Effect of Photoperiod and Irradiance on Floral Development of Young Plants of a Semi-early and a Late Cultivar of Azalea

Abstract

For 2 cultivars of azalea ( Rhododendron sp.), floral initiation was earlier when irradiance was increased from 80 to 160 µE m -2 s -1 . Buds aborted at an early stage of floral initiation in 8-hr days, but this was prevented by increasing the irradiance from 80 to 250 µE m -2 s -1 . A night interruption of 1.5-hr incandescent light allowed plants kept in 8-hr days to grow vegetatively for a longer time. Inflorescence development increased with increasing daylength and irradiance. In the late cultivar ‘Knut Erwén’, inflorescence development was reduced by low light intensities more than in the semi-early ‘Reinhold Ambrosius’.