Effect of Plant Growth Regulators and Cold on Improvement of Morphological Characteristics of Cineraria (Pericallis × hybrida)

The climate of every region does not let to have year-round production of crops. Use of plant growth regulators allows to produce the flowers out of season and improve their quality and yield. Gibberellin is one of the plant growth regulators which can substitute cold requirement of plants, while cytokinin is another plant growth regulator to stimulate floral initials. Paclobutrazol is a triazole compound that inhibits gibberellin synthesis. Cineraria (Pericallis × hybrida) as a prominent flowering pot plant has a growing demand during the spring festivals especially Nowrouz, which needs further improvement of quality and yield. In this regard a study was designed to examine the morphological characteristics of cineraria using gibberellin, cytokinin, paclobutrazol and cold.
Seeds of cineraria (Pericallis × hybrida cv. Satellite( were sown in plug trays at the research greenhouse of college of agriculture, Shiraz University. A study was carried out with a completely randomized design and five replications. Control plants were transferred to incubators at eight leaves stage to receive six weeks of cold. Spraying treatments consisted of control (water), 100 mg/L gibberellin at three times (before cold, middle of cold and after cold), combinations of cold and/or gibberellin (100, 200 mg/L) with benzyl adenine (150, 300 mg/L) and/or paclobutrazol (250, 500 mg/L). In order to better understand the effects of paclobutrazol, its treatments were applied two weeks after gibberellin treatments. Data analysis was done by SAS 9.1 software and means were compared by LSD at 5 percent probability level.
Gibberellin can be used as a replacement for cold. The maximum acceleration of full flowering (32 days) and the greatest delay of full bloom (14 days) were observed in 100 mg/L gibberellin 250 mg/L paclobutrazol and 200 mg/L gibberellin 300 mg/L benzyl adenine, respectively. These results were consistent with other studies on iris, lily, tulip and hyacinth. The highest longevity of cineraria was observed in 100 mg/L gibberellin 250 mg/L paclobutrazol (31.8 days) which showed increasing of 24 days compared to control. Gibberellin and cytokinin lengthened the life of flowers, while paclobutrazol reduced the ethylene production and delayed the senescence. The greatest shoot fresh and dry weight was evaluated in 100 mg/L gibberellin 300 mg/L benzyl adenine, while paclobutrazol decreased the plant growth. Similar results have been reported in zinnia and geranium. Gibberellin and cytokinin increased leaf area, while paclobutrazol decreased it. The highest leaf area was detected using 100 mg/L gibberellin 300 mg/L benzyl adenine. . Maximum flower number was obtained using 100 mg/L gibberellin 300 mg/L benzyl adenine, while the lowest number was obtained by 100 mg/L gibberellin 500 mg/L paclobutrazol application. In addition, observations in orchid and jasmine were showed similar result. Gibberellin enhanced and paclobutrazol decreased plant height. plants Spraying with 200 mg/L gibberellin and cold 500 mg/L paclobutrazol showed the maximum and minimum height, respectively. Similar observations have been found in cyclamen and tuberose. number. . Also, Paclobutrazol application enlarged flower diameter. The greatest enhancement of flower diameter ( 1 cm) was found by cold 500 mg/L paclobutrazol spray. Flower diameter improvement is related to the severed growth, height and flower number by paclobutrazol. Flower diameter reduction in higher concentrations using gibberellin and cytokinin may be attributed to increasing translocation of carbohydrates to shoots and vegetative growth rather than flowers. Osteospermum and chrysanthemum showed similar and opposite results, respectively with this study. The effect of chemicals inhibitor depends on the number of applications, environmental conditions, plant sensitivity and how it is used. The bestvisual quality was detected in cold 150 mg/L benzyl adenine, 100 mg/L gibberellin 150 mg/L benzyl adenine and cold 500 mg/L paclobutrazol. Application of cold 500 mg/L paclobutrazol showed dwarf form, compact inflorescence and widened flower diameter. Additionally, minimumvisual quality was evaluated by cold 300 mg/L benzyl adenine which may be related to decreasing calcium uptake and subsequent lateral shoot bending.
Spraying with gibberellin, benzyl adenine and paclobutrazol had a positive effect on morphological traits of cineraria and increased its growth and development. Cineraria’s limited cultivation, due to its six weeks cold requirement, could be overcome by gibberellin application. Application of cold 500 mg/L paclobutrazol increased flowers and new compact form. Generally, 100 mg/L gibberellin 250 mg/L paclobutrazole spraying could reduce cineraria’s growth period for 32 days and make a new dwarf form. Overall, 100 mg/L gibberellin 300 mg/L benzyl adenine spraying reduced cineraria’s growth period for 21 days and also increased its fresh and dry weight, fresh root weight, leaf area, plant height, stem diameter, visual quality, flower number and flower longevity compared to other treatments.