| Summary: | Barley is the most grown cereal in the Nordic countries, and the fourth most important cereal crop globally. Its use is mainly for feed, but a large portion is also used by the brewing industry. At northern latitudes, such as Iceland, the barley production goes almost exclusively to feed. There is a potential for a diversification of the end-use, but this is dependent on the quality of the produce. The ability of spring barley to mature in cold temperature is of agronomic importance for cultivation in Iceland. Summer temperature in Iceland is on average lower than at comparable latitudes which often makes it impossible for barley to reach full maturity. This negatively impacts grain quality, and necessitates grain drying before storage, which adds considerable cost for the producer. In this study, Icelandic early genotypes were grown alongside a panel comprising the current Nordic barley gene pool in multi-location field trials and genome wide association studies (GWAS) were used to elucidate loci of importance for heat sum to heading, heat sum to maturity, and straw length. Nordic barley was studied in controlled environments of contrasting day length and temperature conditions to elucidate the effect on heading, maturity, and straw length. GWAS was used to find marker trait associations. A panel of genotypes were selected for an in-depth study of allelic diversity in the four earliness genes Ppd-H1, HvELF3, HvCEN, and HvFT1. An allele combination from the three most significant marker-trait associations (MTAs) had a 214°dC lower heat sum requirement to maturity, corresponding to 30 days in Iceland. Several loci of adaptive importance in Icelandic conditions were found, including HvELF3, HvGA20ox2, and HvGA20ox1. The winter allele of Ppd-H1, in combination with a HvFT1 allele, caused extreme earliness in Icelandic spring barley, however with a severe yield penalty. The winter-type allele of HvCEN was unique among a set of Icelandic and Finnish genotypes with the ability to combine earliness with high yield. ...
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