Reith, Francis Arthur2024-10-292024-10-292024-10-28vt_gsexam:41518https://hdl.handle.net/10919/121505Cultivated barley typically exhibits either a winter growth habit or a spring growth habit. Some cultivars display a facultative growth habit, allowing them to be cultivated as either winter or spring crops. This study evaluated 1,128 elite barley cultivars and breeding lines under fall and spring sowing to determine which lines had a facultative growth habit and the underlying genetics thereof. In the fall of 2021 and subsequent spring of 2022, The first trial focused on identifying genetic factors associated with facultative habit. Results indicated that facultative lines were rare, with the majority exhibiting a winter growth habit. GENOME WIDE SCANS revealed no novel QTL associated with facultative habit, but significant QTLs on chromosome 4H were identified, correlating with the vernalization gene "VRN-H2." Several haplotypes found on chromosome 4H within appear significant and may contribute to differences in facultative habit. Only 28% of facultative lines could be accurately predicted based on genetic data, suggesting that facultative habit is a more complex trait than previously understood. Significant epistatic interactions between chromosome 4H and 4 other chromosomes were discovered. These findings indicate facultative habit is a much more quantitative trait than previously reported. The second trial involved growing the best-performing lines from the first trial under both fall and spring sowing conditions. Winter-sown barley consistently outperformed spring-sown barley in grain yield across all facultative lines. Despite strong performance under spring conditions, yield rankings were inconsistent across both sowing seasons, implying that agronomic performance cannot be reliably predicted across seasons. Notably, the Virginia Tech malt barley line 'Avalon' demonstrated facultative growth but exhibited poor agronomic quality under spring sowing. In contrast, lines such as 'VA22M-20DH1349' and 'VA22M-20DH1182' showed superior performance in both sowing regimes, indicating their potential for future breeding programs and agronomic trials for facultative barley in the American East.ETDenCreative Commons Attribution-NonCommercial 4.0 InternationalBarleyThesis