JUVENILITY, FLOWERING, AND THE EFFECTS OF A LIMITED INDUCTIVE PHOTOPERIOD IN COREOPSIS-GRANDIFLORA AND C-LANCEOLATA

Juvenility and flowering requirements of Coreopsis grandiflora Hogg ex Sweet. 'Sunray' and C. lanceolata L. 'Early Sunrise' were examined by growing plants under short days (SD) and transferring them to long days (LD) upon reaching the designated true leaf stages. Neither cultivar flowered in continuous SD, and 'Sunray' remained vegetative in LD. However, LD induced flowering in 'Early Sunrise' plants in each leaf count treatment and the loss of juvenility was gradual, with most rapid flowering occurring when plants were transferred to LD at the 16 leaf stage. The limited inductive photoperiod (LIP) inhibited stem elongation of 'Early Sunrise' plants in all LD treatments and selectively inhibited axillary flower bud development compared to plants grown in continuous LD. LIP did not affect scape length at first flower even though plant height was significantly diminished if given relatively few LD before transfer to SD. Height reduction was attributed to LIP inhibition of stem elongation with no significant loss of axillary flower bud potential.