Sweet Viburnum Research Articles

Identification and fungicide screening of Phyllosticta capitalensis causing leaf spot on sweet viburnum in China

Sweet viburnum (Viburnum odoratissimum Ker-Gawl.) is a widely used ornamental plant, which has dense branches and leaves, and fast spreading and evergreen habit. In October 2022, leaf spot symptoms were observed in a hedge of sweet viburnum in Yuanshi Garden, Ningbo, China. Fungi were isolated from symptomatic leaves, and were identified using morphological characteristics and phylogenetic analyses of partial sequences of internal transcribed spacer (ITS), actin (act), and translation elongation factor 1-alpha (tef1-α), and were evaluated in pathogenicity tests. The causal agent of sweet viburnum leaf spot was identified to be Phyllosticta capitalensis. Effects of seven fungicides on P. capitalensis were assessed in vitro. Fungicide EC50s (mg L-1) against P. capitalensis were: 270.77 for 75% chlorothalonil (WP); 0.02 for 250 g L-1 azoxystrobin SC; 0.27 for 10% difenconazole WDG; 0.02 for 75% trifloxystrobin + tebuconazole WDG, 9.03 for 35% fluopyram + tebuconazole SC, 5.90 for 500 g L-1 fluazinam SC, and 89.11 for 10% prothioconazole SC. Among these, azoxystrobin SC and trifloxystrobin + tebuconazole WDG could be used for control of viburnum leaf spot. This is the first report of P. capitalensis causing leaf spot of sweet viburnum, and this study provides guidance for chemical management sweet viburnum leaf spot, and on other host plants.

First Report of Leaf Spot Caused by Corynespora cassiicola on Viburnum odoratissimum var. awabuki (Sweet Viburnum) in China.

Sweet viburnum [Viburnum odoratissimum Ker-Gawl. var. awabuki (K. Koch) Zabel ex Rumpl.] belonging to the family Adoxaceae, is a medical and landscape plant, native to Korea (Jeju Island), Taiwan, and Japan (Edita 1988). In June and September 2019, leaf spots were observed on approximately 65% to 80% of sweet viburnum plants in a hedgerow located in Fenghe Xincheng District (28°41'52.9"N 115°52'14.3"E) in Nanchang, China. Initial symptoms of disease appeared as dark brown spots surrounded by red halos (Figure 1 A), which expanded irregularly. Finally, the center of the lesions desiccated and became light-brown, surrounded by a deep-red halos (Figure 1 B). Ten leaf samples with typical symptoms were collected and washed with tap water for about 15 min. The tissue between the healthy and necrotic area (ca. 4 mm × 4 mm) was cut with a sterile scalpel and surface sterilized with 70% alcohol for 45 s, 2% NaClO for 2 min, washed in sterile deionized water three times, dried on sterilized filter paper, then placed in Petri dishes and incubated at 25℃ in the dark. After 3 to 5 days, the hyphal tips from the edges of growing colonies were transferred to fresh PDA dishes. Eventually, 54 fungal isolates were obtained and, of these, 39 isolates were identical in their morphological characteristics. Morphological analysis was performed according with Ellis (1971). The isolate S18, chosen as representative, formed a gray to grayish brown colony with concentric circleson PDA, and a diameter of 8.5 to 9 cm after 7 days incubation at 25℃ (Figure 1 G). Conidia were hyaline, straight or slightly curved, needle shaped, truncate at the base, and acuminate at the tip, with 2 to 6 pseudosepta, 18.90 to 38.38 µm (avg. = 27.51 µm) × 1.64 to 4.50 µm (avg. = 2.60 µm) (n = 36) (Figure 1 H). The genes of fungal isolates (i.e., ITS, tub2 and ACT) were amplified with ITS4/ITS5 for ITS (White, Bruns et al. 1990), Bt2a/Bt2b for tub2 (Glass and Donaldson 1995) and ACT783R/ACT512F for ACT (Carbone and Kohn 1999) and sequenced. The sequences were deposited in GenBank (MW165772 for ITS, MW175900 for ACT and MW168659 for tub2), which showing greater than 99.1% similarity to multiple C. cassiicola accessions, respectively. Pathogenicity tests were performed on healthy leaves in field by inoculating surface-sterilized mature leaves with puncture wound (Figure C) and non-wounded young leaves with 20 µL of a conidial suspension (105 conidia ml-1) (Figure F and G) at 26℃. After 4 to 7 days, all inoculated leaves reproduced similar symptoms as observed initially in the field (Figure 1 C, E and F). To fulfill Koch's postulates, the fungus was isolated on PDA from the margins of leaf spots on inoculated leaves and confirmed as C. cassiicola by morphological characters and ITS gene sequencing. Previously, C. cassiicola was reported as an endophyte on Viburnum spp. and Viburnum odoratissimum (Alfieri et al. 1994). More recently, C. cassiicola has been reported as a pathogen of many plant species in China, such as kiwifruit (Cui, Gong et al. 2015), American sweetgum (Mao, Zheng et al. 2021), castor bean (Tang, Liu et al. 2020), and holly mangrove (Xie, He et al. 2020). To our knowledge, this is the first report of leaf spot disease on sweet viburnum caused by C. cassiicola in China and the precise identification of the causal agent will be useful for its management.

