Effect of different Genotypes, Cytokinins and Auxins on In vitro Capitulum Regeneration of Gerbera (Gerbera jamesonii)

Gerbera is one of the most important ornamental plants in the world. The importance of Gerbera is due to its beauty, diversity and economically aspects. Traditional propagation methods such as crown division and cutting methods are not suitable for obtaining disease free plants and rapid multiplication. These methods also do not have the capacity to fulfill global demands. Therefore, obtaining efficient protocol for micropropagation of this ornamental plant is necessary.
In this study the effect of various factors on in vitro regeneration, proliferation, rooting and acclimation of gerbera capitulum explants were analyzed in four separate experiments. Capitulum explants were first washed with running tap water for 30 min then surface sterilized by dipping in 1.5% sodium hypochlorite solution for 15 min and rinsed with sterile distilled water, followed by immersing in 0.1 % mercuric chloride solution for 10 min. To remove mercuric chloride residue, capitulum was rinsed with sterile distilled water. Subsequent washing was done with sterile distilled water for three times. Sterilization steps were done under laminar air flow hood. For regeneration, eight genotypes of gerbera capitulum explants (Famous, Sunway, Red Pearl, Pink Snow, Popov, Balance, Dune, Eagle)were cultured on solid MS medium containing several cytokynins, BA, TDZ, 2IP or KIN (4 mg/l) in combination with IAA (0.2 mg/l). In proliferation stage, the effect of different concentrations of BA was evaluated on proliferation rate of Sunway regenerated explants. In the rooting stage, Sunway genotype plantlets were cultured on ½ MS medium containing NAA, IBA or IAA (1 mg/l) or ½ MS medium without any hormones. The pH of the medium was adjusted to 5.7-5.8 prior to autoclaving (15 min at 121 oC and 1.5 kg.cm-2 pressure). The cultures were incubated in a growth chamber at 25±2 oC with a 16-h photoperiod (2500-3000 Lux) provided by cool-white fluorescent lamps. For acclimation of rooted plantlets, different substrates used as follow: 1- perlite, 2- perlite: Cocopeat, 3- Cocopeat: peat moss, 4- Cocopeat: peat moss; treated with fungicide.
After 30 days, the response of explants was evaluated for each experiment. Data preparation was done in the Excel program and data analysis was done using JMP-8 software. Mean comparison of the treatments was done by Tukey test and finally the charts were drawn using the Excel program.
The results of regeneration stage showed that application of MS media containing kinetin or 2IP did not make an appropriate response to capitulum explants and no regeneration was observed in this condition. The medium containing 4 mg/l BA and 0.2 mg/l IAA indicated the highest percentage of regeneration in all genotypes. The highest regeneration was observed in Sunway genotype with an average of 21.96%. On the other hand no regeneration was observed in Eagle genotype. In terms of the number of regenerated plantlet, the highest number (61.2) was attributed to the Sunway genotype while no plantlet was recorded for Eagle genotype. No significant differences were also observed between Pink Snow and Dune genotypes. For the proliferation stage, only Sunway genotype was utilized due to its vigorous growth in comparison to other genotypes. In this stage, the highest (6 regenerated plantlets) and the lowest (1 regenerated plantlet) regeneration rate were observed in MS medium containing 2 mg/l BA and hormone-free medium, respectively. Hormone-free ½ MS medium and ½ MS medium containing 1 mg/l IAA or IBA, indicated the highest rooting rate (100% rooting) while medium containing 1 mg/l NAA showed 55% rooting rate. It seems that the application of NAA in the medium composition had the lowestimpact on the rooting of regenerated plantlets. At the end of the experiment, the highest (90.42%) and the lowest (47.5%) acclimation rate was obtained in peat moss cocopeat fungicide medium and perlite medium, respectively.
Generally, for shoot induction of gerbera through capitulum culture, application of MS medium containing 4 mg/l BA and 0.2 mg/l IAA is recommended. It is also concluded that for proliferation stage, the MS medium containing 2 mg/l BA showed the highest rate of regeneration. Using of Hormone-free ½ MS medium is economically affordable. Finally for acclimation of the plantlets, application of peat moss cocopeat fungicide medium is recommended.