Growth and morphogenesis of Protea cynaroides L. explants in vitro are relatively slow. Besides being essential for photosynthesis, light quality also plays an important role in plant morphogenesis. In this study, the effects of light quality on the growth of P. cynaroides apical shoots cultured under light-emitting diodes (LEDs) were investigated. Three light treatments were used: conventional cool white fluorescent lamps (FL) (control), far-red (FR) LEDs (770 nm), and red + far-red (R+ FR) (1:1 spectral energy) LEDs (640 + 770 nm). Two types of growth media were used: half-strength Murashige and Skoog (MS) medium upplemented with either 0.1 mg L⁻¹ naphthalene acetic acid (NAA) or 2 mg L⁻¹ zeatin and 0.5 mg L⁻¹ indole-3- acetic acid (IAA). After 35 days in culture, chlorophyll content (SPAD value) of apical shoots was lowest in explants cultured in growth medium containing 2 mg L⁻¹ zeatin and 0.5 mg L⁻¹ IAA, and irradiated by FR LEDs. Significantly higher chlorophyll content was detected in explants cultured under R + FR LEDs on medium containing 0.1 mg L⁻¹ NAA, which was similar to those grown on medium containing 2 mg L⁻¹ zeatin and 0.5 mg L⁻¹ IAA under white fluorescent lamps. Under white light, the bud weight of apical buds cultured on media supplemented with 2 mg L⁻¹ zeatin and 0.5 mg L⁻¹ IAA was significantly higher than the other treatments. The highest number of buds was observed on shoots irradiated by white light and R+ FR LEDs, cultured on media containing 2 mg L⁻¹ zeatin and 0.5 mg L⁻¹, and 0.1 mg L⁻¹ NAA, respectively. Explants irradiated by FR LEDs on medium containing 0.1 mg L⁻¹ NAA produced the least number of buds. Results suggest that irradiation of P. cynaroides explants by LEDs containing red light induces the growth of new buds in the absence of zeatin.