Use of Routine Leaching Fraction Testing to Guide Irrigation at a Container Nursery

Abstract Efficient irrigation during container plant production is difficult to achieve as irrigation is scheduled daily or multiple times per day to maintain an adequate supply of water in the limited substrate volume. Leaching fraction (container drainage/water applied) testing is one strategy to monitor and adjust irrigation to limit excessive container drainage. We compared an automated irrigation schedule based on routine leaching fraction testing and weather (LFI) with a nursery's traditional irrigation practice (TIP). Compared to TIP, LFI reduced water applied in four of five sprinkler-irrigated trials without a notable growth affect; LFI increased water applied in a fifth trial but plant growth was also increased. Compared to TIP, LFI reduced water applied in all three micro-irrigated trials but also reduced growth in one of the trials. LFI reduced water applied by an average of 21% [57.8 vs. 73.1 kL·ha−1· d−1 (15,300 gal/acre/day) or $3,000 ha−1yr−1 ($1,200/acre/year) at a pumping cost of $0.53/kL ($0.20/1000 gal). We concluded that the greater economic benefit of water savings was to provide increased capacity for additional production under consumptive water use limitations rather than to reduce the unit cost of production. Index words: automation, evapotranspiration, sprinkler, micro-irrigation, weather. Species used in this study: Leyland cypress, Cupressus × leylandii A.B. Jacks. and Dallim., Parson juniper, Juniperus squamata Gordon ‘Expansa Parsonii', crape myrtle, Lagerstroemia indica L. × fauriei Koehne ‘Natchez', Indian hawthorn, Raphiolepis indica (L.) Lindl., sweet viburnum, Viburnum odoratissimum Ker Gawl.

Water use and drainage of subtropical, mixed landscapes varies with turf coverage and season

We conducted a three-year drainage lysimeter study of mixed (woody plant-turf) landscape water demand relative to reference evapotranspiration, drainage, and plant growth in humid, subtropical central Florida. The aim was to develop information to guide more efficient water planning, landscape design, and irrigation management in a seasonally dry monsoon climate using three representative landscape species – southern magnolia (Magnolia virginiana), sweet viburnum (Viburnum odoratissimum), and St. Augustinegrass (Stenotaphrum secundatum) – at turf coverage of 90, 75, and 60% of the total landscape area. Water inputs (daily rainfall, irrigation) and drainage were recorded with a datalogger to calculate monthly actual evapotranspiration (ETA) for each lysimeter using a water balance approach. Growth was measured non-destructively (magnolia height, canopy and trunk diameter, viburnum dry mater, canopy cross section, and volume) every three weeks, while turf clippings were collected during the spring to late fall growing season. Woody plants imbedded in turf with ostensibly deeper root systems underlying turfgrass roots were more efficient at scavenging water, minimizing drainage, and leaching risk. Reducing turfgrass coverage to 60% diminished drainage by 70 cm in the wet season and 50 cm in the dry season compared to 90% turfgrass cover, and increased rainfall utilization rate to 0.81 compared to 0.40 for 90% turf across both seasons. Mixed turf-woody plant landscape ETA differed minimally across turf coverage treatments during the dry season, with approximately 70% of reference ETA versus 90% during the wet season, likely due to less surface evaporation. To conserve water and reduce drainage during the monsoonal dry season, mixed turf-woody plant landscape irrigation can be scheduled based on water demand at 70% of local evapotranspiration (0.7 Plant Factor). These results give water suppliers and landscape architects tools to design urban landscapes and develop regulations to efficiently promote and track mixed landscape irrigation water consumption in a monsoonal climate with a pronounced dry season. Further, water managers can reduce drainage and risk of groundwater pollution by encouraging design of landscapes with woody plants imbedded in turfgrass to scavenge water moving below the turfgrass root zone.

