Late-heading parental selection in orchardgrass (Dactylis glomerata L.)

Dactylis glomerata L., orchardgrass or cocksfoot, is frequently planted as a companion crop in perennial forage legumes such as alfalfa (Medicago sativa L.). However, many commercial orchardgrass cultivars flower earlier than legumes, resulting in a reduction in grass yield and nutritional value if harvested to maximize the legume. Additionally, during orchardgrass seed production over years, later flowering can gradually shift to earlier flowering. In this study, we employed parental selection based on half-sib family (HS-family) trait values for dry matter yield (DMY) and heading date (HD), and augmented it with marker-assisted selection to enrich for late-heading-associated alleles in six vernalization and flowering time candidate genes. The parent population resulted from polycrossing three late-heading orchardgrass germplasm sources and evaluating 94 HS-families. HDs differed by years and locations for both the parent and HS-family populations. Of the 313 single-nucleotide polymorphisms (SNPs) identified within the candidate genes, 16 were associated with HD with a range of effects from 0.48 to 3.37 days to heading. An SNP detected across multiple years and locations in this study was also found in a previous study, within the intron of the Constans 1 gene (DgCO1). DMY was not highly significant in this study, highlighting a large environmental effect alongside lower variation across the HS-families. However, parental plants fixed for the SNP within DgCO1 showed a trend to later heading as well as higher DMY.