Influence of different levels and timing of supplemental irradiation on pot chrysanthemum chrysanthemum morifolium cultivar paragon production
HortScience 20(3): 374-376
ISSN/ISBN: 0018-5345 Accession: 005683524
Supplemental photosynthetically active radiation (PAR; 77, 148 and 231 .mu.mol s-1 m-2) was provided to C. morifolium Ramat 'Paragon' during 14 days each of rooting (24 h daily), long days (LD; 24 h daily) or short days (SD; 9 h daily) in a greenhouse. Crop growth efficiency (calculated as the ratio of the observed to potential dry weight gain) was highest under the 77 .mu.mol s-1 m-2 treatment during each stage and decreased markedly at higher irradiances. Relative growth rates were increased by all levels of supplemental PAR at each stage. The increases were proportionately smaller than the increase in total PAR in treatments above 77 .mu.mol s-1 m-2. Flower number, and flower and vegetative dry weight increased in response to 77 .mu.mol s-1 m-2 supplemental PAR, but increased irradiances had no further effect. Extension of the 77 .mu.mol s-1 m-2 treatment beyond rooting to LD significantly improved all traits over single stage treatments. Further extension into SD, however, was not beneficial.