Russell D. Caldwell

Gibberellic acid affects growth and flowering of Philodendron 'Black Cardinal'

A single foliar spray of gibberellic acid (GA3) at concentrations of 125, 250, 500, or 1,000 mg L−1 induced flowering of Philodendron‘Black Cardinal’ (an interspecific hybrid developed from a series of crosses among P. wendlandii, hastatum, erubescens, imbe, fragrantissimum, and an unnamed species) in approximately 170 d. Percentage of plants induced and mean flower number per plant increased as GA3 concentrations increased. Compared to unsprayed plants, the number of new leaves decreased, petiole lengths of new leaves and length of the largest leaf increased, but leaf width was unaffected among sprayed plants. One hour before the spathe started to unfurl, spadix temperatures increased, and temperatures in the male portion of the spadix rose by 10 °C above ambient as the spathe fully opened. Elevated temperatures were recorded for about two hours and returned to ambient within five hours. Spathes remained open for about five hours. A creamy white spadix with a contrasting burgundy spathe resulted in more aesthetically pleasing plants than with foliage alone. Because of the short period of display, the open spathe would not increase additional ornamental value of Philodendron‘Black Cardinal’ in the marketplace. However, if breeding is the purpose of flowering induction, spathes should be cut away from the spadix to facilitate pollination.

Production and Interior Performances of Tropical Ornamental Foliage Plants Grown in Container Substrates Amended with Composts

Three representative Florida composts were mixed by volume with sphagnum peat and pine bark to formulate 12 container substrates. After physical and chemical characterization, the substrates, along with a control, were used to grow containerized Cordyline terminalis ‘Baby Doll’, Dieffenbachia maculata ‘Camille’, and Dracaena fragans ‘Massangeana’ cane. All substrates were able to produce marketable plants, but only five or seven, depending on plant genus, of the 12 compost-formulated substrates resulted in plants comparable or superior to those of the control substrate. The five also had substrate shrinkage equal to or less than the control. Plants were then moved to an interior evaluation site to determine the suitability of compost-formulated substrates in sustaining foliage plant growth under an interior environment. During a six-month interior evaluation, the plants maintained their aesthetic appearances. Based on plant growth parameters and quality ratings as well as substrate shrinkage both in production and interior evaluation, five of 12 compost-formulated substrates were identified to be equal or superior to the control. This study showed that the three composts, after being appropriately mixed with sphagnum peat and pine bark, can be used as container substrates in every phase of tropical foliage plant production and utilization.

Thidiazuron promotes adventitious shoot regeneration from pothos (Epipremnum aureum) leaf and petiole explants

SummaryRegeneration of adventitious shoots of pothos (Epipremnum aureum Linden and Andre) ‘Jade’ was obtained using leaf and petiole explants preprated from shoot tips of 3-yr-old greenhouse-grown plants. Explants were cultured on Murashige and Skoog (MS) basal medium supplemented with thidiazuron (TDZ), 6-(4-hydroxy-3-methy-trans-2-butenyl-amino)purine (zeatin) or N-isopentenylaminopurine (2iP) individually with α-naphthaleneacetic acid (NAA) in 18 combinations. Callus was initiated from cut surface and along the midrib or major vein of leaf sections. Shoot regeneration from leaf and petoole explants occurred in 30d on medium containing 1, 5 or 10μM TDZ with 0.5 or 1.0μM NAA except petioles on medium with 10 μM TDZ and 1.0 μM NAA where regeneration failed. More time (50d) was needed for shoot regeneration when explants were cultured on medium containing either 2iP or zeatin with NAA. Regeneration frequencies were up to 20% and 50% for leaf and petiole explants, respectively. Shoot numbers per responding explant attained 30 for leaf and petiole explants on medium containing TDZ but only one to four on medium containing either 2iP or zeatin. These results indicate that TDZ is a more effective cytokinin for in vitro regeneration of pothos than either zeatin or 2iP.. Shoots elongated readily and rooted well on MS basal medium, without plant growth regulators. Plantlets acclimatized rapidly and grew vigorously in the greenhouse after transfer to pots containing a commerecial potting medium.

Best Management Practices for Minimizing Nitrate Leaching from Container-Grown Nurseries

Containerized plant production represents an extremely intensive agricultural practice; 40,000 to 300,000 containers may occupy one acre of surface area to which a large amount of chemical fertilizer is applied. Currently, recommended fertilizer application rates for the production of containerized nursery ornamental plants are in excess of plant requirements, and up to 50% of the applied fertilizers may run off or be leached from containers. Among the nutrients leached or allowed to runoff, nitrogen (N) is the most abundant and is of major concern as the source of ground and surface water pollution. In this report, current N fertilizer application rates for different container-grown nursery ornamental plants, the amount of nitrate leaching or runoff from containers, and the potential for nitrate contamination of ground and surface water are discussed. In contrast, our best N management practices include: (1) applying fertilizers based on plant species need; (2) improving potting mediums nutrient holding capacity using obscure mineral additives; (3) using controlled-release fertilizers; and (4) implementing zero runoff irrigation or fertigation delivery systems that significantly reduce nitrate leaching or runoff in containerized plant production and encourage dramatic changes in N management.