Effects of light quantity and quality on intermediate wheatgrass tillering dynamics: A comparison with annual wheat

Growing intermediate wheatgrass (IWG), a perennial grass undergoing domestication, for grain production in dense swards entails a substantial modification of the light environment that drives plant growth. In the present study, we investigated the decoupled effects of light quantity and quality on IWG tillering dynamics, in comparison to that of winter wheat. Plants were grown in pots in semi-controlled conditions under light filters with 5 different levels of red-to-far red ratio (R:FR) ranging from 0.17 to 1.09 and with 28% of transmitted photosynthetic photon flux density (PPFD). A control treatment with 96% of PPFD and R:FR of 1.09 was added. For each plant, tillers were identified and monitored individually until maturity. Irrespective of the light conditions, IWG tillering dynamics was slower than that of wheat, and with no regression, which was attributed to differences in growth and life strategies. The light treatments had an effect on tiller emission at the earliest stages of plant development, which was mainly explained by the inhibition of bud outgrowth. Following the flag leaf stage, IWG exhibited no tillering cessation nor regression, in contrast with wheat for which the extent of tiller regression was associated with the plant tiller density. Spike production was linearly correlated with the number of tillers, indicating that the light conditions did not affect the ability of tillers to outgrow spikes. By deepening our knowledge of IWG tillering response to light, and how it differs from that of annual wheat, this study brings important information for further breeding efforts and study of agronomic practices.