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  • Author or Editor: Uttara C. Samarakoon x
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Clematis (Clematis ×hybrida) is among the flowering plants well-recognized by the retail consumer; however, production has not traditionally fit into standard greenhouse production systems. One reason is the relatively long 2-year production cycle from propagation to flowering. Four experiments were conducted with clematis ‘H.F. Young’ to understand the factors that influence shoot development and flowering of clematis so that strategies could be developed for bulking, providing a cold treatment, and flowering the plants with a shortened production time. The first experiment showed an increase in shoot and flower numbers and a decrease in time to flower as the duration of cold treatment increased from 0 to 9 weeks and the photoperiod increased from 9 to 16 hours. The second experiment resulted in greater shoot and flower numbers when plants were forced at 21 °C as compared with 27 °C. The third experiment showed that the application of ethephon (500 or 1000 mg·L−1) during bulking increased shoot formation (branching) as compared with the control or 500 mg·L−1 benzylaminopurine treatments. The fourth experiment showed that applications of 500 mg·L−1 ethephon along with a 16-hour photoperiod during the bulking period improved shoot number and flowering of the finished crop. The combined results provide guidelines for producing a well-branched, flowering clematis crop within 1 year from the start of propagation to the time of the first open flower.

Open Access

Vegetatively propagated unrooted cuttings typically are grown in equatorial locations and shipped via airfreight to propagators located in temperate climates. Cutting quality, defined as the resistance to external forces, such as physical damage and pathogen infection, impacts postharvest durability during shipping and propagation. During our previous studies, foliar application of calcium (Ca) in the form of Ca chloride was effective at increasing leaf mechanical strength of poinsettia (Euphorbia pulcherrima) and zonal geranium (Pelargonium ×hortorum). Calcium chloride applied at ≥800 mg·L−1 Ca caused phytotoxicity symptoms in poinsettia; therefore, in the current work, we investigated the use of chelated Ca by providing Ca at 40, 80, or 160 mg·L−1 and salicylic acid (SA) at 150 or 300 mg·L−1 to increase the mechanical strength of poinsettia leaves. Mechanical strength of leaves was assessed using a force-displacement graph generated from a texture analyzer using a ball probe to penetrate a unit area of a clamped leaf. The peak force to fracture the leaf and work-of-penetration, defined as the area under the force-displacement curve, were used as indicators of mechanical strength. Calcium concentration in the leaves increased by 27% with increased application of Ca from 0 to 160 mg·L−1. Peak force was 26% greater in treatments with Ca at 80 or 160 mg·L−1 compared with the untreated control. Work-of-penetration was 24% and 29% greater for treatments with Ca at 80 and 160 mg·L−1, respectively, compared with the control. Foliar application of SA did not affect leaf mechanical strength. Chelated Ca applied at 160 mg·L−1 Ca caused visual phytotoxicity symptoms; thus, applications of 80 mg·L−1 Ca are recommended to improve resistance to physical damage for poinsettia leaves.

Open Access

Clematis (Clematis ×hybrida) has not traditionally fit into the standard production system for vegetatively propagated herbaceous perennials because of the lack of commercially available unrooted cuttings and relatively poor rooting success. We investigated strategies to improve stock plant production and propagation of clematis. The first experiment compared the propagation performance of four cultivars (H.F. Young, Reiman, Little Duckling, and Pinky). The second experiment examined cutting productivity and propagation performance of clematis cultivars when stock plants were grown at 21 or 27 °C and propagated with or without the application of rooting hormone. Stock plants grown at 27 °C resulted in greater cutting numbers and greater dry weights in the rooted cuttings after propagation. The third experiment demonstrated the effects of the origin of the cuttings of the stock plant on cutting productivity and propagation performance. When shoots emerged from underground buds, as compared with axillary buds, the numbers of cuttings and fresh and dry weights of the rooted cuttings were increased by nearly 50%. The promotion of shoot emergence from underground buds on the stock plants led to continuous cutting production for five cycles, with cutting number increasing from 67 to 128 cuttings/plant. Year-round cutting supplies can be achieved by trimming stock plants to the substrate surface to promote juvenile shoot development while maintaining stock plants under long-day photoperiods and warm temperatures (27 °C).

