The influence of cutting treatments with indole-3-butyric acid and boron, stock plant moisture stress, and shading on rooting in Sitka spruce

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Abstract
Methods of improving rooting of Sitka spruce (Piceasitchensis (Bong.) Carr) cuttings were studied. In experiment 1, cuttings from twenty-five 8- to 11-year-old trees were treated with five levels of indole-3-butyric acid (IBA) (0, 25, 50, 100, and 3000 mg L−1) and five levels of boron (B) (0, 0.5, 1.0, 5.0, and 10.0 mg L−1) in a factorial experiment. IBA was applied in a 24-h soak, except at 3000 mg L−1, when a 5-s dip was used. Greatest rooting was achieved with 25 mg IBA L−1 (55 vs. 38% for 0 mg IBA L−1), but rooting achieved with 3000 mg IBA L−1 (49%) was not significantly less. B had no effect on rooting. In a second experiment, 2-year-old stock plants, rerooted from hedges and 17 years from seed, were subjected to two watering treatments and three shading treatments applied factorially. Watering treatments were (i) normal watering to maintain moist soil in pots and ((i) low watering achieved by withholding water for 8 weeks in July and August. Shading treatments were (i) unshaded, (ii) shading from 1 July, and (iii) shading from 1 September until cuttings were removed in January. Shading reduced light intensity to 38% of full daylight. The low-watering treatment caused severe moisture stress and some mortality of stock plants. It also reduced rooting 16–24%, depending on the clone. Shading increased rooting 10–25%, depending on the clone, but there was little difference between times of shading.

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