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Low Red to Far-Red Ratios Reaching the Stem Reduce Grain Yield in Sunflower

^a IFEVA, Buenos Aires, Argentina
^b Cátedra de Cultivos Industriales, Facultad de Agronomía, Univ. de Buenos Aires, Av. San Martín 4453, 1417 Buenos Aires, Argentina

View larger version (33K): [in a new window]   Fig. 1. Time course of stem length increment in three sunflower cultivars that received unfiltered sunlight red light/far-red light (R/FR) ratios (1.1, control) or low R/FR ratios (0.3) at the stem. First sowing date was 25 Oct. 1998. Second sowing date was 6 Jan. 1999. Bars indicate standard errors.

View larger version (16K): [in a new window]   Fig. 2. Relationship between final stem length and stem dry weight at grain harvest in sunflower plants that received sunlight red light/far-red light (R/FR) ratios (1.1, control) or low R/FR ratios (0.3) at the stem. Data include three genotypes (Guayacán II, Dekalb G100, and MA 566) and two sowing dates (25 Oct. 1998 and 6 Jan. 1999). Regression line corresponds to least squares fit significant at P < 0.01.

View larger version (34K): [in a new window]   Fig. 3. Length, dry weight, and dry weight/length ratio of the seventh internode of sunflower plants as affected by sunlight [control, red light/far-red light (R/FR) = 1.1] or low R/FR ratios (0.3) reaching the stem, and normal or reduced (40%) PAR reaching the whole shoot. The internode was harvested after reaching its maximum length. Bars indicate standard errors and the results of two-way ANOVA are shown (NS, not significant at the 0.05 level).

View larger version (15K): [in a new window]   Fig. 4. Yield of sunflower crops of different cultivars plotted against their average plant height at harvest. Open symbols correspond to 34 cultivars grown in Junín, Argentina (1995–1996). Closed symbols correspond to 24 cultivars grown in Pergamino, Argentina (1996–1997). Regression lines correspond to least squares fit significant at P < 0.01 (Junín) and P < 0.05 (Pergamino).