Speaker
Description
Introduction
Agronomic studies on the use of intermediate wheatgrass (Thinopyrum intermedium) as a perennial grain crop show a grain yield decline over the years, which calls for a better understanding of the link between Th. intermedium vegetative development and investment in reproduction. Recent data suggest that density and row spacing might influence yield components in Th. intermedium (Fernandez et al. 2020; Hunter et al. 2020). Light is a major factor driving morphological and physiological changes with plant density. It could influence grain yield, both indirectly through tillering and directly by affecting yield components. Tillering is critical for the reproductive stage of perennial grasses and is very plastic to the light environment: notably a decrease of the red:far-red light ratio (R:FR ratio) is known to reduce tillering (Casal et al. 1985). Therefore, this study addresses the effects of light quantity and quality on the tillering dynamics and yield components of Th. intermedium.
Materials & Methods
Plants were sown in a growth chamber and vernalized for 7 weeks at 3 leaves. In total, 72 plants were transplanted and placed in a tunnel under light filters. Five R:FR treatments were tested: 1.09 (natural light), 0.55, 0.44, 0.30, 0.17. Between 27 and 29% of PAR was transmitted by the filters. A control was added with a R:FR of 1.1 and 96% of transmitted PAR.
Each new tiller was marked every week, specifying order and position on the mother tiller. Haun stage was noted for every tiller, every week up to flag leaf stage. Then, heading and flowering were noted. New tillers developing after flowering of the main stem were not monitored. Height of the main stem was measured up to flag leaf. All plants were harvested when a majority of spikes was mature. At harvest, the total number of tillers, rhizomes and spikes were counted. Plants were dried (40°C for 3 days) before weighing vegetative dry biomass. Measures for each spikes included dry weight, number of spikelets, number of florets on 3 spikelets (basal, middle, apical), number of grain and grain weight.
Results
In the control, height of the main stem was significantly shorter throughout its development and the difference with the other treatments kept increasing over time. Interestingly, no significant effect of R:FR was observed on height except for lowest R:FR treatment (R:FR=0.17). R:FR treatments had more impact on tiller number. Lower PAR reduced tiller emergence, so did lower R:FR. Differences between R:FR treatments were only significant between the 1.09 and the 0.44 and 0.30. Both primary and secondary tillers emergence were inhibited by decreasing PAR and R:FR, and tertiary tillers mostly appeared in the control. Surprisingly, the lowest R:FR treatment had the highest number of tillers after the control and the 1.09. Phyllochrons of main stems, primary and secondary tillers were affected by R:FR treatments, but within each treatment only the control had significantly different phyllochrons between tiller orders. Effects on yield components are still under study (sample being processed) and will be presented during the conference.
Discussion
These results highlight that tillering plasticity to the light environment is high in Th. intermedium. This means that current populations of Th. intermedium should be very sensitive to plant density, leading to competition for light and adaptation to light quality. Therefore, increasing light penetration at the base of the canopy at specific times of the crop cycle (using planting density, cuttings and post-harvest management practices) may be an agronomic lever to manage tillering dynamics and investment in reproduction over the years, although it has to be tested in field conditions. Furthermore, this study provides physiological information on the tillering dynamics and leaf development of Th. intermedium for different tiller orders, which can be used to favour productive tillers.
References
Casal JJ, Deregibus VA, Sanchez RA (1985) Variations in Tiller Dynamics and Morphology in Lolium multiflorum Lam.Vegetative and Reproductive Plants as affected by Differences in Red/Far-Red Irradiation. Annals of Botany 56:553–559. https://doi.org/10.1093/oxfordjournals.aob.a087040
Fernandez CW, Ehlke N, Sheaffer CC, Jungers JM (2020) Effects of nitrogen fertilization and planting density on intermediate wheatgrass yield. Agronomy Journal 112:4159–4170. https://doi.org/10.1002/agj2.20351
Hunter M, Sheaffer C, Culman S, Jungers J (2020) Effects of defoliation and row spacing on intermediate wheatgrass I: Grain production. AGRONOMY JOURNAL 112:1748–1763. https://doi.org/10.1002/agj2.20128
| Keywords | Thinopyrum intermedium; tillering; light quality; light quantity; grain yield |
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