Photosynthetic daily light integral during the seedling stage influences subsequent growth and flowering of Celosia, Impatiens, Salvia, Tagetes, and Viola

Additional index words. bedding plants, marigold, pansy Abstract. The photosynthetic daily light integral (DLI) dramatically increases during the spring when the majority of bedding plants are commercially produced. However, the effects of DLI on seedling growth and development have not been well characterized for most bedding plant species. Our objectives were to quantify the effects of DLI on growth and development of Celosia, Impatiens, Salvia, Tagetes, and Viola during the seedling stage and determine whether there were any residual effects of DLI on subsequent growth and development after transplant. Seedlings were grown in growth chambers for 18 to 26 days at 21 °C with a DLI ranging from 4.1 to 14.2 mol·m -2 ·d -1 . Average seedling shoot dry weight per internode (a measure of quality) increased linearly 64%, 47%, 64%, and 68% within this DLI range in Celosia, Impatiens, Tagetes, and Viola, respectively. Seedlings were then transplanted to 10-cm containers and grown in a common environment (average daily temperature of 22 °C and DLI of 8.5 mol·m -2 ·d -1 ) to determine subsequent effects on plant growth and development. Flowering of Celosia, Impatiens, Salvia, Tagetes, and Viola occurred 10, 12, 11, 4, and 12 days earlier, respectively, when seedlings were previously grown under the highest DLI compared with the lowest. Except for Viola, earlier fl ower- ing corresponded with the development of fewer nodes below the fi rst fl ower. Flower bud number and plant shoot dry weight at fi rst fl owering (plant quality parameters) decreased as the seedling DLI increased in all species except for fl ower number of Tagetes. Therefore, seedlings grown under a greater DLI fl owered earlier, but plant quality at fi rst fl owering was generally reduced compared with that of seedlings grown under a lower DLI.