Paclobutrazol

Paclobutrazol, PBZ (chemical name (2RS, 3RS)-1-(4-Chlorphenyl)-4,4-dimethyl-2-(1H-1,2,4-triazol-1-yl)pentan-3-ol) is a plant growth retardant and triazole fungicide. It is a known opponent of the plant hormone gibberellin. It acts by inhibiting gibberellin biosynthesis, reducing internodial growth to give stouter stems, increasing root growth, causing early fruitset and increasing seedset in plants such as tomato [Berova and Zlatev, "Physiological response and yield of paclobutrazol treated tomato plants" Plant Growth Regulation, Volume 30, Number 2, February 2000 [http://www.springerlink.com/index/VG02K661X2N0PG32.pdf] ] and pepper. [Grossi "et al.", "Effects of paclobutrazol on growth and fruiting characteristics of "Pitanga" ornamental pepper" Acta Horticulturae, 2005 (No. 683) 333-336] PBZ has also been shown to reduce frost sensitivity in plants.PBZ is used by arborists to reduce shoot growth and has been shown to have additional positive effects on trees and shrubs. Among those are improved resistance to drought stress, darker green leaves, higher resistance against fungi and bacteria, and enhanced development of roots. [Chaney "et al." 1996; Fletcher "et al." 2000; Rademacher 2000; Chaney 2003] Cambial growth as well as shoot growth has been shown to be reduced in some tree species. [Bai "et al." 2004]

Application methods

PBZ is normally applied to the soil to be taken up by the roots and transported via the xylem to the upper parts of the plant. Foliar application is mostly ineffective. [Grossi "et al.", "Effects of paclobutrazol on growth and fruiting characteristics of "Pitanga" ornamental pepper" Acta Horticulturae, 2005 (No. 683) 333-336] Seeds can be soaked with PBZ to reduce seedling growth. [Pasian and Bennett, "Paclobutrazol-Soaked Ornamental Kale Seeds Produce Short Seedlings" [http://ohioline.osu.edu/sc193/sc193_10.pdf] ] PBZ is the active component of Bonzi TM with 4g/l.

References