Tillering Responses of Lolium multiflorum Plants to Changes of Red/Far-Red Ratio Typical of Sparse Canopies

Casal, J. J., Sáchez, R. A. and Deregibus, V. A. 1987.Tillering responses of Lolium multiflorum plants to changesof red/far-red ratio typical of sparse canopies.—J. exp.Bot. 38: 1432–1439. Plants of Lolium multiflorum were grown either in growth roomsunder radiation sources providing equivalent PAR but differentR/FR ratios between 0·46 and 2·36, or under sunlightsupplemented with a series of small fluence rates of FR throughoutthe photoperiod. In both kinds of experiments a reduction oftillering was found along with small depressions of R/FR ratiobelow the values typical of sunlight. In this range both thesquare-root-transformed rate of tillering and the site-fillingrate were linearly related to the estimated phytochrome photo-equilibriaand the slope was very steep under conditions that allowed hightillering rates. The addition of low fluence rates of red lightat the base of the shoots raised tillering of plants exposedto low R/FR ratios to the level of plants grown under high R/FRratios in spite of the ratios received by the rest of the plant.Moreover, irradiation of plant bases with intermediate-low R/FRratios reduced tillering indicating that this would be one siteof perception. These results show a high sensitivity to changesof R/FR ratio typical of different degrees of shade in sparsecanopies. This suggests that by monitoring these changes Loliummultiflorum plants would be able to perceive an anticipatedsignal of impending competition in growing canopies.