Aims: A two-year field trials were carried out during the two successive seasons of 2015 and 2016 to study the effect of pinching and paclobutrazol (PP333) at 20, 40 and 60 ppm on growth, flowering, histological characteristics and chemical compositions of potted Pelargonium zonale L. plant .
Methodology: Uniform terminal cuttings were planted in 8 cm plastic pots containing 1:1 mixture of peat moss and sand. On March 1st of 2015 and 2016, uniform well rooted cuttings were repotted in 20cm diameter plastic pots filled with a mixture of 1 clay: 1 sand :1 peat moss (v:v:v). Pinching was applied after 21 days from transplanting by removing the apical bud of all the upcoming buds, allowed to produce side shoots. After one month, the plants were received four sprays with PP333 at 20, 40 and 60 ppm plus tap water as control at two weeks intervals.
Results: Results showed that: All pinching and PP333 concentrations decreased plant height (compacting showy plants), particularly the combined treatment of PP333 at 60 ppm with pinching in both seasons. On the other hand, all applied treatments of pinching and PP333 statistically increased number of branches / plant and stem diameter/(cm) to reach its maximum with the highest concentration for each. The heaviest fresh and dry weights of leaves/plant, the highest number of leaves/ plant, the highest number of flowers/ plant whereas the heaviest flowers fresh and dry weights/plant were gained from plants pinched and sprayed by PP333 at 60 ppm in the two seasons. In addition, all different applied treatments of pinching and PP333 statistically decreased leaf area / (cm2) as compared with control plants (without pinching) which induced the largest leaf area / (cm2) and the earliest flowers in the first and the second seasons. Moreover, the highest show value (plant width/ height ratio) was recorded by the interaction treatments of pinching and PP333 at the highest concentration in both seasons. The highest number of roots/plant and the heaviest fresh and dry weights as well as leaf N, P, K, total carbohydrates, total chlorophylls contents and leaf total phenols content gave the significantly highest mean value for the interaction treatment of pinching and 60 ppm PP333 -sprayed plants in the two seasons. All pinching and PP333 treatments increased leaf total phenols content (mg/100g F.W), but they reduced total indoles (mg/100g F.W) of Pelargonium zonale L. Leaves. Moreover, the interaction of PP333 at 40 ppm with pinching or PP333 at 60 ppm without pinching recorded highly significant increments of all above mention parameters in the first and the second seasons. Furthermore, the obtained results indicated that all PP333with and without pinching treatments increased cytokinins and salicylic acid contents, but they decreased gibberellins, auxins and abscisic acid (mg/100g F.W) of Pelargonium zonale L. shoot with superiority of PP333 at 60 ppm with pinching compared with control and other used treatments. Regarding to the anatomical features of leaf and stem anatomy, most traits were increased with different applied treatments compared with the control, particularly pinching with PP333 at 60 ppm treatment. Consequently, it is preferable, to obtain a good display of flowering pot of Pelargonium zonale L. plants with formative growth and flowering characteristics from the commercial point of view, treating geranium plants with PP333 at 60 ppm applied as spray supported with pinching treatment practice four times a year.
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