EFFECT OF GA4/7 AND STEM GIRDLING ON SHOOT GROWTH IN Pseudotsuga menziesii (Mirb.) Franco

Abstract

To evaluate potential negative collateral effects of flower induction treatments applied to juvenile Pseudotsuga menziesii trees on crown development (GA_4/7 application, stem girdling on shoot elongation, and the impact of female cones (strobili) induction on shoot elongation), were evaluated. Induction treatments were applied in two field trials with 10 to 13-years-old trees (Trials 1 and 2) and one pot trial in the nursery with 4-years-old trees (Trial 3). Four doses of GA_4/7 (0, 1.27, 2.55 and 5.10 mg cm^-2 basal area), applied by injection into the tree trunk, combined with stem girdling (with or without girdling) were evaluated. During the growing period the total length of shoots was measured and the average growth curve was adjusted using the Schumacher model. Differences in shoot length were found across trials as well as among GA_4/7 doses and girdling levels, but no significant interactions between factors were detected. In Trial 1, shoots grew 30 % more than in the others, but in Trial 2 shoot growth started first and reached highest maximum growth rate; the youngest trees in Trial 3 showed the shortest shoot length. Stem girdling reduced shoot growth by 9 % and slowed it by 6 d, whereas GA_4/7 increased 12 % the final shoot length and accelerated its growth. The induction of female cones caused a slight delay in the shoot growth curve, but final shoot length was not reduced. Use of GA_4/7 in doses of 1.27 mg cm^-2 to induce flowering in juvenile trees of P. menziesii did not have negative effects on shoot growth; however, repeated use of stem girdling could negatively affect tree growth and vigor.