Response of Pot Chrysanthemum to Supplemental Irradiation during Rooting, Long Day, and Short Day Production Stages

Abstract

Chrysanthemum × morifolium Ramat cv. Paragon plants were grown under supplemental irradiation from high-pressure sodium lamps during rooting, long day (LD), and short day (SD) production stages in all combinations. Plants which were rooted under supplemental irradiation had higher relative growth rates (RGR) and dry weight increments during that stage than nonirradiated controls. Supplemental irradiation similarly increased RGR and dry weight increments during LD and 5 weeks of SD. Root, top, and total dry weights at the end of the SD irradiation period showed a residual incremental effect of the LD treatment. Percentage of increases in dry weight increments due to supplemental irradiation were quite consistent between stages, whereas treatments had a greater effect on RGR during rooting and LD than during SD. The number of days to final harvest was reduced by supplemental irradiation during rooting and LD. The numbers of flowering stem breaks per pot, mean stem break length, and total plant dry weight were increased by supplemental irradiation at each stage. Those effects principally were additive. Flower dry weight per plant was increased significantly only by LD treatment. The benefits of supplemental irradiation during each production stage, and of combined treatments, are discussed in relation to operating costs.

Physiological Response of Rhododendron Cuttings to Different Light Levels During Rooting

“…Plant size 2 months after the rooting period was unaffected by light level during rooting, in contrast to work with chrysanthemum (13), where a high irradiance-(5.9 vs. 1.5 MJ-m~2-day_1) induced size advantage at the end of the rooting period persisted long afterwards. The observation that our 95% shade-rooted cuttings overcame their size disadvantage indicates that they adapted to the relatively high light during post-propagation growth.…”