The influence of growth regulators and nitrogenous compounds on in vitro bulblet formation and growth was studied in two hybrids of <i>Lilium</i>. Bulbscales isolated from pre-cooled bulbs of hybrids Rosato and Marco Polo were used. The basal portion with plate (5 &times; 6 mm) of inner bulbscales was cultured on Murashige and Skoog (MS) medium containing 0.5 or 1 mg/dm³ naphthaleneacetic acid (NAA) and/or benzyladenine (BA). The presence of NAA (0.5 mg per dm³) showed higher explant regeneration, producing about three bulblets per explant as compared to control. About four bulblets per explant were produced at both concentrations of BA. The bulblets with significantly higher fresh weight were obtained on medium containing NAA. Approximately a three-fold increase of bulblet fresh weight was observed with all the concentrations of TDZ in both cultivars. The bulblets cultured with nitrogenous compounds after attaining the size of 14&minus;16 cm flowered during the second year of the growing period without any phenotypic variations.

Gerbera has gained popularity in the past few years in many countries of the world and it is in great demand in the floral industry as cut flower as well as potted plant due to its beauty, colour, long vase life, and ability to rehydrate after long transportation. The most commercial cultivars are propagated through vegetative means by multiplication through divisions of clumps; however, the multiplication by this method is too slow to be commercially viable. To commercialize this crop and to meet the growing demand for planting material, tissue and organ culture techniques are being used as alternative methods for propagation in many countries. Most of the work has been carried on plant regeneration by adventitious organogenesis from capitulum, shoot tip, leaf, petiole and other parts of the plant. Attention should be paid to improve the technology to achieve 100% success in all species/cultivars to meet growing demands of the growers globally. From the literature, it is evident that gerberas are highly amenable to in vitro studies, as various explants were found to favourably respond to different culture media with different types and concentrations of growth regulators.

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Callus cultures derived from leaf segments of chrysanthemum cultivar 'Snow Ball' which was susceptible to Septoria obesa were successfully used for in vitro selection for resistance to this pathogenic fungus. Resistant cell lines were selected by culturing callus on growth medium containing various concentrations of S. obesa filtrate. Resistant calluses obtained after two cycles (30 d each cycle) of selection were used for plant regeneration. About 30% of the plants regenerated from the resistant calluses and 70-80% of the plants raised from cuttings had acquired considerable resistance against the pathogen in the field. No phenotypic variation was observed in the selected regenerates.

ABSTRACT:The influence of growth regulators, explants and their interactions on in vitro shoot bud formation from callus was studied in Dianthus caryophyllus L. The leaf and internode explants were cultured on Murashige and Skoog (MS) medium containing different concentrations of growth regulators. The highest callus induction was observed with 2 mg/l 2,4-dichlorophenoxy acetic acid (2,4-D) and 1 mg/l benzyl adenine (Ba). out of twenty seven shoot regeneration media tested, only 2 mg/l thidiazuron (tDZ) and zeatin alone or in combination with naphthalene acetic acid (Naa) and/or indole acetic acid (iaa) could differentiate calli. The highest average number of shoots was observed with 2 mg/l tDZ and 1 mg/l iaa. Significant differences were observed in calli producing shoots and number of shoots per callus in the explants of leaf and internode. The shoots were elongated and multiplied on MS medium supplemented with 1 mg/l Ba and solidified with 1% agar. The shoots were rooted and hardened with 76% survival success in pots after six weeks of transfer to the pots.