Stipendiatstilling 2 NIBIO (2021-2024)

Title:Molecular breeding for pathogen resistance in strawberry The garden strawberry, Fragaria × ananassa, is a highly popular and economically important berry crop cultivated in various climates worldwide. It first occurred during the 1700s in western Europe as the result of accidental hybridization between the South American F. chiloensis and the North American F. virginiana. These two species are adapted to vastly different growing conditions and made F. × ananassa a genetically diverse crop. Desirable complementary traits derived from the parent species have enabled the selection and domestication of F. × ananassa over 300 years breeding history. Improved strawberry cultivars have historically been obtained through traditional crossbreeding, where the most desirable offspring from crosses of superior individuals are selected based on phenotypic evaluations. This process has been relatively slow, but intensive selection significantly increased fruit size and yield. Recently established F. × ananassa genomes and genotyping arrays have enabled molecular breeding tools that can make strawberry breeding more efficient. Maintaining genetic diversity is essential for ensuring successful breeding and long-term adaptability to emerging challenges. However, neglect of disease resistance breeding, due to reliance on chemical treatments, has led to reduced resistance among current strawberry cultivars. Given the decrease in genetic diversity within breeding populations, there is an urgent need to find new sources of resistance and other important traits. To address this issue, a population genetics analysis of domesticated and wild Fragaria species was performed. There was a distinct genetic difference between F. × ananassa and its wild relatives. Cultivars clustered into five groups that reflected breeding history, with old European cultivars and new Californian cultivars being the most genetically separated. Despite this, a noticeable preference for Californian cultivars in recent European breeding was observed. Genetic pedigree analyses revealed that many cultivars were true-to-type and have been preserved for decades. Several other cultivars were identified as not true-to-type, including some cultivars that may be lost forever. Taxonomic classifications at the species and subspecies level were confirmed, but discrepancies between the assigned taxa and the genetic patterns were identified for some accessions. The population genetic analysis revealed several distinct groups that may harbor valuable genetic variation. Powdery mildew, caused by the fungus Podosphaera aphanis, is a common disease that many strawberry cultivars are highly susceptible to. Genetic analysis of powdery mildew resistance in a Nordic strawberry breeding population revealed substantial variation between accessions. Genomic selection was evaluated for its potential to improve selection processes. A prediction accuracy of 40% was achieved when genomic selection was used to predict the powdery mildew resistance of a testing population that differed from the training population. The ability of strawberry cultivars to resist powdery mildew infections can be influenced by genetic variation within P. aphanis populations. Powdery mildew samples from various regions of Norway were thus analyzed to identify potential genetic variation. The genetic analysis showed that there are at least two genetically distinct P. aphanis groups in Norway. Genetic differences between the groups could not be explained by geographic separation, although samples from one group originated from a specific location. This research project shows that there are several genetically unique strawberry groups with potential beneficial traits, that powdery mildew resistance can be improved through genomic selection, and that at least two genetically distinct strawberry powdery mildew groups exist.

Å opprettholde genetisk mangfold er avgjørende for å sikre vellykket foredling og langsiktig tilpasning til nye utfordringer. Utelatelse av sykdomsresistensforedling, på grunn av god tilgang på plantevernmidler, har imidlertid ført til redusert resistens blant dagens jordbærsorter. Som følge av redusert genetisk mangfold i foredlingspopulasjoner, er det et akutt behov for å finne nye kilder til resistens og andre viktige egenskaper. Resultatene våre viser at det fortsatt er mye genetisk variasjon hos jordbærsorter som kan nyttes i foredlingsarbeidet for å få mer resistente planter fremover. Genetiske slektskapsanalyser viste at mange sorter var sortsekte og har blitt bevart i flere tiår. Flere andre sorter ble identifisert som ikke sortsekte, inkludert noen sorter som kan være tapt for alltid. Vi viser at genomiske metoder kan brukes til å finne ut om sorter i genbankene er korrekte, duplikater eller feilmerket. Det å kunne vite at man faktisk jobber med korrekt sort er veldig viktig for det fremtidige foredlingsarbeidet for å få frem nye norske sorter.