Effects of supplementary irradiance on flowering time of obligate long day ornamental annuals under non-inductive environment

Seeds of five obligate ldps (pot marigold cv. resina,annual phlox cv. astoria magenta,cornflower cv. florence blue,oriental poppy cv. burning heart and flax cv. scarlet flax) were sown into module trays containing homogeneous leaf mould compost. after germination,saplings of each cultivar were shifted into four light intensity chambers (42,45,92 and 119μmol.m-2.s-1) for a duration of 8h (from 08:00 to 16:00h). the findings of this study showed that obligate ldps grown under high irradiance (92 and 119μmol.m-2.s-1) flowered earlier. however,there was a non-significant difference between 42/45μmol.m-2.s-1 and 92/119μmol.m-2.s-1 irradiance levels. although obligate ldps under 119μmol.m-2.s-1 flowered few days earlier than those received 92μmol.m-2.s-1 irradiance but the quality of plants (plant height and leaf size/appearance) was inferior. it is therefore concluded that for better plant quality and early flowering obligate ldps should be grown under 92μmol.m-2.s-1 irradiance.