• Eysteinsson, Throstur
  University of Maine
  

One of the principal methods used to accelerate the process of breeding trees is early induction of flowering. Flowering was promoted on potted, indoor and field-grown 3-year-old juvenile and mature Larix laricina (Du Roi) K. Koch grafts, by foliar sprays of the plant growth regulator gibberellin (GA4/7) and root pruning (RP). Biweekly GA4/7 applications of 3 different durations, commencing at the start of long shoot elongation, yielded similar increases in female flowering in the greenhouse, and this effect was synergistically enhanced by RP. Male flowering was promoted by GA4/7 + RP in mature but not juvenile grafts. Un the field, female flowering was also promoted by the GA4/7 treatment commencing at the start of shoot extension, but GA4/7 applications starting later were not effective. Grafted scions from mature trees responded significantly better to GA4/7 + RP than did seedling scions.