EFFECTS OF YEAR-ROUND SUPPLEMENTARY LIGHTING ON SHOOT DEVELOPMENT, FLOWERING AND QUALITY OF 2 GLASSHOUSE ROSE CULTIVARS

The cut rose cultivars 'Korflapei' Frisco(R) and 'Bergme' Gabriella(R) were subjected to 12 equally spaced supplementary photosynthetic photon flux density (PPFD) levels, 0-174 mumol s-1 m-2. Supplementary-lighting was supplied by high pressure sodium (HPS) lamps for 20 h day-1 all year, whenever the natural PPFD level inside the glasshouse dropped below 75 mumol s-1 m-2. Supplementary PPFD and yield and quality were linearly related. Increasing PPFD by a constant quantity had a consistent effect on rose yield throughout the year. At a supplementary PPFD of 87 mumol s-1 m-2 Frisco(R) yielded 62% and Gabriella(R) 33% more saleable blooms per square metre of bed area per year compared with traditional cultivation without supplementary lighting. In addition, the percentage of first grade blooms was enhanced by 4-8%, while the percentage of blind shoots was halved. Fresh weight was enhanced by 55% and 56% and stem length by 10% and 13% for Frisco(R) and Gabriella(R), respectively and Gabriella(R) stem diameter increased by 19% when supplementary PPFD was increased from 0 to 174 mumol s-1 m-2. Frisco(R) utilized supplementary PPFD better than Gabriella(R). Possible mechanisms for the effects of supplementary lighting on cut rose growth and development are discussed.