Graduate Thesis Or Dissertation
 

Seed Development in Orchardgrass (Dactylis glomerata L.) in Relation to Plant Growth Regulators and Spring Nitrogen

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  • Orchardgrass (Dactylis glomerata L.) is an important seed crop, but unlike other cool-season perennial grass seed crops such as perennial ryegrass (Lolium perenne L.) and tall fescue [Schedonorus arundinaceus (Schreb.) Dumort.], seed yields have not increased over time so there is considerable room for improvement. Research suggests that plant growth regulators (PGRs) such as trinexapac-ethyl (TE), chlormequat chloride (CCC), and spring nitrogen (N) application have been found to increase seed yield in orchardgrass through its effect on increasing seed number. Field trials were conducted at Hyslop Experimental Farm near Corvallis, OR in three crop years (2016-2017, 2017-2018, and 2018-2019) to examine the effects of spring N and PGRs on seed production characteristics in orchardgrass. Spring N was applied at four rates: 0, 112, 157, and 202 kg N ha-1 and PGR applications were timed using the BBCH [Biologische Bundesanstalt, Bundessortenamt und Chemische Industrie] scale. The four PGR treatments consisted of : 0 g ai ha-1, 210 g ai ha-1 TE applied at BBCH 32, 210 g ai ha-1 TE applied at BBCH 51, and a combination of 105 g ai ha-1 TE + 1500 g ai ha-1 CCC applied at BBCH 32. Four treatments were used to examine seed development, and carbon and nitrogen deposition in orchardgrass: control, TE (210 g ai ha-1), N (spring N applied at 112 kg ha-1), and TE + N. Regression analyses were used to aid in understanding the development of seed in three spikelet seed positions and the effects of treatments. An interaction of spring N and PGR resulted in increased seed yields in two of the three years while spring N and PGR worked independently in the other year to increase seed yield. The combination of TE and CCC PGRs did not increase seed yield over TE alone. Spring N effects on the observed increases in seed yield were largely due to a corresponding increase in seed number m−2 evident with spring N application. Increases in orchardgrass seed yield attributable to TE PGR were the result of increased seed number m−2 and improved harvest index (HI), but not seed weight. In 2018, seed weight increased over GDD in bi-phasic segmented pattern in seed from distal and central spikelets but increases were linear in seed from proximal spikelets. In 2019, seed weight increase in proximal spikelets followed a bi-phasic segmented function, while seed weight increase in central spikelets segmented except for TE treatment. Seed growth rate (SGR) varied among spikelet positions and ranged from 0.22 to 0.34 mg GDD-1 per 100 seed. The SGR varied among treatments and ranged from 0.31 to 0.47 mg GDD-1 per 100 seed. Seed filling duration (SFD) varied among spikelet positions and treatment. Seed moisture content declined over seed development in a linear manner in 2018, and the decrease in seed moisture followed mixed linear and segmented models in 2019. The TE + N treatment had both the shortest SFD and one of the shortest SGR values among treatments, and as a result tended to have low seed weight. The TE + N treatment produced high seed yields and seed number so either seed abortion or seed shattering loss was reduced, or both. The content of C and N in seed increased over growing degree days (P≤0.001) and followed a segmented model except for N content in the N treatment. Both C and N content of seed were increased by spring N application. The N treatment reached peak C deposition earliest and had the shortest duration of C filling in seed among the four treatments. The peak deposition of C and N preceded physiological maturity of the seed. During seed development, flag leaf chlorophyll declined in treatments with no N and either declined or were constant with N application. There were no consistent effects of TE PGR on the deposition of C or N in the seed. This study suggests that the combination of spring N applied at 112 kg N ha-1, and TE PGR application at 210 g ai ha-1 would be the best practice to increase seed yield in orchardgrass.
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