Specific adaptation for early maturity and height stability in Icelandic spring barley

Cereal production in important growing regions is negatively influenced by climate change. This can be countered by expanding cereal production northwards in Scandinavia and Iceland, where today, barley (Hordeum vulgare L.) is primarily used as feed, as it rarely reaches malting quality. This study explores genetic factors underlying the ability of barley to mature fully in low temperature and long photoperiod. A panel of 84 spring barley lines were grown in controlled environments with different day lengths and temperatures, partially mimicking the target environment. The panel was screened for accumulated heat sum to heading, maturity, and height, all traits of importance for adaptation to the northern periphery. Subgroups with different stability and heat sum requirements were found, and day-length-neutral lines were identified. Height was temperature controlled, with lower temperature resulting in taller plants. The results were coupled to a genome-wide association study (GWAS). Despite the small panel size, the Mat-a locus was identified to have the strongest association with heat sum to heading; Ppd-H1, Mat-a, FT1, and DHAR2 with heat sum to maturity; and GA20ox1 with height. Early maturing lines with height stability have successfully been developed in Iceland, and this study confirms their performance in controlled environments for the first time. It provides insight to the mechanisms behind early maturity that will increase our ability to further adapt barley and other cereals to the northern climate. This will facilitate breeding work toward combining early maturity and height stability with traits such as quality, further enabling the northward expansion of grain production.