First Report of Alternaria spp. Causing Leaf Spot on Sweet Viburnum in China.

Sweet viburnum [Viburnum odoratissimum (L.) Ker Gawl] is an evergreen shrub mainly cultivated along roadsides in urban landscapes and also in parks and residential areas. A foliar disease occurred on about 40% of sweet viburnum plants near Anhui Grand Theatre, Anhui Province of China in June 2019. In early stages of sweet viburnum infection, the symptoms appeared as small brown spots ranged in length from 2 to 3 millimeters on the leaves. The spots developed on the upper, middle, and lower leaves of the plant, however, the upper leaves got more severely affected. As the disease develops, the spots enlarged and became rectangular or oval, brown to dark-brown, and their centers became ashen gray. In later stages of infection, the diseased leaves became wilting. Diseased leaves were surface disinfested and three small sections (2-3 mm2) were cut from the margin of the lesions. Sections were placed in 1.5% NaClO for 2 min, submerged in three changes of sterilized distilled water for 1 min each, placed onto potato dextrose agar (PDA) medium amended with 50 μg/ml of ampicillin and kanamycin, and incubated at 25℃ for 3 days. The mycelium from the leading edge of colonies growing from the tissue was sub-cultured onto a PDA plate for 3 days, followed by spore induction (Simmons 2007) and single spore isolation to obtain a pure culture of the putative pathogen. Colonies of one single spore isolate HF0719 were rounded, grayish white with dense aerial mycelium viewed from above and dark brown viewed from below. On potato carrot agar (PCA) medium, conidiophores were branched or occasionally unbranched. On branched conidiophores, conidia were in dwarf tree-like branched chains of 2-5 conidia. On unbranched conidiophores, conidia were simple or in chains of 2-8 conidia. Conidia were light brown or dark brown, ovoid, ellipsoidal to fusiform, and ranged in size from 7 to 26.5 × 4.5 to 11 μm with an average size of 16 × 7 µm based on 500 spore observations, with one beak and 1-7 transverse, 0-3 longitudinal, and 0-3 oblique septa. Beaks were ranged in (1.5-)2-10(-16) μm long. Based on cultural and morphological characteristics, isolate HF0719 was identified as Alternaria spp. (Simmons 2007). For molecular identification, total genomic DNA was isolated from mycelia collected from 7 day-old colonies of isolate HF0719 using the fungal genomic DNA extraction kit (Solarbio, Beijing, China). Fragments of five genes, including those encoding glyceraldehyde-3-phosphate dehydrogenase (gpd), plasma membrane ATPase, actin, calmodulin, and the Alternaria major allergen (Alt a1) regions of isolate HF0719 were amplified and sequenced using primer pairs gpd1/gpd2 (Berbee et al. 1999), ATPDF1/ATPDR1, ACTDF1/ACTDR1, CALDF1/CALDR1 (Lawrence et al. 2013), and Alt-for/Alt-rev (Hong et al. 2005), respectively. The obtained nucleotide sequences were deposited into GenBank as accession numbers: gpd, MT614365; ATPase, MT614364; actin, MT614363; calmodulin, MN706159; and Alt a1, MN304720. Phylogenetic tree using a maximum likelihood bootstrapping method based on the five-gene combined dataset in the following order: gpd, ATPase, actin, calmodulin, Alt a1 of HF0719 and standard strains representing 120 Alternaria species (Lawrence et al. 2013) was constructed. Isolate HF0719 formed a separate branch. On the basis of morphological characteristics and phylogenetic pattern, isolate HF0719 was identified as Alternaria spp.. A pathogenicity test was performed by rubbing 32 healthy leaves of six 5-year-old sweet viburnum plants with a cotton swab dipped in spore suspension containing 2.6 × 106 spores/ml, following leaf surface disinfection with 70% ethanol in the open field. Sterilized distilled water was used as control. The average air temperature was about 28℃ during the period of pathogenicity test. Eleven days after inoculation, 100% of inoculated leaves showed the leaf spot symptom identical to symptoms observed in the field. Control leaves were symptomless. The experiment was done three times. The re-isolated pathogen from the leaf lesion had the same morphological and molecular characteristics as isolate HF0719, thus satisfying Koch's postulates. The genus Alternaria has been reported to cause leaf spot on sweet viburnum in Florida, USA (Alfieri et al. 1984). To our knowledge, this is the first report of Alternaria spp. causing leaf spot on sweet viburnum in China, a highly valued ornamental plant. Our findings will contribute to monitoring and adopting strategies for manage leaf spot disease on sweet viburnum.

