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

Authors: GETZ, MEGAN - Utah State University; Robbins, Matthew; Thorsted, Kimberly; Jensen, Kevin; Robins, Joseph; CREECH, EARL - Utah State University; Bushman, Shaun

Submitted to: Crop Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/9/2024
Publication Date: 2/15/2024
Citation: Getz, M., Robbins, M.D., Thorsted, K., Jensen, K.B., Robins, J.G., Creech, E., Bushman, B.S. 2024. Late heading parental selection in orchardgrass (Dactylis glomerata L.). Crop Science. 64(2):1072-1082. https://doi.org/10.1002/csc2.21200.
DOI: https://doi.org/10.1002/csc2.21200

Interpretive Summary: Orchardgrass 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. We conducted a cycle of recurrent selection for dry matter yield and heading date, 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. Of the 313 molecular markers within the candidate genes that varied, 16 were associated with heading date. In particular, a SNP markder detected across multiple years and locations in this study was also found in a previous study, within the intron of the Constans 1 gene. Dry matter yield 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 marker in DgCO1 showed a trend to later heading as well as higher dry matter yield.

Technical Abstract: 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, 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. Heading dates differed by years and locations for both the parent and HS-family populations. Of the 313 SNPs identified within the candidate genes, 16 were associated with heading date with a range of effects from 0.48 to 3.37 days to heading. A 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). Dry matter yield 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 dry matter yield.