente potetsorter.