Nitrogen Fertilizer Rate, Timing, and Application Method Affects Growth of Sweet Viburnum and Nitrogen Leaching from Simulated Planting Beds

Several Florida cities and counties ban fertilization during the summer rainy season (fertilizer blackout). Little research is available to support or contradict the underlying justifications for these policies. We used large-volume lysimeters to address the impacts of several fertilization regimes on plant growth and aesthetics of sweet viburnum (Viburnum odoratissimum Ker Gawl.) and nitrogen (N) leaching from landscape beds during shrub establishment and maintenance. Three levels of N fertilization (98, 195, and 293 kg·ha−1), two levels of application method (per plant and broadcast), two levels of fertilization timing (regular and blackout), and an unfertilized control (0 kg·ha−1 N) were applied to lysimeters in a completely randomized design with three replicates (3 × 2 × 2 factorial plus untreated control). Increasing fertilization rate increased plant growth and improved plant quality, but also increased N leaching from lysimeters. Including a summer fertilization blackout period reduced nitrate + nitrite (NO3 + NO2-N) loading from lysimeters during sweet viburnum establishment [0 to 28 weeks after planting (WAP)] compared with year-round fertilization at the same total N rate without adversely impacting plant growth or aesthetics. However, NO3 + NO2-N loads from lysimeters were higher when fertilizers were applied on the summer blackout application schedule during the shrub maintenance period. Targeted (per plant) fertilization beneath the dripline of sweet viburnum at an annual N rate of 195 kg·ha−1 can maintain plant health while limiting N leaching losses on a year-round or blackout fertilization schedule.

CIRRIG: Weather-based Irrigation Management Program for Container Nurseries

A goal of irrigation best management practices in container nurseries is to conserve water while maintaining optimal plant growth and quality. A web-based, container irrigation management program (CIRRIG) was developed to automatically provide daily irrigation run times for sprinkler-irrigated crops in container nurseries. The program estimates evapotranspiration rates based on weather uploaded from a weather station located on-site and plant production conditions monitored in each zone and adjusts irrigation run times based on irrigation application rate, the plant’s irrigation-capturing ability (for sprinkler irrigation), desired leaching fraction, and irrigation system uniformity. For this project we interfaced CIRRIG output with a programmable logic controller (PLC) to automatically irrigate a sprinkler-irrigated crop at a container nursery in Florida. Sweet viburnum (Viburnum odoratissimum) in 10-inch-diameter containers were grown by the nursery for 24 weeks in adjacent irrigation zones, one controlled automatically using CIRRIG and the other by the nursery’s traditional practice of manually turning on and off irrigation. Water use was monitored with flowmeters and plant growth by measuring plant size and shoot dry weight periodically throughout the trial. Plant growth was not different (P < 0.05) because of irrigation practice. CIRRIG reduced water use during the study period by 21% (42 vs. 53 inches) compared with the nursery’s irrigation practice. An assessment of the water-saving benefits of making daily adjustments to irrigation run times based on weather including rain indicated savings of 25% and 40% compared with biweekly adjustments with and without automatic rain cutoff, respectively. This trial demonstrated that CIRRIG coupled with an on-site weather station and a computer-controlled irrigation system can be used to manage irrigation while conserving water in a container nursery.

Growth and Quality Response of Woody Shrubs to Nitrogen Fertilization Rates during Landscape Establishment in Florida

