GROWTH AND PROLIFERATION IN-VITRO OF VACCINIUM-CORYMBOSUM UNDER DIFFERENT IRRADIANCE AND RADIATION SPECTRAL COMPOSITION

Plantlets of highbush blueberry (Vaccinium corymbosum) cvs. Atlantic, Berkeley and Elizabeth, were exposed in vitro to radiation of differen t spectral compositions obtained by filtering the cool-white light wit h either 2 types of polymethylmethacrylate (PMMA) layers or glass and different photosynthetic photon flux density (PPFD, ranging from 10 to 180 mu mol m(-2) s(-1)). Red colour of leaves was the first response to the light treatments: after 14 d under unfiltered light, the shoots exposed to higher PPFD showed dramatic reddening of leaves and sprout s, especially in cv. Atlantic; cutting wavelengths shorter than 520 nm (no-B-PMMA filter) prevented those effects. On average, cv. Atlantic yielded the highest number of shoots per explant (10.4), followed by c v. Elizabeth (9.1) and cv. Berkeley (6.5). No-B-PMMA increased the pro liferation rate in all the 3 genotypes, especially in cv. Atlantic. On the other hand, cutting wavelengths between 650 and 760 nm (no-R-PMMA filter) generally depressed the proliferation rate. No-B-PMMA induced remarkable changes in the morphology of the shoots - more elongate le aves and longer internodes - especially in cv. Atlantic.