In vitro multiplication of Protea cynaroides L. microshoots and the effects of high phosphorous concentration on explant growth

Protea cynaroides L. is a slow-growing, difficult-to-propagate plant. Due to problems such as phenolic browning and their sensitivity to the phosphorous nutrient, in vitro multiplication of P. cynaroides explants have not been successful. The present study was conducted to induce shoot proliferation of established P. cynaroides microshoots, and investigate the effects of high phosphorous concentration during explant multiplication. Microshoots with either one or two nodes were cultured on Murashige and Skoog (MS) medium containing modified macro nutrients and full strength micronutrients. Two concentrations of NH sub(4)H sub(2)PO sub(4) were tested: 0 mg L super(-1) NH sub(4)H sub(2)PO sub(4), and a high P concentration of 1400 mg L super(-1) NH sub(4)H sub(2)PO sub(4). Both growth media were also supplemented with gibberellic acid (GA sub(3)) (30 mg L super(-1)), 6-benzylaminopurine (BAP) (2: mg L super(-1)), ethylenediaminetetraacetic acid (EDTA) (50 mg L super(-1)) and indole-butyric acid (IBA) (0.5 mg L super(-1)). Results show that, contrary to what is often reported, the presence of a high phosphorous concentration in the growth media did not adversely affect P. cynaroides explants. The survival rate and mean axillary shoot length of explants cultured on growth media containing 1400 mg L super(-1) NH sub(4)H sub(2)PO sub(4) were not significantly different from those grown on 0 mg L super(-1) NH sub(4)H sub(2)PO sub(4). No phosphorous toxicity symptoms were observed in explants cultured on media with high phosphorous levels. Results also show that explants with two nodes had a higher survival rate and produced significantly longer axillary shoots than those with one node, irrespective of phosphorous concentration. Multiplication of P. cynaroides microshoots was successfully achieved for the first time.