INFLUENCE OF DAYLENGTH AND IRRADIANCE ON GROWTH OF THE STOCK PLANTS AND SUBSEQUENT ROOTING OF CUTTINGS OF BETULA-UTILIS D-DON AND CORYLUS-MAXIMA MILL CULTIVAR PURPUREA

Two-year-old stock plants of Betula utilis D. Don. and Corylus maxima Mill. cultivar 'Purpurea' were etiolated in a darkroom or grown in a greenhouse under three different daylengths (8, 16 and 24 h). In each daylength, three different levels of irradiance were compared ( 100, 33 and 10%). After 3 weeks, the etiolated plants were transferred to the 8 or 16 h daylength with 100% irradiance. The cuttings from each stock plant treatment were rooted under 100, 33 or 10% irradiance. As standard cuttings were treated with 2% indole-3-acetic acid (IBA). The effect of IBA concentration (0, 0.5, 1 and 2%) was analysed separately. Reduction of the daylength or irradiance slowed down the maturation of the stock plants. For Betula, depending on the daylength, 100 or 33% irradiance proved optimal for rooting and regrowth. Etiolation followed by a 16 h day gave just as good results. Corylus cuttings rooted and regrew best when the stock plants were grown under 24 h daylength with 100 or 33% light, or under the 16 h daylength with 100% light, or in darkness followed by 16 h daylength. Rooting was mostly optimal under 33% irradiance. The longer the daylength, the more the IBA dose had to be reduced to achieve optimal rooting of Corylus. The same tendency was observed in Betula cuttings. In the best treatments the success rate of overwintering (in terms of number of cuttings taken) was over 90% in Betula and over 75% in Corylus.