Impatiens ‘New Guinea’ (Impatiens hawkeri Bull) Hormonal Effects during the Post-transplant Biomass Accumulation

Pot ornamental plant productivity is related to the environmental growth facilities but negatively affected by the pot root restriction syndrome so during nursery as the post-transplant stage. The physiological mechanism involved included both the synthesis and translocation of auxins and cytokinins. However, clear sink-source and dose-response relationships of exogenous plant regulators such as indole acetic acid (AIA) and benzyl amino purine (BAP) and environment on biomass accumulation in most ornamental foliage plants, including New Guinea Impatiens (Impatiens hawkeri) are lacking. The aim of this work was to analyze the effects of an exogenously shoot-applied auxin and a cytokinin, separately or successively, on the post-transplant biomass accumulation of I. hawkeri through the anatomical, morphological and physiological changes observed. Two experiments were performed. The first experiment included the response to only BAP-sprayed plants (0, 5, 50, or 100 mg L-1). For the second experiment, rooting cuttings of I. hawkeri were sprayed with different concentrations of IAA (0, 5, 50, or 100 mg L-1) followed by different BAP concentrations (0, 5, 50, or 100 mg L-1) one week later to run-off at sunset. Results showed that (a) a single BAP or AIA dose increased increase post-transplant biomass accumulation through a higher leaf area expansion and photo assimilate production, (b) as a result of both AIA and BAP spray, the higher NAR the higher post-transplant biomass accumulation, (c) leaf anatomical changes (leaf thickness, intercellular spaces) let a higher carbon dioxide diffusion and fixation with a correlative increase in photo assimilates, (d) a higher root system would be related to a higher cytokinin synthesis. In summary, similarities between responses to either hormone, together with the lack of any IAA - BAP interaction, provide two independent routes for commercial growers to increase the productivity of I. hawkeri ornamental plants by using early foliar sprays.

Daily Evapotranspiration of Guzmania ‘Irene’ and Vriesea ‘Carly’ Bromeliads Produced in a Shaded Greenhouse

Bromeliads are important ornamental foliage plants, but until now, their daily water use during production was unknown. Using a canopy closure model developed for container-grown woody ornamental plants, in this study we investigated actual evapotranspiration (ETA) of Guzmania ‘Irene’ and Vriesea ‘Carly’ from tissue-cultured liners grown in 15-cm containers to marketable sizes in a shaded greenhouse. The mean daily ETA of Guzmania ‘Irene’ ranged from 4.02 to 66.35 mL per plant, and the mean cumulative ETA was 16.66 L over a 95-week production period. The mean daily ETA of Vriesea ‘Carly’ varied from 3.98 to 59.89 mL per plant, and the mean cumulative ETA was 15.52 L over the same production period as the Guzmania cultivar. The best-fit models for predicting daily ETA of the two bromeliads were developed, which had correlation coefficients (r2) of 0.79 for Guzmania ‘Irene’ and 0.68 for Vriesea ‘Carly’. The success in the model of ETA for both bromeliads suggested that the canopy closure model was equally applicable to container-grown ornamental foliage plants produced in greenhouse conditions. The daily ETA and cumulative ETA values represent research-based information on water requirements, and, when applied, could improve irrigation practices in bromeliad production. This study also showed that roots per se of the two epiphytic bromeliads were able to absorb water and nutrients from a peat-based container substrate and support their complete life cycles.