Open Access

During the production of ornamentals in commercial greenhouses, hanging baskets are often grown above the bench or floor space to maximize production. These hanging baskets impact the light environment delivered to the crop underneath. An experiment was conducted to quantify the effect of hanging basket density (determined by number of lines of containers per greenhouse bay and container spacing per line), container content (with plants vs. no plants), and container color (white vs. green) on photosynthetic photon flux (PPF) transmission and red (R) and far-red (FR) light measurements at the greenhouse floor under the hanging basket treatments. Interception of PPF was calculated as a proportion of the treatment with no hanging baskets. Interception of PPF increased as hanging basket density increased, from 5.3% interception at 0.21 containers/yard2 to 25.5% interception at 2.57 containers/yard2. Green containers intercepted 36.1% more radiation than the white containers. Presence of plants in the containers resulted in 62.3% greater PPF interception than containers without plants. R:FR was reduced from 1.15 measured under hanging basket treatments without plants to 1.07 under hanging basket treatments containing plants.

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Poinsettia stock plants consist of a dense canopy of competing shoots, and the growth and development of these individual shoots have not been previously quantified. The effects of air temperature, daily light integral (DLI), and canopy density (CD) were investigated on poinsettia (Euphorbia pulcherrima Willd. ex. Klotsch) ‘Freedom Red’ shoot development in a stock plant canopy. Plants were grown at two constant temperatures (20.3 or 25.7 °C), five CD (43, 86, 129, 172, or 215 shoots/m2), and three DLI treatments (2.6, 4.4, or 7.7 mol·m−2.d−1 for the September planting and 4.0, 6.0, or 10.6 mol·m−2.d−1 for the January planting). Shoot position at the final data collection was used to assign shoots to different levels within the canopy; Level 1 = the four highest shoots, Level 2 = the next four highest shoots, and so forth for Levels 3, 4, and 5. Temperature did not significantly affect leaf unfolding rate (LUR), shoot fresh mass (FM), or shoot caliper, whereas DLI and CD affected shoot growth and development. LUR and FM increased as DLI increased from 2.6 to 10.6 mol·m−2.d−1, whereas LUR and FM decreased on the uppermost shoots in the canopy, e.g., Level 1 shoots, as CD increased from 43 to 129 shoots/m2. Therefore, higher CD required higher DLI to achieve similar LUR and FM. Shoot caliper on Level 1 shoots increased from 6.3 to 7.4 mm as CD decreased from 129 to 43 shoots/m2; and shoot caliper increased from 5.8 to 7.6 mm as DLI increased from 4.0 to 10.6 mol·m−2.d−1. The DLI environment needs to be managed to accommodate greater CD, to sustain growth and development of individual shoots within the canopy of poinsettia stock plants.

Free access

Vegetatively propagated unrooted cuttings are typically imported to the United States from Central America. Death or damage of cuttings during shipping and propagation can be reduced if cuttings can be made more resistant to external forces, such as physical damage or pathogen infection. However, strategies to develop durable cuttings via treating stock plants have not been previously quantified in controlled studies. During the current study, mechanical strength of leaves and resistance to infection by Botrytis cinerea were evaluated after weekly applications of calcium chloride (CaCl2) as a foliar spray to stock plants that delivered calcium (Ca) at the concentrations of 0, 400, or 800 mg·L−1. A texture analyzer quantified the peak force required to fracture the leaf and the work of penetration,or area under the force–displacement curve, and these measurements were indicators of mechanical strength. For poinsettia (Euphorbia pulcherrima Willd. ex Klotzsch) cuttings at the time of harvest from the stock plant, work of penetration increased by 10% with the application of 800 mg·L−1 Ca compared with the control, whereas peak force by 9%. For zonal geranium (Pelargonium ×hortorum Bailey), work of penetration increased 15% with the application of 800 mg·L−1 Ca compared with the control. Calcium concentration in the leaves increased from 1.2% to 2.0% in geranium and from 1.0% to 1.6% in poinsettia with increasing application from 0 to 800 mg·L−1 Ca. In poinsettia, disease incidence in response to inoculation with B. cinerea spores was 55% and 15% less with CaCl2 applications compared with controls with water and surfactant, respectively, whereas CaCl2 application to geranium did not affect disease incidence.

Free access

Cut flower productivity and quality of gentian is associated with growth and development of crown buds. Experiments were carried out with the gentian cultivar Showtime Diva to identify the response to treatments that break dormancy [cold temperature (chilling), gibberellic acid (GA3)] applied at different stages of development of crown buds (plants with nonemerged crown buds, shoots recently emerged, or shoots emerged and elongated). The comparative growth potential of crown buds within the cluster was also investigated. At the stages of development examined, the application of GA3 (100 ppm) increased emergence of crown buds as shoots, leading to development of more flowering shoots. A similar response was observed with exposure to cold, but only on plants with nonemerged crown buds. Shoot emergence increased in response to increased duration of cold from 0 to 42 days (5 °C). Both chilling and GA3 could potentially be used to reduce the duration to, and spread of, harvest maturity if applied before shoot emergence. The hierarchical relationship of buds in crown bud clusters led to differential responses to application of GA3. Buds ontogenetically positioned at the proximal end of the bud cluster took a similar duration to reach shoot emergence or harvest maturity. For buds located at the distal end there was a positive correlation between ontogenetic bud position and the duration to reach shoot maturity. Shoot length and number of nodes at harvest maturity showed slight negative correlations with the position of the bud in the bud cluster. The results provide an explanation for possible sources of the variation in quality and quantity of floral shoots, and spread in time to harvest maturity within a single plant, and with development stage.

