INITIATING CULTURES OF HALESIA AND MALUS - INFLUENCE OF FLUSHING STAGE AND BENZYLADENINE

Shoot tips of Halesia carolina L. and Malus domestica Borkh. 'Golden Delicious' collected at various times during the spring growth flush varied considerably in their ability to initiate shoot proliferating cultures. Shoot tips collected during, or at the end of, the period of most rapid shoot elongation exhibited weak shoot proliferation potential, while shoot tips collected before or after this period were capable of strong shoot proliferation in vitro. Benzyladenine concentrations in the culture media above 22.5 muM (Halesia) or 44.5 muM (Malus) were inhibitory during the period between bud break and rapid shoot elongation. Benzyladenine concentrations of 22.5 or 44.5 muM were useful in enhancing shoot proliferation potential in shoot tips collected after the period of rapid shoot elongation, but before the onset of summer dormancy. Benzyladenine concentration did not affect the shoot proliferation potential of shoot tips collected during the rapid shoot elongation phase of the spring growth flush. Halesia and Malus shoot tips behaved similarly in this study. For deciduous woody perennials, the time of explant collection for culture initiation could be refined on the basis of these results.