Genetic improvement of ornamental geophytes especially the monocotyledonous type; is often restricted by failure of Agrobacterium to reach competent cells as well as a lack of efficient regeneration systems. Despite all these limitations, it has recently been shown that the use of efficient promoters, super-virulent strains, and the utilization of systems such as an agrobacterial monolayer, Agrobacterium-mediated pollen and seed transformation, floral dip method and sonication-assisted Agrobacterium-mediated transformation (SAAT) will ensure success in the genetic transformation of these ornamentals in the near future. This article outlines factors affecting transformation of monocotyledonous geophytes. Special emphasis is laid on measures that have been employed to alleviate various difficulties. The need to develop somatic embryogenesis protocols for the ease of transformation is highlighted. In addition, perspectives in view of future research are also given. This information is crucial for biotechnological improvement of ornamental geophytes that are proving difficult to transform.

The genus Dierama comprises plants with a potential to be developed as ornamentals. D. erectum seeds were decontaminated and germinated on 1/10th strength Murashige and Skoog (Physiol Plant 15:473-497, 1962) (MS) media without plant growth regulators or sucrose. In an experiment investigating the effects of 6-benzyladenine (BA), meta-Topolin (mT), kinetin (KIN) and zeatin (Z) with or without a-naphthaleneacetic acid (NAA), the highest shoot number per hypocotyl (4.20 ± 0.51) was obtained from MS medium supplemented with 1.0 lM Z after 8 weeks. This was followed by a combination of 2.0 lM KIN and 2.0 lM NAA with 3.67 ± 0.81 shoots per explant. BA treatments produced 3.20 ± 0.22 shoots per hypocotyl explant when 2.0 lM was combined with 1.0 lM NAA, while mT gave 3.09 ± 0.99 shoots per explant when 2.0 lM mT was combined with 2.0 lM NAA. Adventitious shoot regeneration was optimised when shoots were grown under a 16-h photoperiod at 100 lmol m -2 s -1 on MS medium supplemented with 1.0 lM BA. This resulted in an average of 12.73 ± 1.03 shoots per hypocotyl explant. Various concentrations of ancymidol, activated charcoal and sucrose did not promote in vitro corm formation of this species. Plants rooted successfully after 8 weeks on MS medium supplemented with 1.0 lM indole-3-butyric acid (IBA) and had an average root number of 2.73 ± 0.40. After 2 months of acclimatisation, plants had formed corms. The largest corms (of diameter 0.45 ± 0.03 cm) were produced in plants pre-treated with 0.5 lM IBA. The highest plant survival percentage of 73% was also associated with this treatment.

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