Despite inconsistent reports of nitrogen (N) fertilization response on growth of landscape-grown woody ornamentals, broad N fertilization recommendations exist in the literature. The objective of this research was to evaluate the growth and quality response of three landscape-grown woody shrub species to N fertilizer. Three ornamental shrub species, ‘Alba’ indian hawthorn (Raphiolepis indica), sweet viburnum (Viburnum odoratissimum), and ‘RADrazz’ (Knock Out™) rose (Rosa) were transplanted into field soils in central Florida (U.S. Department of Agriculture hardiness zone 9a). Controlled-release N fertilizer was applied at an annual N rate of 0, 2, 4, 6, and 12 lb/1000 ft2 for 100 weeks. Plant size index measurements, SPAD readings (a measure of greenness), and visual quality ratings were completed every month through 52 weeks after planting (WAP) and then every 3 months through 100 WAP. Plant tissue total Kjeldahl N (TKN) concentrations and shoot biomass were measured at 100 WAP. Results of regression analysis indicated little to no plant response (size index, biomass, SPAD) to N fertilizer rate. Shrub quality was acceptable for all species through 76 WAP regardless of the N fertilization rate. However, quality of rose and sweet viburnum fertilized with N at the low rates (<2 lb/1000 ft2) was less than acceptable (<3 out of 5) after 76 WAP. Results suggest that posttransplant applications of fertilizer may not increase plant growth, but that low-to-moderate levels of N fertilization (2 to 4 lb/1000 ft2 per year) may help plant maintain quality postestablishment.

Evapotranspiration-based Irrigation Scheduling for Container-grown Viburnum odoratissimum (L.) Ker Gawl.

The capacity for evapotranspiration (ET)-based irrigation scheduling to reduce runoff volume and nutrient leaching was tested in Fall 2004 and Spring 2005. Runoff (container leachate plus unintercepted irrigation and precipitation) was collected continuously for 17 weeks during production of sweet viburnum [Viburnum odoratissimum (L.) Ker Gawl.] in 2.4-L (16-cm top diameter) containers fertilized with an 18N–2.6P–10K polymer-coated, controlled-release fertilizer. Treatments were a factorial arrangement of two irrigation rates (fixed rate of 1 cm·d−1 or a variable, ET-based rate) and two fertilizer rates (15 or 30 g/container in 2004 and 10 or 15 g/container in 2005). Averaged over the two experiments and compared with the 1-cm·d−1 rate, ET-based irrigation reduced the amount of irrigation water applied (L/container) by 39% and runoff volume (L/container) by 42% with greatest reductions observed during the second half of the 2004 experiment and the first half of the 2005 experiment. Compared with 1-cm·d−1 rate, ET-based irrigation reduced runoff nitrogen (N), phosphorus (P), and potassium (K) (mg/container) by 16%, 25%, and 22%, respectively, in 2004 and runoff K 15% in 2005 with irrigation effects varying on a weekly basis. Irrigation treatments did not affect the response of plants to fertilizer rate. Because shoot dry weight was unaffected by irrigation treatments, results indicate that compared with a fixed irrigation rate, ET-based irrigation can reduce irrigation and runoff volumes and to a lesser extent nutrient loss while providing adequate water for plant growth.

Posttransplant Irrigation Frequency Affects Growth of Container-grown Sweet Viburnum in Three Hardiness Zones

The survival and quality of shrubs planted in the landscape from containers is dependent on irrigation to ensure the development of a healthy root system. This study determined the effect of irrigation frequency on survival, quality, canopy growth index, root to canopy spread ratio, and dry root and shoot biomass of Viburnum odoratissimum Ker-Gawl. (sweet viburnum) planted in Florida in USDA hardiness Zones 8b (Citra, FL), 9a (Balm, FL), and 10b (Ft. Lauderdale, FL). Sweet viburnum shrubs were planted into the landscape from 11.4-L (#3) containers and irrigated with 3 L every 2, 4, or 8 days. Shrubs were planted on eight dates over a 2-year period (2004 to 2006). Irrigation frequency during the 12- to 22-week irrigation period had no significant effect on sweet viburnum survival or aesthetic quality at any location. In addition, there was no irrigation effect on root spread, root to shoot biomass ratio, or root biomass for shrubs planted in Zones 8b or 9a. However, sweet viburnum irrigated every 2 days had greater canopy growth index at 28 and 104 weeks after planting than shrubs irrigated every 4 or 8 days in Zone 8b and every 8 days in Zone 9a. When planted in Zone 10b, sweet viburnum irrigated every 2 days exhibited greater growth index, shoot biomass, and root biomass than plant receiving irrigation every 4 days. Although more frequent irrigation (every 2 days) resulted in more plant growth in Zones 8b and 10b, sweet viburnum survived and grew after planting under natural rainfall conditions provided they were irrigated with 3 L of water every 8 days during establishment until roots reached the canopy edge in hardiness Zones 8b and 9a and every 4 days in hardiness Zone 10b. Subsequent supplemental irrigation (hand-watering) was only needed after irrigation was ended when plants exhibited visible signs of drought stress and there was no measurable rainfall for 30 consecutive days.

