The response of three Leucadendron cultivars (Proteaceae) to phosphorus levels

Abstract The objective of this study was to compare the growth of three Leucadendrons (Proteaceae) cultivars (`Safari Sunset',`Orot' and`Meir') fertigated with three levels of P. The plants were grown in tuff (pyroclastic material, characterized by high porosity) in 10 l pots and fertigated daily. The experiment included control treatment (plants irrigated with tap water) and three levels of P (0, 10 and 20 mg l À1 ), while N and K in the P-treatments were kept at a constant rate of 50 mg l À1 . Under P de®ciency, the development of`Orot' plants was signi®cantly superior to that of`Safari Sunset' and`Meir' cultivars, but as P application increased to 20 mg l À1 ,`Safari Sunset' growth was quite similar to that of`Orot'. The very low growth rate of`Meir', probably eliminates this cultivar as a potential rootstock for commercial purpose. The low sensitivity of`Orot' to nutrient application is a promising characteristic to avoid micro-nutrients de®ciency and a signi®cant advantage, especially under ®eld conditions. No symptoms of P toxicity were observed even at the highest P level (20 mg l À1 ), at any of the cultivars tested.

Micrografting of Protea cynaroides

The inability to induce rooting of in vitro-established Protea cynaroides microshoots has prevented the production of complete plantlets. A successful shoot-tip micrografting technique was developed using in vitro-germinated P. cynaroides seedlings as rootstocks and axenic microshoots established from pot plants as microscions. Thirty-day old seedlings, germinated on growth-regulator-free, half-strength Murashige and Skoog medium, were decapitated and a vertical incision made from the top end. The bottom ends of microshoots established on modified Murashige and Skoog medium were cut into a wedge (‘V’) shape, and placed into the incision. The micrografted explants were cultured in a growth chamber with the temperature adjusted to 25 ± 2°C, with a 12-h photoperiod. Best results were obtained by placing the microscions directly onto the rootstock without any pre-treatments. Dipping the explants in anti-oxidant solution or placing a layer of medium around the graft area led to the blackening of the microscion. Abbreviations EDTA Ethylenediaminetetraacetate - BAP 6-Benzylaminopurine - GA3 Gibberellic acid - PAR Photosynthetic active radiatio