Paclobutrazol: A Promising Growth Inhibitor for Injection into Woody Plants

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Abstract

Paclobutrazol [(2RS,3RS)-1-(4-chlorophenyI)-4,4-dimethyl-2-(1,2,4-triazol-1-yl-)pentan-3-ol)] was injected into bean plants (Phaseolus vulgaris L. ‘Black Valentine’), California privet seedlings (Ligustrium ovalifolium Hassk.), saplings of red maple (Acer rubrum L.), yellow poplar (Liriodendron tulipifera L.), white ash (Fraxinus americana L.), American sycamore (Platanus occidentalis L.), and one-year-old trees of ‘Golden-Delicious’ apple (Malus domestica Borkh), to evaluate growth inhibition response. Also, the extent of translocation and metabolism of injected ¹⁴C — paclobutrazol was determined in apple. The height growth, weight, and leaf size of bean plants decreased as the dose of paclobutrazol increased from 0.01 to 1,000 μg/plant. Sprout growth from stumps of privet was reduced as the dose of paclobutrazol increased from 1 μg to 1000 μg/tree. The shoot growth of sapling trees in the field was controlled for at least 2 months with doses of paclobutrazol ranging from 5 mg to 40 mg per tree. When obvious inhibition occurred in apple trees (27 days after injection), 23% of the ¹⁴C-activity had been translocated acropetally to the apical shoots. A high percentage of ¹⁴C-activity detected was paclobutrazol; 90% of the ¹⁴C-activity found in the xylem and phloem and over 85% in the shoot tissue chromatographed with paclobutrazol.

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