PHOTOSYNTHETIC CAPACITY, PHOTOPERIOD, AND SHOOT ELONGATION OF HARDY EVERGREEN AZALEAS (RHODODENDRON) CULTIVARS

Abstract

In a June-July greenhouse experiment photosynthetic capacity (Pcap) and shoot elongation were determined for 13 azalea cultivars. While the positive correlation between shoot elongation and Pcap was relatively low, the 2 cultivars with the highest rate of shoot elongation (`Treasure' and `Noordthiana') had the highest Pcap. In October-January greenhouse experiments, `Treasure and `Noordthiana' had highest rates of shoot elongation, but only `Treasure' had a high Pcap and `Noordthiana' had a very low Pcap. A growth chamber experiment showed that while long days stimulated shoot growth (compared to short days) they had no influence on Pcap. Gibberellin sprays stimulated shoot growth of `Vuyk's Scarlet' in the greenhouse during June-July but had no effect on Pcap. During November-January in the greenhouse long days stimulated shoot growth and in both summer and winter periods production time of cultivars with a rapid rate of shoot elongation was considerably less than for slower-growing cultivars, although rates of shoot elongation were much slower during winter periods.