Highly Efficient Plant Regeneration System of Pot Calla Lily

Calla lily (Zantedeschia spp.), a genus of the Araceae family, is a perennial flowering plant and grows naturally in Middle and South Africa (Wei et al., 2017). This genus consists of two sections. The first group is Zantedeschia aethiopica that known as white calla lily and has a rhizomatous storage organ and is an evergreen. The second group is colored calla lilies and they have tuberous storage organ and require a period of dormancy (Zhang et al., 2011). Calla lilies are commercially available as cut flowers and potted plants. These flowers have high commercial value in the market due to their attractive inflorescence (Jonytiene et al., 2017). According to the 2014 statistics, turnover of calla lily was 19 million € (euro) in Netherlands (Floraholland facts and figures, 2014). It contributed to a substantial proportion of horticultural export earnings in the Netherlands and America. The colored calla lily tuber yield in these two countries has significantly increased in recent years to supply foreign market demands especially in Asia (Wei et al., 2017). In most cases, conventional propagation of calla lily is dividing the tuber, but this method requires to the high-skills and causes the development of the root soft rot disease as well. Bacterial soft rot disease caused by Erwinia carotovora subsp.

Carotovora is a major problem in Zantedeschia spp. Infection occurs at all stages of the life cycle from growing time of the plants in the field to tubers in store and it spreads quickly in calla lily (Wright et al., 2002). The final stage is destruction of the plant and death; losses can approach 100% in a severe outbreak. For a long time, this disease has been recognized as a major cause and fatal disease which the calla industry has not progressed (Cho et al., 2013). It should be noted that the acquisition of vigorous plants is considered indispensable for the satisfactory flower production. The knowledge and application of principles and techniques from the choice of the propagation material until the management of the seedlings are necessary to produce high-quality plants (Oliveira, 2007). Therefore, growers are looking for a way to reduce problems and production of high-quality plants in calla lily. The use of in vitro culture methods can be effective in reducing losses and increasing the quality (Cheng et al., 2003). Propagation via tissue culture is the most suitable method to obtain numerous pathogen-free plants rapidly (Kulpa, 2016). Actually, micropropagation is widely used for commercial purposes as a method of vegetative propagation from different explants.

The successful use of tissue culture techniques has been announced in several reports for rapid propagation of the genus Zantedeschia. Chang et al (2003) presented a method for the micropropagation of Zantedeschia albomaculata by using shoot tip proliferation. Results showed that 6-benzyladenine (BA) and thidiazuron (TDZ) were found to be more effective and optimal concentration of BA or TDZ were 8.87 mM and 4.54 mM, respectively. Koech et al (2005) described a protocol for in vitro shoot regeneration of Zantedeschia albomaculata, by using shoot primordium explants. Shoot explants can be used to produce high-quality multiple shoots, by using MS medium supplemented with 2.0 mg L-1 BAP. In their experiment, no response was observed in both leaf and tuber explants. Duquenne et al (2006) explained that the induction of direct somatic embryogenesis in Zantedeschia hybrids was obtained on media supplemented with 2.0 mg L–1 NAA and 0.6 to 2.0 mg L–1 BA.

Gliozeris and Tamosiunas (2008) reported that transfer of Zantedeschia cv. Ruby plantlets from MS medium containing 0.3 mg L-1 BAP to the medium containing various NAA concentrations stimulated growth of shoots. Sanchez et al (2011) examined shoot propagation of Zantedeschia spp in a temporary immersion system. Kulpa (2016) reported that the highest shoot length (3.41 cm) and the number of adventitious shoots (4.13) were obtained on the MS medium supplemented with 2.5 mgdm-3 BAP in Zantedeschia rehmannii. Due to the high sensitivity of this plant to the disease, the development of resistant cultivars is the main purpose in overcoming problems caused by soft rot. But the lack of a complete regeneration protocol of calla lily has caused limitations on the use of new technologies for the improvement of this crop. Because the introduction of transgenes into the genome of plant species require successful regeneration of plantlets from cells (Hill and Schaller, 2013).

According to our information, there is only one report about gene transformation in calla lily so far. Yip et al (2007) could not produce callus and they were used of direct regeneration in Zantedeschia elliottiana ‘Florex Gold’. In this report, shoot basal tissue from shoot cultures with a diameter of more than 4 mm was used as explants. It seems regeneration in calla lily is challenging, and mechanisms required for in vitro regeneration have been insufficient so far. The objective of this study was to develop an efficient micropropagation and regeneration protocol for Zantedeschia plants. To the best of our knowledge, the present study is the first report to demonstrate the high efficient indirect regeneration of colored calla lily. This protocol could be used to overcome the in vitro mutation breeding and genetic engineering barriers.