Seed development in field-grown orchardgrass

Little is known about seed development and its contribution to seed yield components in orchardgrass (Dactylis glomerata L.). Field trials were conducted in 2018 and 2019 to investigate orchardgrass seed development and the effects of four trinexapac-ethyl (TE) plant growth regulator and spring nitrogen (N) treatments on this process: untreated control, TE (210 g ai ha⁻¹), spring N (112 kg ha⁻¹), and TE + N. Regression analyses were used to elucidate seed development in three spikelet positions. In 2018, seed weight increased over growing degree days (GDD) in a bi-phasic segmented pattern in seed from distal and central spikelets but increases were linear from proximal spikelets. In 2019, seed weight increased in proximal spikelets following a bi-phasic segmented function, while seed weight increase in central spikelets was also bi-phasic, except for the TE treatment. Seed growth rate varied among spikelet positions, ranging from 0.22 to 0.34 mg GDD⁻¹ per 100 seeds. The seed growth rate varied among TE and N treatments, ranging from 0.31 to 0.47 mg GDD⁻¹ per 100 seeds. The TE + N treatment had the shortest seed filling duration and one of the smallest seed growth rate values, producing low seed weight. The TE + N treatment produced high seed number and yield, indicating a reduction in seed abortion or shattering. Seed carbon (C) and nitrogen (N) content increased during seed development and peak deposition preceded physiological maturity. No effects of TE on deposition of C or N in orchardgrass seed occurred.