LIGHT EFFECTS ON IN-VITRO ROOTING OF PEAR CULTIVARS OF DIFFERENT RHIZOGENIC ABILITY

The effect of varying light regimes on in vitro rooting of microcuttin gs of two pear (Pyrus communis L.) cultivars was investigated. Culture s of the easy-to-root 'Conference' and the difficult-to-root 'Doyenne d'Hiver' were incubated for 21 days with or without indole-3-butyric a cid (IBA) in the medium in darkness or under continuous far-red (8 mu mol m(-2) s(-1), blue, white or red (15 or 36 mu mol m(-2) s(-1)) ligh t. 'Conference' rooted without IBA when exposed to red, blue or white light while no rooting was observed under far-red light and in darknes s. The high rooting efficiency under red and, by contrast, the inhibit ion under far-red light and darkness suggest the involvement of the ph ytochrome system in rhizogenesis. The addition of IBA to the culture m edium enhanced root production under all light regimes in both cultiva rs. Red light, especially at the lower photon fluence rate, had a posi tive effect by increasing root extension (number X length of roots) an d stimulating secondary root formation.