Chronology of three physiological development phases of single-stemmed rose (Rosa hybrida L) plants in response to increment in light quantum integral

It has been suggested that light mainly affects rose plant development time from the onset of bud growth until the flower bud becomes visible. The effects of increased light quantum integral on the duration of three physiological development phases from excision/planting of single-node cuttings until anthesis of single-stemmed rose plants were studied. Cuttings/plants of cut rose cultivars 'Kordapa' Lambada(R), 'Tanettahn' Manhattan Blue 'Tanorelav' Red Velvet(R) and 'Sweet Promise' Sonia(R) were grown in long photoperiods at high air temperature and high plant densities, in rockwool cubes on ebb-flow units, irrigated with a complete nutrient solution and supplied with carbon dioxide to a level of 1000 mu l l(-1). By increasing the daily light quantum integral from 17.8 to 21.0 mol m(-1) per day during all three development phases; excision/planting to onset of bud growth, onset of bud growth to visibility of flower bud, and visibility of flower bud to anthesis, there was a significant reduction in the time needed for plant development. The effects, however, were more apparent after the onset of bud growth, which included the second and third growth phases, during which time the reduction in days was about 25% more than that observed prior to the onset of bud growth. While the four cultivars reacted similarly, variation in plant population density modified the effects of the increased light quantum integral, resulting in clear effects at the lower plant density of 100 plants per m(2). The modest increment in average daily quantum integral, about 18%, almost halved the percentage of blind shoots formed, indicating a fairly high critical light level for this parameter. These effects are suggested to be related to both the assimilate supply and the light perception of the roses.