The significance of changes in the red/far‐red ratio, associated with either neighbour plants or twilight, for tillering in Lolium multiflorum Lam.

Abstract

SUMMARYLolium multiflorum Lam. plants were used to investigate whether phytochrome-mediated tillering responses, anticipatory to competition: (a), are potentially disturbed by the twilight drop in the red to far-red ratio (R:FR) of sunlight (caused by atmospheric factors), and {b), occur in densely-sown (> 280 plants m~^) grass canopies, where competition is quickly established.Isolated plants grown under sunlight received natural low R: FR during twilight, but supplementary R provided simultaneously did not increase tillering. When a wide range of R: FR was provided at the end of natural or fluorescent light photoperiods, tillering was reduced only by very low R:FR (lower than natural twilight R:FR). Leaf sheath length followed a similar pattern of response.Single plants were grown in pots placed at various densities. High densities reduced the R:FR at plant bases and the number of tillers per plant before changes in dry weight and leaf number were found.Both very low R:FR provided at the end of the photoperiod, and increasing plant densities, caused more erectophile shoots.In densely-sown canopies of Lolium multiflorum both R:FR signals caused by neighbours, and tillering responses occur well before strong competition is established. Tillering is not obviously affected by the twilight drop in R:FR.

Variation in growth form in relation to spectral light quality (red/far-red ratio) in Plantago lanceolata L. in sun and shade populations

“…Nevertheless, no selection for an increased number of leaves in juvenile plants was apparent in tall vegetation (van der Toorn and Pons 1988). Increased plant height is often accompanied by a decrease in branching or leaf production as a result of increased apical dominance under low R/FR ratios (e.g., Casal et al 1990;Smith 1982). Suppressed branching is thought to be bene®cial in tall vegetation because lower branches will have no chance to escape from shading (Smith 1982).…”

“…Changes in the R/FR ratio beneath a canopy are closely related to vegetation height and seem a reliable cue for light competition (Casal and Smith 1989). Far red light re¯ected from neighboring plants might trigger phenotypic responses by in¯uencing the phytochrome photoreceptor even before the actual shading takes place (Ballare et al 1988(Ballare et al , 1990Casal et al 1986;Novoplansky 1991;Novoplansky et al 1990).…”

The function of phytochrome A

“…In wildtype plants, phyA would set a high sensitivity to changes in R/FR during daytime (when phyA is active) and a low sensitivity to changes in twilight R/FR. Both dicotyledonous and grass seedlings are more sensitive to changes in R/FR during daytime than to changes in end-of-day R/FR at equal day/night temperature (Casal & Smith 1989;Casal, Sanchez & Gibson 1990). …”

Modeling branching in cereals

“…Cereal plants are able to maximize total plant light capture and grain production through processes such as bud dormancy break, tiller development, and tiller senescence. These processes are highly plastic: the growing conditions a cereal plant experiences strongly influence the tillering characteristics of the plant (e.g., Casal et al, 1990; Rodríguez et al, 1999; Lafarge and Hammer, 2002; Evers et al, 2006; Sparkes et al, 2006). At high population densities, bud break is generally low and tiller mortality is relatively high (Darwinkel, 1978).…”