The influence of medium aeration on in vitro rooting of Australian plant microcuttings

Media with different air filled porosity were compared with standard agar medium for root induction and root elongation for two Australian plants Grevillea thelemanniana and Verticordia plumosa X Chamelaucium uncinatum. Microcuttings from shoot cultures were pulsed for 7 days on a high auxin (40 muM IBA), agar-solidified medium in the dark. The rooting of the microcuttings was then compared on standard agar medium (M1, 1/2 MS, no hormones) and on three experimental treatments: porous-agar medium (1/2 MS, no hormones, 30 g agar l(-1), solidified then blended to provide aeration) white sand, or white sand wet with M1 medium; and a sterile propagation mix. The protocol using the propagation mix is referred to as IVS (In Vitro Soil). A separate experiment involved flushing the IVS soil profile with low or normal oxygen. The controls on M1 medium showed low and variable rooting percentages. The rate of root induction and the average total root length per microcutting at final harvest was significantly higher using the IVS protocol, porous-agar or white sand, while addition of agar medium to sand suppressed the percentage rooting and elongation as did flushing the air space in the IVS rooting medium with low oxygen. Other species tested on M1 medium and IVS including Pimelea physodes, Conospermum eatoniae, Verticordia grandis, and a Chamelaucium megalopetalum X C. uncinatum hybrid all showed a significant improvement on the IVS system. The IVS culture technique reduces plant-handling costs.