Paclobutrazol Affects Growth and Flower Bud Production in Gardenia under Different Light Regimes

The effects of several shading materials on the response of Gardenia jasminoides Ellis to paclobutrazol were investigated under greenhouse conditions. The three main plot treatments were shading (0%, 67%, 98%), and paclobutrazol (0.0, 0.5, 1.0, and 2 mg/pot) was applied as a soil drench in each main plot after pinching the plants. Both plant size and the number of flower buds per plant decreased as the rate of paclobutrazol increased at all levels of shading. The efficacy of paclobutrazol, however, was generally less under heavy shade, as both translocation of the growth retardant and photosynthesis were reduced. Moderate shading (67%) did not affect the size of plants receiving 0.0 or 0.5 mg of paclobutrazol per pot, but plants grown under heavy shade (98%) were 74% as large as similarly treated nonshaded plants. Medium shade reduced the size of plants receiving 1 and 2 mg paclobutrazol 4% and 6%, respectively, relative to that of similarly treated nonshaded plants, whereas heavy shade reduced plant size 11%. The number of flower buds per plant was reduced 30% by moderate shading, 90% by heavy shading. Significant quadratic relationships were observed between the rate of paclobutrazol applied and (1) plant size, and (2) the number of flower buds per plant. Chemical name used: ±-( R * ,R * )-β–[(4-chlorophenyl)methyl]-α-(1,1-dimethyl)-1 H -(1,2,4-triazol)-1-ethanol (paclobutrazol).