Consequences of Excessive Overhead Irrigation on Runoff during Container Production of Sweet Viburnum

Abstract The effects of irrigation rate on volume and nutrient content of runoff were investigated. Runoff (leachate plus un-intercepted irrigation and rain) was collected weekly for 20 weeks during production of trade #1 (2.7-liter) sweet viburnum [Viburnum odoratissimum (L.) Ker-Gawl.] fertilized with a resin-coated, controlled-release fertilizer [Osmocote 18N–2.6P–10K (18–6–12), 8–9 month 21C (70F)]. Treatments were a factorial arrangement of two irrigation rates [1 (IRR1) or 2 (IRR2) cm/day (0.39 or 0.79 in)] and two fertilizer rates [15 (FRT15) or 30 (FRT30) g/container (0.53 or 1.06 oz)]. Total runoff volume was 970 liters/m2 (2380 gal/100 ft2) for IRR1 and 2220 liters/m2 (5450 gal/100 ft2) for IRR2 which was 49 and 69%, respectively, of total irrigation plus rainfall. Increasing the irrigation rate from 1 to 2 cm/day increased leaching losses of N, P, and K 34, 38, and 45%, respectively, with FRT15 and 21, 28, and 23%, respectively, with FRT30. Increasing the irrigation rate increased nutrient loads (g/m2) but decreased nutrient concentrations (mg/liter) in runoff.

Effects of Container Spacing Practice and Fertilizer Placement on Runoff from Overhead-Irrigated Sweet Viburnum

Abstract Information on how management practices affect runoff volume and nutrient content is needed to improve irrigation and fertilizer efficiency while minimizing environmental impacts. Runoff (leachate plus unintercepted irrigation and rain) was collected weekly for 20 weeks during production of sweet viburnum (Viburnum odoratissimum (L.) Ker-Gawl.) in trade #1 (2.7 liter) containers fertilized with 15 g (0.53 oz) of a resin-coated, controlled-release fertilizer Osmocote 18N–2.6P–10K (18–6–12), 8–9 month 21C (70F)] and overhead-irrigated with water at 1 cm/day (0.39 in). Treatments were a factorial arrangement of two container spacing practices [spaced at planting (SP) or spaced midseason (SM)] and two fertilizer placement methods [incorporated (INC) or surface-applied (SURF)]. Cumulative runoff volume averaged 1590 liters/m2 (3900 gal/100 ft2) or 66% of irrigation plus rain and was 9% higher for SP than SM. A 37% reduction in shoot dry weight of SP versus SM plants was attributed to heat stress in SP containers. SURF decreased N, P, and K leaching losses (mg/container) 42, 42, and 25%, respectively, at SP and 16, 25, and 4%, respectively, at SM. Nutrient leaching losses as a percent of applied were 11–18% for N, 7–13% for P, and 19–28% for K. Total nutrient loads in runoff were 4.6–11.1 g/m2 for N, 0.48–1.25 g/m2 for P, and 5.8–10.1 g/m2 for K with peak nutrient loss occurring during the first two weeks after planting.

Irrigation Affects Landscape Establishment of Burford Holly, Pittosporum, and Sweet Viburnum

Ilex cornuta Lindl. & Paxt. ‘Burfordii Nana’ (dwarf burford holly), Pittosporum tobira [Dryand]. ‘Variegata’ (pittosporum), and Viburnum odorotissimum Ker Gawl. (sweet viburnum) were transplanted into field plots in an open-sided, clear polyethylene-covered shelter to evaluate growth, aesthetic quality, and establishment rates in response to 2-, 4-, or 7-d irrigation frequencies. Establishment was delayed 1 to 2 months for I. cornuta ‘Burrford Nana’ irrigated every 7 d compared with 2- and 4-d frequencies; however, growth and aesthetic quality were similar among treatments. Plants irrigated every 7 d also had higher cumulative water stress levels. Leaf area, shoot dry weight, and total biomass increased among P. tobira ‘Variegata’ and V. odorotissimum irrigated every 2 d. Pittosporum tobira ‘Variegata’ and V. odorotissimum irrigated every 2 d also had greater canopy size and root dry weight, respectively. Neither cumulative water stress nor establishment was affected by irrigation frequency for either species.