Water-based Cold Protection of Chill-sensitive Foliage Plants in Shadehouses

Four water-based cold protection systems [under-benches mist (UBM), over-roadways mist (ORM), and two among-plants fog (APF1, APF2)] were evaluated for their water use and effectiveness in protecting ornamental foliage plants from chilling injury (CI) under protected shade structures at three commercial locations in Florida. UBM used a two-stage thermostat-controlled system with mist nozzles on 25-cm above-ground risers combined with an overhead retractable heat curtain. Both ORM and APF1 had seasonally applied polyethylene film cladding and manually controlled irrigation systems. The ORM system had the mist nozzles located 1.8 m high and APF1 and APF2 systems had the low-pressure fog nozzles mounted on 25-cm above-ground risers spaced among the plants. Temperature data loggers were placed outside and inside the northwest sections of the shadehouses. ORM and the two APF systems were evaluated during freeze events in 2006, 2007, and 2008 and UBM only in 2007 and 2008. UBM, ORM, and APF1 successfully kept the shadehouse temperatures above critical chilling temperatures for all of the foliage plants. APF2 protected all foliage crops except for jungle drum “palm” (Carludovica sp.) that sustained CI. At the UBM site, the air temperatures recorded inside the shadehouse were ≈17 °C warmer than outside. Both ORM and APF1 maintained adequately warm temperatures inside the shadehouses; however, the fog system maintained equal or higher temperatures than the mist system and used 86% less water. Inside temperatures were lower with APF2 than APF1 although the emitter type was the same and the water application rates were similar. These temperature differences were attributable to the greater APF2 shadehouse surface area (SA) and volume (V) compared with APF1 and indicate that the SA and V of structures being heated need to be considered when designing water-based low-pressure fog heating systems. The ORM and both fog systems conserved water compared with using the conventional sprinkler irrigation systems. These results show the potential of water-based approaches for maintaining shadehouses above chilling temperatures during freeze events.

Chromosome Number and Karyotype Variation in Codiaeum variegatum Cultivars

Codiaeum variegatum (L.) Blume is one of the most popular ornamental foliage plants. It encompasses more than 300 recognized cultivars valued by their wide range of leaf shapes and vivid foliage colors. Thus far, only limited information is available regarding the genetic basis of their leaf morphological variation. This study investigated the chromosome numbers and karyotypes of seven phenotypically diverse cultivars. Root-tip cells were fixed, mounted, and observed under light microscopy. Results showed that chromosome numbers in the mitotic metaphase of the seven cultivars were high and variable and ranged from 2n = 66, 70, 72, 76, 80, 82, 84, to 2n = 96, indicating that the cultivars are polyploid and some could be aneuploid. Genetic mosaics occurred in one of the seven cultivars. Additionally, each cultivar had its own karyotype. There were no relationships between chromosome numbers or karyotypes and leaf morphology. Results from this study suggest that the morphological diversity among cultivars of this species could be in part attributed to high variation in chromosome numbers and karyotypes.

`Sterling' Dieffenbachia

Species and cultivars of Dieffenbachia Schott. (Araceae Juss.) have been important ornamental foliage plants for many decades. Their attractive foliar variegation, adaptability to interior environments, and ease of production are major reasons for their importance as ornamental foliage plants. Approximately 20 cultivars are commercially produced in Florida. Previously, most new cultivars were clones introduced from the wild or chance mutations of existing cultivars. Currently, cultivars are introduced into production from plant breeding programs (Henny 1995a, b; Henny and Chen, 2003; Henny et al., 1987). The hybrid Dieffenbachia `Sterling' was developed by the tropical foliage plant breeding program at the Mid-Florida Research and Education Center.

DNA Methylation Polymorphisms in Somaclonal-derived Cultivars of Ornamental Aroids

Plant tissue culture can induce a variety of genetic and epigenetic changes in regenerated plantlets, a phenomenon known as somaclonal variation. Such variation has been widely used in the ornamental foliage plant industry as a source for selection of new cultivars. In ornamental aroids alone, at least 63 somaclonal-derived cultivars have been released. In addition to morphological differences, many somaclonal aroid cultivars can be distinguished by amplified fragment length polymorphism (AFLP) analysis. However, a few cultivars have no detectable polymorphisms with their parents or close relatives by AFLP fingerprints. It is postulated that DNA methylation may be involved in the morphological changes of these cultivars. In this study, methylation-sensitive amplification polymorphism (MSAP) technique was used to study DNA methylation in selected somaclonal cultivars of Alocasia, Aglaonema, Anthurium, Dieffenbachia, Philodendron, and Syngonium. Results showed that polymorphisms were detected in the somaclonal cultivars, suggesting that DNA methylation polymorphisms may associate with tissue culture-induced mutation in ornamental aroids. This is the first study of methylation variation in somaclonal variants of ornamental foliage plants. The results clearly demonstrate that the MSAP technique is highly efficient in detecting DNA methylation events in somaclonal-derived cultivars.