Variability of agronomic and quality traits of winter hull-less barley from the European collection

Hull-less barley (Hordeum vulgare L. var. nudum) is an underutilized form of barley that shows significant potential for broader use in human nutrition due to its exceptional nutritional value and beneficial health effects. This potential was the basis for research within the CROPDIVA project, funded by the Horizon Europe program. Despite its historical importance as a staple food, it currently occupies less than 2% of the total barley production area in Europe. The important agronomic, morphological and grain quality traits were investigated in order to determine their value for agriculture and the food industry. The study included 72 genotypes of winter hull-less barley obtained from the IPK genebank in Gatersleben (Germany), along with two control cultivars sown in 10 replications. The experiments were established during the 2023/24 and 2024/25 at the Rimski šančevi experimental station of the Institute of Field and Vegetable Crops in Novi Sad using an augmented block design. This research focused on assessing phenotypic variation of following characteristics: biomass, thousand grain weight, harvest index, grain color, threshability, test weight and grain protein content. Among the tested genotypes, 67 belong to the six-rowed (6R) type, and 7 genotypes are two-rowed (2R) types. After harvest, the protein content of the seeds was determined by the combustion method according to the DUMAS procedure (AOAC 992.23, 1998). Data analysis employed BLUEs (Best Linear Unbiased Estimators) to correct for spatial variation across the 10 blocks. Descriptive statistics revealed substantial phenotypic variability with the highest coefficients of variation (CV) observed for biomass (27.8%) and thousand-grain weight (27.5%). Conversely, hectoliter mass remained highly stable (CV = 4.2%). Two-rowed genotypes achieved a statistically significantly higher biomass (2,445 g m- ²) and thousand grain weight (49.1 g) compared to six-rowed barley, where the biomass was 1,614 g m- ², and thousand grain weight was 30.0 g. In contrast, the average values of hectoliter mass in six-rowed forms (84.6 kg hL-1) and protein content (12.3%) were higher compared to two-rowed forms (79.2 kg hL-1; 10.3%). Only seven genotypes showed a lower degree of threshability, with some seeds retaining hulls after mechanical dehulling. Aleurone layer analysis identified a predominance of white color, while light blue, dark blue, purple, and black pigments were less frequent. Correlation analysis showed that the most pronounced positive correlation was found between biomass and thousand grain weight (0.56). A modarate correlation was detected between TGW and hectoliter weight (-0.47). Principal component analysis (PCA) confirmed a high degree of phenotypic variability explaining 63.3% of the total phenotypic variability indicating mutual independence of traits related to protein content and yield components. These results confirm that the European collection of hull-less barley represents a valuable genetic resource suitable for use in breeding programs and improvement of cultivars intended for human consumption.