Free access

Botrytis blight on petunia flowers causes significant losses in the postharvest environment. Infection occurs during greenhouse production, and symptoms are expressed during transport. This phenomenon is termed petunia flower meltdown because of the rapid collapse of flower petal tissue as the plants are transported from the production greenhouse to the retail store. The objective of this study was to determine the effect of calcium (Ca) spray applications on botrytis blight severity in petunia flowers. For the first experiment, petunia ‘Pretty Grand Red’ plants were sprayed twice per week for 2 weeks with calcium chloride (CaCl2) at rates of 0, 400, 800, and 1200 mg·L−1 Ca. A fungicide (cyprodinil, 37.5%; fludioxonil, 25%) was used as an additional control treatment. Twenty-four hours after the last treatment, freshly opened flowers were harvested, placed into a humidity chamber with 99% relative humidity, and inoculated with a Botrytis cinerea spore suspension (1 × 104 conidia/mL). Disease progression was recorded every 12 hours for 72 hours. The results showed a 96% reduction in botrytis blight severity as Ca concentration increased from 0 to 1200 mg·L−1 Ca. The Ca treatments provided better disease control than the fungicide treatment because of the fungicide resistance of the isolate used in the study. A second experiment was performed to determine whether the beneficial response to CaCl2 application was influenced by chlorine (Cl) or the electrical conductivity (EC) of the spray solutions, and no significant responses were observed. These studies prove Ca is the sole source of the reduction in botrytis blight severity following treatment with CaCl2 sprays, and demonstrate the benefit of using Ca as a tool for the management of botrytis blight on petunia flowers.

Open Access

The time to harvest maturity of flowering shoots and the extent and source of variability in maturity dates differed among cultivars of gentian (Gentiana sp.), with a wider spread in time to harvest maturity in Showtime Starlet (41 days) than Showtime Diva (35 days) and Showtime Spotlight (29 days). Cultivars also differed by more than twice in their plant-to-plant variability in time to harvest. Although later-emerging shoots reached harvest maturity more quickly than earlier-emerging shoots, the use of growing degree-days (GDD) for this field-grown cut flower did not account for differences. For ‘Showtime Diva’, 77% of outliers reached harvest maturity at the beginning of the season (i.e., before the 10th percentile). For ‘Showtime Spotlight’, only 20% of shoots classified as outliers flowered early with the remaining 80% emerging late (i.e., after the 90th percentile). Strategies to control the spread in time to harvest maturity in late-maturing cultivars such as Showtime Starlet should focus on uniform shoot emergence and controlling temperature during growth. Although strategies to achieve uniform shoot emergence should also be targeted for ‘Showtime Diva’, controlling temperature during the growing season would not appear to offer significant control of the spread in time of harvesting floral shoots. However, in earlier-maturing cultivars such as Showtime Spotlight, strategies will primarily require a greater understanding of the factors influencing the variability in maturation of shoots within individual plants before, and after, emergence.

Full access

Shoot productivity and overwintering survival of gentians (Gentiana sp.) are determined by the initiation and subsequent development of crown bud clusters. Understanding of the anatomical features and origins of crown buds and bud clusters, and plant ontogeny, the morphological features of crown buds, and their associated development is required to achieve manipulation of bud initiation, emergence, and development. Anatomical features of the crown bud clusters were examined using both light and confocal microscopy using hybrids of Gentiana triflora × G. scabra. The initiation of bud clusters presented characteristics typical of adventitious buds in terms of their origin and presence of external vascular connection to the parental tissue. In contrast, crown buds forming subsequently within the cluster developed as axillary buds within that initial bud, collectively forming on a compact stem with minimal internode elongation. Stem elongation within the cluster after application of gibberellic acid enabled identification of a hierarchical arrangement of buds within the cluster with one bud at each node and arranged spirally at 90°. Arrangements of buds within the cluster were different from the opposite decussate phyllotaxis in floral shoots with two axillary buds at each node. Based on the current study, a crown bud cluster originated from a first bud initial, which was adventitious followed by development of subsequent crown buds within the cluster as axillary buds from this first bud initially with a single bud developing at each node.

Free access