ROUSSEAUX Maria Cecilia
Far-red enrichment and photosynthetically active radiation level influence leaf senescence in field-grown sunflower.-
ROUSSEAUX, M. C.; HALL, A. J; SANCHEZ, R. A.
WILEY-BLACKWELL PUBLISHING, INC
Año: 1996 vol. 96 p. 217 - 224
Basal leaves frequently senesce before anthesis in high population density crops. This paper evaluates the hypothesis that quantitative and qualitatives changes in the light environment associated with a high leaf area index (LAI) trigger leaf senescence in sunflower (Helianthus annuus L.) canopies. Mean leaf area duration (LD, time from achievement of maximum leaf area) of leaf 8 was significantly (P<0.05) reduced from 51 to 19 days as crop population density increased from 0.47 to 4.76 plants m-2. HIgh compared to low plant density was associated with earlier reduction in the photosynthetically active radiation (PAR) and re/far-red ratio (R/FR) reaching the target leaf. owever, the changes in R/FR preceded those in PAR. When the light environment of individual leaves of isolated plants growing under field conditions was manipulated using filters and FR-enrichment mirrors, LD was positively and linearly related with the mean daily PAR (MDR) received in the FR- (no FR enrichment) treatments. FR enrichment of light reaching the abaxial surface of the leaf significantly (P<0.05) reduced LD by 9 days at intermediate PAR levels with respect to FR-controls, but did not affect LD at the maximum PAR used in these experiments. However, when light reaching both surfaces was enriched with FR, LD (for leaves receiving maximum PAR) was 13 days shorter than that of the FR-control. These results show that basal leaf senescence in sunflower is enhanced both by a decrease in PAR and by a decrease in R/FR.