Morphological changes incitrus associated with relatively high concentrations of paclobutrazol

Progressively higher concentrations of Paclobutrazol-markedly reduced germination of Valencia sweet orange (Citrus sinensis (L.) Osbeck) seed and induced significant changes in the morphology, growth, and development of roots of Valencia seedlings and rough lemon (C. limon (L.) Burm. f.) leaves. Threshold concentrations for significant visible effect to radical change ranged from 10³ to 10⁵ ppm (2.84×10^–4 to 2.84×10^–2 M) (ai). Initial change was readily evident in reduced lateral and fibrous root development at the lower concentrations (10³ ppm). Higher concentrations (10⁵ ppm) resulted in no secondary root formation and progressive basal enlargement terminating in a bulbouslike apex of the primary root. Lack of secondary roots suggests disruption in the pericycle or severe inhibition of meristematic initial cells. Root system changes were not visibly indicated in shoot growth other than strong inhibition of extensions.Mention of a trademark, warranty, proprietary product, or vendor does not constitute a guarantee by the U.S. Department of Agriculture and does not imply USDA approval to the exclusion of other products or vendors that may also be suitable.