EFFECT OF IRRADIANCE AND SPECTRAL COMPOSITION OF RADIATION ON IN-VITRO SHOOT PROLIFERATION IN MALUS-DOMESTICA BORKH

Four clones of Malus domestica Borkh. cv. Golden Delicious - namely Sm oothee, Crielaard, Reinders and Golden B - were cultured in vitro from single-node microcuttings placed on solid medium under irradiance (PP FD) of 50 mu mol m(-2) s(-1). After 9 months an average shoot prolifer ation of 5.3 was achieved; Crielaard showed the highest rate (7.1), fo llowed by Golden B (5.4), Smoothee and Reinders (4.4). Proliferating s hoots were then exposed to higher PPFD (80 mu mol m(-2) s(-1)) and dif ferent spectral composition of radiation using PMMA-B and PMMA-RIFR fi lters. High PPFD decreased the average proliferation rate to 4.5, in p articular in Crielaard and Golden B, while it increased proliferation in Reinders. When a PMMA-R/FR filter was interposed, the mean prolifer ation rate slightly increased. PMMA-B filters decreased the overall pr oliferation rate to 3.0; only in Crielaard it was increased, but shoot s were very small. Thus PPFD and spectral composition influenced in vi tro shoot proliferation and growth and the responses were different am ong the clones.