The Influence of Paclobutrozol, a New Growth Regulator, on Sunflowers1

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Abstract
Paclobutrozol PP333 = (2R,3R + 2S,3S)-1-(4-chlorophenyl)-4,4-dimethyl-2-(1,2,4-triazol-1-yl) pentan-3-ol at concentrations of 11.6, 58.0, and 116.0 mg of active ingredient per liter caused significant reductions in water use of sunflowers (Helianthus annuus L.) but there was no significant influence on leaf diffusive resistance. The primary mechanism for reduced water use is by a reduction in leaf expansion. PP333 inhibited internode elongation which causes increased leaf shading. Under nonstress conditions there was no effect on leaf water potential or its components. At the highest concentration, photosynthetic rate was reduced. Fresh and dry weight of shoots was reduced proportional to leaf area. Gibberellic acid reversed the effect of PP333 of shoot height, leaf area, evapotranspiration, and shoot fresh and dry weight.

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