Influence of Light Duration and Irradiance on Micropropagation of a Hardy Deciduous Azalea

Abstract

Abstract Shoots harvested from the first and 2nd reculture of azalea (Rhododendron sp.) accession 800374 shoot tip cultures grown under 16 hr photoperiod from cool-white fluorescent light were taller and achieved higher quality ratings than shoots from 24 hr daily photoperiod. The number of shoots produced during the first reculture was the same for both 16 and 24 hr photoperiod, whereas significantly more shoots were harvested from cultures grown under 16 hr in the 2nd reculture. Similarly, 24 hr light inhibited elongation of shoots and decreased quality rating from in vitro-derived shoot cultures without any effect on the number of shoots per culture. Photosynthetic photon flux density (PPFD) of 30 and 75 μmol s−1m−2 (400–700 nm) increased number, length, and quality rating of shoots harvested from in vitro-derived shoot explants when compared to a 10 μmol s−1m−2 PPFD. However, recultured in vitro-derived shoot explants produced similar number and length of shoots under 10, 30, and 75 μmol s-1m-2, whereas the quality rating was reduced in cultures under 75 μmol s−1m−2. The highest percentage of rooting occurred in microcuttings harvested from cultures grown under 10 and the lowest under 75 μmol s−1m−2. Increasing the PPFD from 10 to 75 μmol s−1m−2 reduced shoot length and quality rating of rooted microcuttings, as well as root length and quality rating.