Nitrogen Uptake and Allocation in Sweet Viburnum During a Root Growth Flush

ABSTRACT Most woody ornamentals exhibit episodic growth flushes and nitrogen (N) uptake has also been demonstrated to be seasonal. However, there is little information on N uptake in relationship to plant growth cycle. In this study, N uptake and allocation of sweet viburnum during periods of low and high root elongation rates were studied. Plants were fertilized with ammonium nitrate (15NH4 15NO3) and after 6 d N absorption was determined. Significantly more N was absorbed by plants with low root elongation rate compared with plants with high root elongation rate. About 70% of the N absorbed by plants with low root elongation rate was allocated to the mature leaves compared to 35% on plants with high root elongation rate. It was evident that root growth activity influenced N absorption and allocation. Although only a small amount of the N absorbed by plants with low root elongation rates was allocated to the immature leaves, significantly more N was allocated to the immature leaves by plants with high root elongation rates. It is possible that the N necessary to support immature leaf growth, when root elongation rate is low, is provided by mobilization from other parts, possibly mature leaves.

Influence of nitrogen application rate on the magnitude of root and shoot growth flushes of Viburnum odoratissimum Ker-Gawl

Most trees and shrubs have cyclic, rather than continuous shoot and root growth. Growth cycles have important implications with regards to transplant and fertilization timing. Although growth cycles of several woody species have been characterized, no information is available on sweet viburnum (Viburnum odoratissimum). A series of experiments was conducted to study shoot and root growth flushes of sweet viburnum and the influence of nitrogen fertilization on flushes. Plants were grown in observation tubes and kept under greenhouse conditions. Sweet viburnum exhibited alternating periods of root and shoot elongation, and the root elongation peak preceded shoot elongation peak by 6–18 days. Increased nitrogen fertilization rate negatively impacted the magnitude and number of root growth flushes. Further research is needed to determine when maximum nitrogen uptake is occurring, relative to root and shoot growth cycles.

Micropropagation of sweet viburnum (Viburnum odoratissimum)

A micropropagation protocol for shoot culture of sweet viburnum (Viburnum odoratissimum) is described. Nodal explants, initially established on MS medium, were transferred to WPM supplemented with combinations of BA and GA3. Maximum shoot multiplication was observed on explants cultured on medium supplemented with BA concentration higher than 1.1 μM, and 14 μM GA3. Although Stage II medium supplemented with BA concentration higher than 1.1 μM resulted in increased shoot multiplication, it also caused a decrease in shoot length. A negative carry over effect of GA3 on rooting was observed in subsequent Stage III cultures. The presence of GA3 in Stage II medium promoted shoot elongation, but it also caused a decrease in microcutting rooting. For this reason, 0.5 μM BA and 14 μM GA3 were selected for optimum Stage II shoot multiplication. Although 100% microcuttings formed roots when cultured on medium containing 6.0 μM NAA, significant callus formation was observed and ex vitro survival rate was low (49%). Rooting was achieved after 3 weeks with 82% of microcuttings on medium supplemented with 3 μM IBA. The survival rate of plantlets under ex vitro conditions was 100% after 3 weeks. Plants looked healthy with no visually detectable phenotypic variation based on observation of about 30 plants.

(80) Calculating Base Temperature and Leaf Appearance Rate for Sweet Viburnum

In crop models, it is important to determine the leaf area, because the amount of light interception by leaves influences two very important processes in the plant: photosynthesis and evaporation. Leaf area is dependent on leaf appearance and expansion rates. Leaf appearance rate is driven mainly by temperature. Although the influence of temperature on leaf area development is well known for several agronomic crops, there is no information for woody ornamentals. An experiment was conducted to study the relationship between temperature and leaf appearance of container-grown sweet viburnum. Plants were grown in field conditions in Gainesville, Fla., during two growing periods (Apr. to Aug. 2004 and Aug. 2004 to Jan. 2005). Daily maximum and minimum temperature and leaf appearance were recorded. Linear regression equations were fitted to data and maximum and minimum temperature and leaf appearance were recorded. Linear regression equations were fitted to data and base temperature was assumed to be 8 °C. Thermal time (°C d) was calculated as daily average maximum and minimum air temperature minus the base temperature and was regressed against leaf number. The sum of accumulated thermal time was found to be linearly correlated with leaf number. Phyllochron, which is the thermal time between the appearances of successive leaves, was estimated 51 °C per day. The information presented in this study will be useful in modeling water use of sweet viburnum in response to environmental conditions.

