Radiation Intensity and Quality from Sole-source Light-emitting Diodes Affect Seedling Quality and Subsequent Flowering of Long-day Bedding Plant Species

Previous research has shown high-quality annual bedding plant seedlings can be produced in controlled environments using light-emitting diode (LED) sole-source lighting (SSL). However, when only red and blue radiation are used, a delay in time to flower may be present when seedlings of some long-day species are subsequently finished in a greenhouse. Thus, our objectivewas to evaluate the effects of various radiation qualities and intensities under SSL on the morphology, nutrient uptake, and subsequent flowering of annual bedding plant seedlings with a long-day photoperiodic response. Coreopsis (Coreopsis grandiflora 'Sunfire'), pansy (Viola 3wittrockiana 'Matrix Yellow'), and petunia (Petunia 3hybrida 'Purple Wave') seedlings were grown at radiation intensities of 105, 210, or 315 mmol.m(-2).s(-1), achieved from LED arrays with radiation ratios (%) of red:blue 87:13 (R-87:B-13), red:far-red:blue 84:7:9 (R-84:FR7:B-9), or red:green:blue 74:18:8 (R-74:G(18):B-8). Four-week-old seedlings were subsequently transplanted and grown in a common greenhouse environment. Stem caliper, root dry mass, and shoot dry mass of seedlings generally increased for all three species as the radiation intensity increased from 105 to 315 mu mol.m(-2).s(-1), regardless of radiation quality. Similarly, stem length of all three species was generally shorter as the radiation intensity increased. Macro- and micronutrient concentrations were also generally lower as the radiation intensity increased for all three species. Pansy seedlings grown under R-84:FR7:B-9 flowered an average of 7 and 5 days earlier than those under R-87:B-13 and R-74:G(18):B-8, respectively. These results provide information regarding the specific radiation parameters fromcommercially availableLEDs necessary to produce high-quality seedlings under SSL, with radiation intensity appearing to be the dominant factor in determining seedling quality. Furthermore, the addition of far-red radiation can reduce time to flower after transplant and allow for a faster greenhouse turnover of some species with a long-day photoperiodic response.