Tillering Responses ofLolium multiflorumPlants to Changes of Red/Far-Red Ratio Typical of Sparse Canopies

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