Plant Canopy Affects Sprinkler Irrigation Application Efficiency of Container-grown Ornamentals

Marketable size plants of sweet viburnum (Viburnum odoratissimum Ker-Gawl.), waxleaf ligustrum (Ligustrum japonicum Thunb.), and azalea (Rhododendron spp. L. `Southern Charm') grown in 11.4-L containers were irrigated with overhead impact sprinklers at container spacings ranging from 0 to 51 cm apart. Water reaching the substrate surface was quantified and the percentage of that applied calculated as percent capture (% capture). Percent capture is defined as the percentage of water falling above the plant within a projected vertical cylinder of a container that reaches the substrate surface. For all species, % capture increased linearly with the decline in adjacent canopy interaction, which results from canopies extending beyond the diameter of a container. Increases in total leaf area or leaf area outside the cylinder of a container, in conjunction with increasing distance between containers, were significantly (P < 0.05) correlated with increases in % capture for ligustrum and viburnum. Increases in % capture partially compensated for decreases in percentage of production area occupied by viburnum containers as distances between containers increased, but not for the other two species. Under commercial conditions, optimal irrigation efficiency would be achieved when plants are grown at the minimum spacing required for commercial quality. This spacing should not extend beyond the point where canopies become isolated.

Seasonal Irrigation Water Use Efficiency of Multi-Pot Box System

Abstract A Multi-Pot Box System (MPBS) was tested during three growing seasons (Fall 1996, Fall 1997, and Fall 1998) for efficient use of irrigation and rainfall in container-grown landscape plant production. This system was compared to a conventional (control) system consisting of black containers spaced on 30 cm (1 ft) centers. Results showed that the MPBS was successful in improving efficient use of irrigation and rainfall for Viburnum odoratissimum, Ker-Gawl. (sweet viburnum). Significant portions of the total rainfall were captured during the Fall 1996 (71.3%) and Fall 1997 (54%) seasons and later supplied to plants increasing rainfall effectiveness and irrigation water use efficiency. Thus, the need for the irrigation applications was significantly reduced for the plants grown in the MPBS. The seasonal irrigation water use efficiency (IWUE) was significantly higher for the MPBS compared to the control system in all seasons, demonstrating that significantly less irrigation water was necessary to produce the same amount or greater plant dry mass (shoot and root). Growth indices [(average width + height) / 2)] and shoot and root dry weights were usually significantly higher in all seasons (with exception of the shoot dry weight in Fall 1997) for the plants grown in the MPBS. Results indicate a potential opportunity for using the MPBS for efficient irrigation and water savings for container-grown landscape plants

観賞樹木の生育に及ぼす温周性と光周性の相互影響 (第4報)

Interrelated effects of daylength and winter chilling on the growth and dormancy of several woody plants were studied for two consecutive years.1. The shoot growth of Japanese holly (Ilex crenata Thunb.) cuttings remained linear throughout most of the test period at 16hr or more daylengths, though under daylengths less than 16hr the shoot of Japanese holly cuttings ceased to elongate after a certain period of growth. Shoot growth of Japanese black pine (Pinus thunbergii Parl. ) seedlings seemed daylength-independent.2. The shoot of Japanese holly cuttings did not respond to winter chilling, though they showed active growth under long day conditions. Contrary to Japanese holly cuttings, the shoot of trident maple (Acer buergerianum Miq.) seedlings became dormant even under long day conditions and eventually died unless it had previously been exposed to winter chilling. When trident maple seedlings were subjected to winter chilling, however, their shoots continued to grow vigorously even under short day conditions, that is, the shoot growth of trident maple seedlings was typically chilling-dependent. The shoot growth of Japanese privet (Ligustrum japonicum Thunb.) seedlings was facultative-long-day-dependent. The winter chilling treatment did not affect the shoot growth of sweet viburnum (Viburnum awabuki K. Koch) cuttings and Japanese black pine seedlings showed facultative-chilling-dependent responses along with facultative-long-day-dependent behavior, whereas that of sawleaf zelkova (Zelkova serrata (Thunb.) Makino) seedlings was facultative-chilling-dependent and daylength-independent.3. The seedlings of Japanese privet and Japanese black pine which were not exposed to winter chilling produced much fewer numbers of lateral shoots under both long and short day conditions than those exposed. No matter what daylengths Japanese privet seedlings and Japanese holly cuttings received, more than half of them bloomed when they were exposed previously to winter chilling, whereas those that were not subjected to winter chilling never bloomed.