Barley (Hordeum vulgare L.) is the fourth most important cereal crop worldwide. Barley production is compromised by many abiotic stresses including drought. Wild barley is a valuable source of alleles that can improve adaptation of cultivated barley to drought stress. In the present study, a nested association mapping population named HEB-25, consisting of 1420 BC1S3 lines that were developed by crossing 25 different wild barley accessions to the elite barley cultivar ‘Barke’, was evaluated under both control and drought-stressed conditions in the Australian Plant Phenomics Facility, University of Adelaide. Overall, 14 traits reflecting the performance of individual plants in each treatment were calculated from non-destructive imaging over time and destructive end-of-experiment measurements. For each trait, best linear unbiased estimators (BLUEs) were calculated and used for genome-wide association study (GWAS) analysis. Among the quantitative trait loci (QTL) identified for the 14 traits, many co-localise with known inflorescence and developmental genes. We identified a QTL on chromosome 4H where, under drought and control conditions, wild barley alleles increased biomass by 10 and 17% respectively compared to the Barke allele. Across all traits, QTL which increased phenotypic values were identified, providing a wider range of genetic diversity for the improvement of drought tolerance in barley.

This study aimed to identify wild barley alleles controlling grain size and weight with the potential to improve barley yield in Australia and worldwide. The HEB-25 nested association mapping population was used, which samples 25 different wild barley accessions in a ‘Barke’ genetic background. The HEB-25 population was evaluated in field conditions at Strathalbyn in South Australia in 2015 and 2016. Seven yield component traits reflecting ear length, grain number per ear and grain dimension were measured. Among 114 quantitative trait loci (QTL) identified for the seven traits in both years, many co-localise with known genes controlling flowering and spike morphology. There were 18 QTL hotspots associated with four loci or more, of which one at the beginning of chromosome 5H had wild alleles that increased both grain number per ear and thousand-grain weight. A wide range of effects was found for wild alleles for each trait across all QTL identified, providing a rich source of genetic diversity that barley breeders can exploit to enhance barley yield.

Since the dawn of agriculture, crop yield has always been impaired through abiotic stresses. In a field trial across five locations worldwide, we tested three abiotic stresses, nitrogen deficiency, drought and salinity, using HEB-YIELD, a selected subset of the wild barley nested association mapping population HEB-25. We show that barley flowering time genes Ppd-H1, Sdw1, Vrn-H1 and Vrn-H3 exert pleiotropic effects on plant development and grain yield. Under field conditions, these effects are strongly influenced by environmental cues like day length and temperature. For example, in Al-Karak, Jordan, the day length-sensitive wild barley allele of Ppd-H1 was associated with an increase of grain yield by up to 30% compared to the insensitive elite barley allele. The observed yield increase is accompanied by pleiotropic effects of Ppd-H1 resulting in shorter life cycle, extended grain filling period and increased grain size. Our study indicates that the adequate timing of plant development is crucial to maximize yield formation under harsh environmental conditions. We provide evidence that wild barley germplasm, introgressed into elite barley cultivars, can be utilized to improve grain yield. The presented knowledge may be transferred to related crop species like wheat and rice securing the rising global food demand for cereals.