Abstract
Poor and inconsistent germination of Protea cynaroides seeds are often observed in soil. A protocol based on embryo culture was developed for efficient in vitropropagation of P. cynaroides. The effects of temperature, light conditions and gibberellic acid (GA3) on the in vitro germination of P. cynaroides embryos were studied. The results showed that the use of alternating temperatures of 21/12°C (light/dark) significantly improved the germination percentage of the embryos, where 90% of embryos germinated, compared to a maximum of 55% when grown under a constant temperature of 25°C. Mean cotyledon fresh mass of embryos that germinated on media containing gibberellic acid (2.89, 28.89 μM GA3) were significantly higher than those cultured on media without growth regulators. Conversely, root growth was severely inhibited in embryos germinated on media containing gibberellic acid. The in vitro-germinated seedlings were successfully transplanted to a peat/coir/sand mixture in the mist bed. Key words: Alternating temperature, embryo culture, gibberellic acid, King Protea, Proteaceae.
Highlights
Protea cynaroides (King Protea) is endemic to South Africa
The largest difference in germination percentage was observed under the 12 h photoperiod on basal 1⁄2 Murashige and Skoog (MS) medium without Gibberellic acid (GA3), where 90% of embryos germinated under the 21/12°C temperature regime compared to only 20% under 25°C
With regard to the media treatments, in the 21/12°C temperature regime, no significant differences were found in the germination percentage between the basal 1⁄2 MS medium and those supplemented with GA3, irrespective of whether it was under the 12 h photoperiod or continuous darkness (Figure 2)
Summary
Protea cynaroides (King Protea) is endemic to South Africa. It is an important cut flower in the floriculture industry. Seeds are used by Protea growers to obtain new plants. Seed propagation of members of the Proteaceae are known to be difficult. This is because Proteaceae seeds germinate poorly and erratically (Deall and Brown, 1981). Germination usually takes a long period of time. Several studies have shown that endogenous inhibitors contribute to poor germination of Proteaceae seeds; Brown and van Staden (1971) showed that inhibitors found in aqueous seed extracts of Protea compacta, Protea barbigera, Leucospermum
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