Paclobutrazol and Triadimefon Effects on Conifer Seedling Growth and Water Relations

1990

S. 722-729

4 Abb., 10 Tab., 21 Lit. Ang.

Unselbständiges Werk

200088611

Growth responses of Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) seedlings to the gibberellin synthesis inhibitor paclobutrazol were examined in sand culture. Shoot and root dry weights and root lengths were reduced at 5 mg (active ingredient) of paclobutrazol per litre, in the nutrient solution, although the proportion of dry matter allocated to roots was increased by 5 mg (active ingredient) of paclobutrazol per litre. Similar effects were observed with triadimefon, although the reduction in height growth was less in triadimefon-treated seedlings than in paclobutrazol- treated seedlings. Stomatal conductance, transpiration, and needle area: weight ratio were reduced by both paclobutrazol and triadimefon treatments of 13.5-weel-old-seedlings, although paclobutrazol was more effective than triadimefon in reducing needle area:weight ratio. Treatment of 1-year-old container seedlings of Douglas-fir and white spruce (Picea glauca (Moench) Voss) by shoot dipping or plug drenching with paclobutrazol, in December or March, reduced height growth and new needle area:weight ratio after 6 weeks growth in greenhouse. Xylem water potential of paclobutrazol-drenched seedlings was increased by 0.7 MPa above controls (-1.8 MPa) 11 weeks after planting, and stomatal conductance of drenched white spruce increased with paclobutrazol concentration.