Effect of red light on ex vitro rooting of rose and gerbera microcuttings in rockwool

Microcuttings of rose cv. Sonia and cv. Sabrina, and gerbera cv. Rebecca were rooted ex vitro in rockwool (Grodan SBS) in a greenhouse. In order to stimulate rhizogenesis the shoots were treated with red light at 3 mumol M-2S-1 photosynthetic photon flux density (PPFD) emitted from fluorescent lamps for 4h during the night for periods of 3, 7, 14 and 42 nights, while half of the microcuttings were treated with auxin solutions. The irradiation of shoots for 7-14 nights with red light during the ex vitro rooting highly influenced root formation both in rose and gerbera. The seasonal and genotype differences in response to red light were noted. In rose 'Sabrina', red light promoted root formation during plantings in March, May and November, increasing the growth of shoots, root system quality and percentages of rooted microcuttings from below 50% (control microcuttings) up to 80-100%. In July, the best rooting was noted in the control microcuttings which were not treated with auxins or red light. In rose cultivar 'Sonia', the positive effect of red light on rooting ex vitro was found both in winter and summer. In gerbera, red light irradiation improved rooting only during winter (in February), enhancing the percentage of rooted microcuttings from 67.1% (control microcuttings) to 86.1 % -98.6 % in each red light treatments.