Exploring traditional and novel spike traits associated with seed retention in perennial ryegrass by integrating 2D and 3D image analysis

Seed shattering is a major economic problem in seed production of perennial ryegrass (Lolium perenne L.). The objective was to identify potential relationships between phenotypic traits and seed retention in a 2-year field trial with 21 diverse global accessions of perennial ryegrass. Accessions were grouped according to level of seed retention. Phenotypic traits examined were growth habit, spike length, curvature of the spike, spikelets per spike, spikelet length, internode length between spikelets, angle of spikelet insertion into the rachis, seeds per spike, and seed weight. Traits were captured and measured by use of novel two-dimensional (2D) and three-dimensional (3D) imaging tools. Among accessions, median seed retention values for the high and low seed retention groups were 61% and 36%, respectively. Four traits were found to significantly impact seed shattering: spike length (p ≤ 0.01), seed weight (p ≤ 0.001), seeds per spike (p ≤ 0.05), and internode length between spikelets (p ≤ 0.01). Seed retention was highest in accessions with short spikes. Most of the accessions that had high seed retention also had lower mean seed weight than the commercial plant materials. Accession (PI 231620) had both high levels of seed retention and a mean seed weight that is acceptable in the marketplace. These qualities may be used to improve seed retention in the breeding of perennial ryegrass cultivars. The 2D and 3D imaging methods have applicability in measurement of other plant morphological traits and across a broad range of plant species.