Developing Low-GN and GN-zero Winter Malt Barley for the Eastern United States

Abstract

Glycosidic nitriles (GN) are carcinogenic precursors produced by barley as a natural defense against insects. The most common GN in barley, epiheterodendrin (EPH), contains a cyanide group that, when combined with heat and copper during distillation, forms ethyl carbamate (EC), a known carcinogen. While GN-zero barley varieties have been developed in the European Union and the western United States, no known GN-zero or low-GN varieties are currently adapted to the Eastern U.S. climate. The Virginia Tech Small Grains Breeding and Genetics Program, in collaboration with the Center for Craft Food and Beverage at Hartwick College, is leading a multi-pronged effort to develop GN-zero winter malting barley adapted to the Eastern U.S. In 2023, grain from 220 elite malt breeding lines and two known GN-zero checks were grown in Blacksburg, VA and screened for GN content using a colorimetric assay. All VT lines tested positive for presence, and 93 were sampled for micromalting and GN quantification 2023. These lines, along with controls, were genotyped using genotyping-by-sequencing (GBS) and evaluated for genomic predictability and selection potential for GN reduction. Despite a low heritability estimate (h2 = 0.24), bi-directional genomic selection was effective (p = 0.003). Repeatability was confirmed through a second phenotyping round in fall 2024, where 48 lines showed strong GN correlation between years (r = 0.72), supporting the feasibility of breeding a GN-zero variety. In parallel, a winter speed breeding protocol was implemented to accelerate generation advancement and enable earlier GN screening in segregating populations. Of the 2,520 seeds planted from 12 GNzero crossed with adapted breeding lines F2:3 families, 103 heads were successfully harvested under extended photoperiod and controlled temperature conditions. These families will be advanced and evaluated under field conditions in Blacksburg, VA, laying the groundwork for future variety release. Together, these efforts demonstrate the viability of integrating phenotypic screening, genomic selection, and rapid generation cycling to breed low- and zero-GN barley adapted to the Eastern U.S.