Effects of three plant growth regulators upon growth patterns in seedlings of three races of Douglas-fir, Pseudotsuga menziesii (Mirb.) Franco

Graduation date: 1967Populations of Douglas-fir seedlings from interior British\ud Columbia, Vancouver Island, and Arizona received six bi-weekly\ud foliar spray applications of the growth regulators IAA, CCC, and\ud B-995, each at three concentration levels under controlled environmental\ud conditions. Large differences were found among the three\ud populations in their responses to the growth regulators. The responses\ud to IAA treatments were as follows: height growth of interior\ud British Columbia seedlings was reduced markedly by all\ud three concentrations, Vancouver Island seedlings were unaffected\ud by all concentrations, and only the lowest concentration (75 ppm)\ud reduced the height growth of the Arizona seedlings; 300 ppm caused\ud twisting of leaders and a marked increase in the number of periods\ud of dormancy in all seedlings; and top dry weight was affected only\ud (Degree)\ud in interior British Columbia seedlings, particularly by 300 ppm.\ud Although the number of periods of dormancy was markedly increased\ud by 300 ppm IAA in the Vancouver Island and Arizona seedlings, height\ud growth was the same as in untreated seedlings. Root dry weights\ud varied in an inconsistent manner throughout the experiment. The\ud responses to CCC treatments were as follows: 2000 ppm reduced\ud height growth and top dry weight of interior British Columbia and\ud Vancouver Island seedlings but had no significant effect on the\ud Arizona seedlings. With increasing concentrations internodes became\ud progressively shorter and chlorosis more intense. CCC had\ud little effect upon number of periods of dormancy. The responses to\ud B-995 were as follows: height growth and number of periods of dormancy\ud were both decreased in Arizona seedlings; interior British\ud Columbia and Vancouver Island seedlings were affected to a lesser\ud degree. B-995 had no effects on top or root dry weight.\ud In a separate experiment, the effects of the high concentrations\ud of the three growth regulators upon the time of break of dormancy\ud were determined. Dormant 1-0 Douglas-fir seedlings lifted from a\ud nursery bed in mid-February were treated once or twice using either\ud two percent dimethyl sulfoxide (DMSO) or water as carrier. The\ud containers of seedlings were then transferred to a growth chamber\ud and exposed to an environment favorable toward growth initiation\ud (same environment as first experiment). Only 2000 ppm of CCC applied twice using water as carrier slowed the rate of growth\ud initiation significantly