Carnation, a high value commercial cut flower crop, is cultivated in India both for domestic and export market. In our study, we aimed at increasing the multiplication of microshoots for supplying quality planting material to farmers. This paper reports the effect of various growth regulators on maximizing the production of quality microshoots measuring 2-4 cm length, which is found to be efficient in rooting and field establishment. The supplementation of GA3 was found to be essential for maximizing the regeneration of microshoots. A comparative study between the effect of BA and Kinetin indicated that BA had positive impact on number of leaves per explant and total number of microshoots regenerated. Addition of BA at 1 ppm maximized the production of number of desired microshoots (2-4 cm). The media supplemented with combination of GA3 (0.25 ppm), BA (1 ppm) and NAA (0.25 ppm) was found to be the best for production of quality microshoots.

Carnation (Dianthus caryophyllus L.) is a commercially important cut flower crop grown under protected cultivation. Quality planting material is a prerequisite for efficient production of carnation flowers. Being a high density crop, requirement of planting material in carnation is in huge demand, needing 10-15 thousand plants per acre. At present, tip cuttings are used for multiplication and production of planting material for commercial cultivation. Production of planting material is limited by the mother plants that need to be maintained under protected condition. Tissue culture is considered as an alternate strategy for propagation of planting material in large scale (Kiss et al., 2001). Carnation is easily amenable for micropropagation (Ajitabh et al., 2006; and Meena Wankhade et al., 2006). Efforts were made for utilizing micropropagation techniques in carnation as a tool in carnation breeding program (El Sharnouby and El Khateeb, 2005; and Tejaswini et al., 2005 and 2006).

Combining the advantage of tissue culture and capacity of vegetative propagation, an alternate strategy was worked out that includes the mass production of microshoots by tissue culture and rooting them under ex vitro condition. In this alternate strategy, microshoots produced under tissue culture served as shoot tip cuttings which will be subjected to ex vitro rooting. In our carnation breeding program, utilizing tissue culture as a tool, media composition of 6-Benzyl Adenine (BA), Gibberellic acid (GA3) and Ü-Naphthalene Acetic Acid (NAA), each at 0.25 ppm had given good regeneration (Tejaswini et al., 2005 and 2006). However, the major problem we faced was elongated microshoots having problem with establishment and field growth. Exploratory studies conducted in our laboratory indicated the efficiency of microshoots of 2-4 cm length in rooting and field establishment. Hence, the present study was taken up to maximize the regeneration of microshoots of 2-4 cm length. Our experimentation dealt with altering the level of growth regulators. We tried to experiment with removal of GA3 from the media, followed by altering the type and concentration of cytokinins. BA and Kinetin were the two forms of cytokinins used in the experiment.

Gibberellic acid is reported to promote elongation of the microshoots (Satoko et al., 2008). In the light grown hypocotyls, exogenous GA3 represses the extent of thickening and promotes cell elongation by wall thinning (Derbyshire et al., 2007). Our objective is to produce microshoots that are neither thin nor elongated and hence we experimented to initiate cultures devoid of GA3 in the media. There are also reports on culturing of carnation on media devoid of GA3 (Lubomski and Jerzy, 1989). Cytokinins are responsible for multiplication of cells and in turn are expected to enhance the number of microshoots. Lubomski and Jerzy (1989) reported the best shoot formation response of carnation on MS medium supplemented with BA. However, Mangal et al. (2002) and Onamu et al. (2003) reported usage of Kinetin for shoot induction from meristem. Higher concentration of BA (1-3 ppm) was reported to maximize the number of microshoots produced under in vitro (El Sharnouby and El Khateeb, 2005; and Aamir et al., 2008). In this study, we aimed at finding out the suitable form and concentration of cytokinin for maximizing the production of microshoots of desirable length.

Biotechnology Journal, Stress Adaptation of Bacteria, Extremophiles, Bacterial Adaptation, Cytosolic Components, Denature Cellular Proteins, Reactive Oxygen Species, Monounsaturated Fatty Acids, Ultraviolet Radiation, Environmental Stress, Stress Management, Biological Systems, Cellular Economy.